Duolingo (DUOL) 10-Q 12 Nov 21 2021 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Nov. 11, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-40653
Entity Registrant Name	Duolingo, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-3055872
Entity Address, Address Line One	5900 Penn Avenue
Entity Address, City or Town	Pittsburgh
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	15206
City Area Code	(412)
Local Phone Number	567-6602
Title of 12(b) Security	Class A common stock, $0.0001 per share
Trading Symbol	DUOL
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Central Index Key	0001562088
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,796,838
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		21,675,473

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 549,440	$ 120,490
Accounts receivable	20,737	20,450
Deferred cost of revenues	19,726	13,585
Prepaid expenses and other current assets	6,441	3,855
Total current assets	596,344	158,380
Assets, Noncurrent
Property and equipment, net	8,010	6,428
Capitalized software, net	4,184	2,296
Operating lease right-of-use assets	8,231	8,073
Other assets	1,008	562
Total assets	617,777	175,739
Current liabilities
Accounts payable	8,708	2,196
Deferred revenues	80,460	54,792
Income tax payable	25	68
Accrued expenses and other current liabilities	9,452	8,634
Total current liabilities	98,645	65,690
Liabilities, Noncurrent
Long term obligation under operating leases	8,401	8,131
Total liabilities	107,046	73,821
Commitments and contingencies (Note 9)
Convertible preferred stock, $0.0001 par value, — shares issued and outstanding at September 30, 2021 and 19,074 shares issued and outstanding at December 31, 2020.	0	182,609
Stockholders’ equity (deficit)
Common stock, $0.0001 par value; 2,000,000 shares of Class A common stock authorized and 12,847 issued and outstanding at September 30, 2021; 30,000 shares of Class B common stock authorized and 24,598 issued and outstanding at September 30, 2021; 42,800 authorized shares of common stock; 12,794 issued and outstanding at December 31, 2020.	4	1
Additional paid-in capital	664,124	30,087
Accumulated deficit	(153,397)	(110,779)
Total stockholders’ equity (deficit)	510,731	(80,691)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 617,777	$ 175,739

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Convertible preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Convertible preferred stock, shares issued (in shares)	0	19,074,000
Convertible preferred stock, shares outstanding (in shares)	0	19,074,000
Common stock, shares authorized (in shares)		42,800,000
Common stock, shares issued (in shares)		12,794,000
Common stock, shares outstanding (in shares)		12,794,000
Common Class A
Common stock, par value (in usd per share)	$ 0.0001
Common stock, shares authorized (in shares)	2,000,000,000
Common stock, shares issued (in shares)	12,847,000
Common stock, shares outstanding (in shares)	12,847,000
Common Class B
Common stock, shares authorized (in shares)	30,000,000
Common stock, shares issued (in shares)	24,598,000
Common stock, shares outstanding (in shares)	24,598,000

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenues	$ 63,595	$ 45,305	$ 177,758	$ 113,428
Cost of revenues	18,078	13,101	49,234	33,124
Gross profit	45,517	32,204	128,524	80,304
Operating expenses:
Research and development	29,345	15,894	73,814	37,581
Sales and marketing	15,267	11,142	44,659	25,278
General and administrative	29,605	8,235	52,643	22,885
Total operating expenses	74,217	35,271	171,116	85,744
Loss from operations	(28,700)	(3,067)	(42,592)	(5,440)
Other (expense) income, net	(219)	(86)	43	116
Loss before provision for income taxes	(28,919)	(3,153)	(42,549)	(5,324)
Provision for income taxes	51	23	69	45
Net comprehensive (loss) income	(28,970)	(3,176)	(42,618)	(5,369)
Net (loss) income	$ (28,970)	$ (3,176)	$ (42,618)	$ (5,369)
Net loss per share attributable to Class A and Class B common stockholders, basic (in usd per share)	$ (0.98)	$ (0.25)	$ (2.29)	$ (0.43)
Net loss per share attributable to Class A and Class B common stockholders, diluted (in usd per share)	$ (0.98)	$ (0.25)	$ (2.29)	$ (0.43)

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit
Convertible preferred stock beginning balance (in shares) at Dec. 31, 2019	18,247,000
Convertible preferred stock beginning balance at Dec. 31, 2019	$ 137,686
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series G convertible preferred stock, net $24 of fees (in shares)	241,000
Issuance of Series G convertible preferred stock, net $24 of fees	$ 9,976
Convertible preferred stock ending balance (in shares) at Sep. 30, 2020	18,488,000
Convertible preferred stock ending balance at Sep. 30, 2020	$ 147,662
Beginning balance (in shares) at Dec. 31, 2019		12,406,000
Beginning balance at Dec. 31, 2019	(83,976)	$ 1	$ 11,026	$ (95,003)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Stock-based compensation	4,517		4,517
Stock options exercised (in shares)		192,000
Stock options exercised	1,130		1,130
Net loss attributable to Class A and Class B common shareholders	(5,369)			(5,369)
Ending balance (in shares) at Sep. 30, 2020		12,598,000
Ending balance at Sep. 30, 2020	$ (83,698)	$ 1	16,673	(100,372)
Convertible preferred stock beginning balance (in shares) at Jun. 30, 2020	18,488,000
Convertible preferred stock beginning balance at Jun. 30, 2020	$ 147,662
Convertible preferred stock ending balance (in shares) at Sep. 30, 2020	18,488,000
Convertible preferred stock ending balance at Sep. 30, 2020	$ 147,662
Beginning balance (in shares) at Jun. 30, 2020		12,482,000
Beginning balance at Jun. 30, 2020	(82,884)	$ 1	14,311	(97,196)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Stock-based compensation	1,682		1,682
Stock options exercised (in shares)		116,000
Stock options exercised	680		680
Net loss attributable to Class A and Class B common shareholders	(3,176)			(3,176)
Ending balance (in shares) at Sep. 30, 2020		12,598,000
Ending balance at Sep. 30, 2020	$ (83,698)	$ 1	16,673	(100,372)
Convertible preferred stock beginning balance (in shares) at Dec. 31, 2020	19,074,000
Convertible preferred stock beginning balance at Dec. 31, 2020	$ 182,609
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)	(19,074,000)
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	$ (182,609)
Convertible preferred stock ending balance (in shares) at Sep. 30, 2021	0
Convertible preferred stock ending balance at Sep. 30, 2021	$ 0
Beginning balance (in shares) at Dec. 31, 2020		12,794,000
Beginning balance at Dec. 31, 2020	(80,691)	$ 1	30,087	(110,779)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Stock-based compensation	$ 26,120		26,120
Stock options exercised (in shares)	1,134,000	1,134,000
Stock options exercised	$ 7,322		7,322
Issuance of common stock in connection with initial public offering, net of underwriting discounts and issuance costs (in shares)		4,466,000
Issuance of common stock in connection with initial public offering, net of underwriting discounts and issuance costs	426,192	$ 1	426,191
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)		19,074,000
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	182,609	$ 2	182,607
Common stock repurchased and retired (in shares)		(23,000)
Common stock repurchased and retired	(868)		(868)
Options repurchased	(7,335)		(7,335)
Net loss attributable to Class A and Class B common shareholders	(42,618)			(42,618)
Ending balance (in shares) at Sep. 30, 2021		37,445,000
Ending balance at Sep. 30, 2021	$ 510,731	$ 4	664,124	(153,397)
Convertible preferred stock beginning balance (in shares) at Jun. 30, 2021	19,074,000
Convertible preferred stock beginning balance at Jun. 30, 2021	$ 182,609
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)	(19,074,000)
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	$ (182,609)
Convertible preferred stock ending balance (in shares) at Sep. 30, 2021	0
Convertible preferred stock ending balance at Sep. 30, 2021	$ 0
Beginning balance (in shares) at Jun. 30, 2021		13,271,000
Beginning balance at Jun. 30, 2021	(93,777)	$ 1	30,649	(124,427)
Increase (Decrease) in Stockholders' Deficit [Roll Forward]
Stock-based compensation	20,662		20,662
Stock options exercised (in shares)		634,000
Stock options exercised	4,015		4,015
Issuance of common stock in connection with initial public offering, net of underwriting discounts and issuance costs (in shares)		4,466,000
Issuance of common stock in connection with initial public offering, net of underwriting discounts and issuance costs	426,192	$ 1	426,191
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)		19,074,000
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	182,609	$ 2	182,607
Net loss attributable to Class A and Class B common shareholders	(28,970)			(28,970)
Ending balance (in shares) at Sep. 30, 2021		37,445,000
Ending balance at Sep. 30, 2021	$ 510,731	$ 4	$ 664,124	$ (153,397)

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Statement of Stockholders' Equity [Abstract]
Issuance costs	$ 24	$ 24

UNAUDITED CONDENSED CONSOLIDA_6

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (42,618)	$ (5,369)
Adjustments to reconcile net loss to net cash used for operating activities:
Depreciation and amortization	1,969	1,649
Stock-based compensation	26,120	4,517
Changes in assets and liabilities
Deferred revenue	25,668	19,689
Accounts receivable	(287)	(7,907)
Deferred cost of revenues	(6,141)	(4,830)
Prepaid expenses and other current assets	(2,559)	451
Accounts payable	6,512	837
Accrued expenses and other current liabilities	409	4,138
Noncurrent assets and liabilities	(335)	852
Net cash provided by operating activities	8,738	14,027
Cash flows from investing activities:
Capitalized software	(2,035)	(123)
Purchase of property and equipment	(3,063)	(2,557)
Net cash used for investing activities	(5,098)	(2,680)
Cash flows from financing activities:
Issuance of common stock in connection with the initial public offering, net of underwriting discounts and issuance costs	426,191	0
Net proceeds from issuance of convertible preferred stock	0	9,976
Proceeds from exercise of stock options	7,322	1,130
Repurchases of stock options	(7,335)	0
Repurchase of common stock	(868)	0
Net cash provided by financing activities	425,310	11,106
Net increase in cash and cash equivalents	428,950	22,453
Cash and cash equivalents - Beginning of period	120,490	59,843
Cash and cash equivalents - End of period	549,440	82,296
Supplemental disclosure of cash flow information:
Cash paid for interest	0	0
Cash paid for income taxes	94	11
Supplemental disclosure of noncash operating activities:
Implementation costs for cloud computing included in accrued expenses	27	0
Supplemental disclosure of noncash investing activities:
Capitalized software included in accrued expenses	337	0
Property and equipment included in accrued expenses	$ 2	$ 55

DESCRIPTION OF THE BUSINESS AND

DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION Duolingo, Inc. (the “Company” or “Duolingo”) was formed on August 18, 2011 and the Duolingo app was launched to the general public on June 19, 2012. The Company’s headquarters are located in Pittsburgh, Pennsylvania. On July 30, 2021, Duolingo completed its Initial Public Offering (“IPO”) of 5,872 shares of its Class A common stock at a price to the public of $102.00 per share, 4,466 of which were sold by the Company and 1,406 of which were sold by certain selling stockholders, which includes the exercise in full by the underwriters of their option to purchase from the Company an additional 766 shares of the Company’s Class A common stock. The gross proceeds to the Company from the IPO were $455,532, before deducting underwriting discounts and commissions and offering expenses payable by the Company. The Company did not receive any proceeds from the sale of shares of Class A common stock in the offering by the selling stockholders. Immediately prior to the completion of the IPO, all convertible preferred stock outstanding, totaling approximately 19,074 shares, was automatically converted into an equivalent number of shares of Class B common stock on a one-to-one basis and their carrying value of $182,609 was reclassified to stockholders’ equity (deficit). Additionally, on July 15, 2021, 6,930 shares held by our founders were exchanged from Class A common stock into Class B common stock. Duolingo is a US-based language-learning website and mobile app, as well as a digital language proficiency assessment exam. The Company has a freemium business model: the app and the website are accessible free of charge, although Duolingo also offers a premium service, Duolingo Plus, for a subscription fee. As of the date of this filing, Duolingo offers courses in 40 different languages, including Spanish, English, French, German, Italian, Portuguese, Japanese and Chinese. We have locations in the United States and China. Principles of Consolidation —The unaudited condensed consolidated financial statements include the accounts of the Company and subsidiaries over which the Company has control. All intercompany transactions and balances have been eliminated. Basis of Presentation —The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) from the Company’s accounting records and reflect the consolidated financial position and results of operations for the three and nine months ended September 30, 2021 and 2020. Unless otherwise specified, all dollar amounts are referred to in thousands. The unaudited condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such SEC rules. We believe that the disclosures made are adequate to make the information presented not misleading. In our opinion, all adjustments considered necessary for a fair presentation of the financial statements have been included, and all adjustments are of a normal and recurring nature. We consistently applied the accounting policies consistent with the annual consolidated financial statements elsewhere in this this Quarterly Report on Form 10-Q, in preparing these unaudited condensed consolidated financial statements, with the exception of accounting standard updates described in Note 2, “Recently Adopted Accounting Pronouncements.” These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes for the fiscal year ended December 31, 2020 included in the final prospectus

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Under the JOBS Act, emerging growth companies also can delay adopting new or revised accounting standards until such time as those standards would otherwise apply to private companies. While we have not historically delayed the adoption of new or revised accounting standards until such time as those standards would apply to private companies, we have elected to take advantage of this extended transition period and, as a result, our operating results and financial statements in the future may not be comparable to the operating results and financial statements of companies who have adopted the new or revised accounting standards. Accounting Principles —The financial statements and accompanying notes are prepared in accordance with generally accepted accounting principles in the United States of America (GAAP). Use of Estimates— The preparation of unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant estimates and assumptions reflected in the consolidated financial statements include, but are not limited to, useful lives of property and equipment, valuation of deferred tax assets and liabilities, stock-based compensation, common stock valuation, operating lease right-of-use assets and liabilities, capitalization of internally developed software and associated useful lives and contingent liabilities. Actual results may differ materially from such estimates. Management believes that the estimates, and judgments upon which they rely, are reasonable based upon information available to them at the time that these estimates and judgments are made. To the extent that there are material differences between these estimates and actual results, the Company’s consolidated financial statements will be affected. Deferred Offering Costs— Deferred offering costs, which consist of direct incremental legal, accounting, and consulting fees relating to the IPO, are capitalized. Deferred offering costs of $4,865 were offset against IPO proceeds upon the consummation of the IPO, of which $1,123 are expected to be paid in the fourth quarter of 2021. This amount was included in the unaudited condensed consolidated balance sheets within Accrued expenses and other current liabilities at September 30, 2021. Cash and Cash Equivalents— Cash consists primarily of cash on hand and bank deposits. Cash equivalents consist primarily of money market accounts with maturities of three months or less at the date of acquisition and are stated at cost, which approximates fair value. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times. The following table shows the breakout between cash and money market funds. September 30, December 31, Cash $ 39,694 $ 20,428 Money market funds 509,746 100,062 Total $ 549,440 $ 120,490 The Money market funds are considered Level 1 financial assets. Level 1 financial assets use inputs that are the unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Advertising Costs— Advertising costs were approximately $12,013 and $31,764 for the three and nine months ended September 30, 2021 and $8,843 and $19,338 for the three and nine months ended September 30, 2020, respectively, and are included within Sales and marketing in the unaudited condensed consolidated statement of operations and comprehensive loss. Income Taxes— The Company’s provision for income taxes is computed by using an estimate of the annual effective tax rate, adjusted for discrete items taken into account in the relevant period, if any. Each quarter, the annual effective income tax rate is recomputed and if there are material changes in the estimate, a cumulative adjustment is made. Contributors— On March 10, 2021, the Company announced that it was ending its non-employee volunteer program, which began in 2013 to build and improve language courses. As part of this change, those contributors who participated in the program became eligible to receive a one-time award, up to an aggregate amount of approximately $5,098, including fees paid to process payments of approximately $526. The Company accounted for this under Financial Accounting Standards Board (“FASB”) Accounting Standards Codifications (“ASC”) 958-720, Not-For-Profit Entities - Other Expenses and ASC 720-25, Contributions Made , based on the nature of this contribution, which is an unconditional promise. The Company recorded the initial charge during the three months ended March 31, 2021, which is when the Company made the unconditional promise to pay. During the three months ended June 30, 2021 the amount previously reserved was reduced by $878 to reflect those awards that were not claimed, resulting in a reduction of the expense, bringing the total amount to $4,220. This amount is included within Sales and marketing in the unaudited condensed consolidated statement of operations and comprehensive loss. Concentration of Credit Risk —The Company’s concentration of credit risk relates to financial institutions holding the Company’s cash and cash equivalents and platforms with significant accounts receivable balances and revenue transactions. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times. Management believes that the financial institutions that hold the Company’s deposits are financially credit worthy and, accordingly, minimal credit risk exists with respect to those balances. The majority of our revenue comes through our subscriptions and advertising streams and payments are made to Duolingo through service providers. The top three, Apple, Google, and Stripe, accounted for 49.8%, 29.0%, and 14.4% of total accounts receivable as of September 30, 2021, respectively. The top three service providers, Apple, Google and Stripe, accounted for 47.8%, 28.9% and 13.8% of total accounts receivable as of December 31, 2020, respectively. Three service providers, Apple, Google, and Stripe, processed 51.6%, 29.3% and 12.1% and 51.2%, 29.0%, and 11.0% of total revenue for the three and nine months ended September 30, 2021, respectively. Three service providers, Apple, Google, and Stripe, processed 50.7%, 25.6%, and 11.0% of total revenue for the three months ended September 30, 2020, respectively. Two services providers, Apple and Google, processed 51.5% and 26.8% for the nine months ended September 30, 2020. Stock-Based Compensation —The Company accounts for equity-based compensation using the fair value method as set forth in the ASC 718, Compensation—Stock Compensation , which requires the measurement and recognition of compensation expense for all stock-based payment awards based on estimated fair values. This method requires companies to estimate the fair value of stock-based compensation on the date of grant using an option pricing model. The Company estimates the fair value of each equity-based payment award on the date of grant using the Black-Scholes pricing model. The Black-Scholes model determines the fair value of equity-based payment awards based on the fair value of the underlying common stock on the date of grant and requires the use of estimates and assumptions, including the fair value of the Company’s common stock, exercise price of the stock option, expected volatility, expected life, risk-free interest rate and dividend rate. The Company estimates the expected volatility of its stock options by taking the average historical volatility of a group of comparable publicly traded companies over a period equal to the expected life of the options; it is not practical for the Company to estimate its own volatility due to the lack of historical prices. The expected term of the options is determined in accordance with existing equity agreements as the underlying options are assumed to be exercised upon the passage of time. The risk-free interest rate is the estimated average interest rate based on US Treasury zero-coupon notes with terms consistent with the expected life of the awards. The expected dividend yield is zero as the Company does not anticipate paying any recurring cash dividends in the foreseeable future. The Company accounts for forfeitures as they occur. Restricted Stock Units (RSUs) The Company began to grant RSUs in November 2020. The fair value of RSUs is estimated based on the fair value of the Company’s common stock on the date of grant. Each RSU award granted prior to the IPO vests based upon the satisfaction, during the term of the RSUs, of two requirements: length of service and a liquidity event defined as a change in control or a qualified IPO. The service-based vesting condition for the majority of these awards is satisfied over four years. The liquidity-based vesting condition is satisfied upon the occurrence of a qualifying liquidity event. The Company measures and recognizes compensation expense for all stock-based awards based on the estimated fair value of the award. Prior to July 30, 2021, no stock-based compensation expense had been recognized for RSUs because the liquidity-based vesting condition had not been probable of being satisfied. Upon the IPO, the liquidity-based vesting condition was satisfied and $2,035 of stock-based compensation expense was recognized related to these awards during the three months ended September 30, 2021. Of that amount, $1,332, $210 and $493 was included within Research and development, Sales and marketing and General and administrative, respectively, in the unaudited condensed consolidated statement of operations and comprehensive loss. Performance-based RSUs In June 2021, the Company granted 1,800 (one million eight-hundred thousand) performance-based RSUs to the Company’s founders (“Founder Awards”). The Founder Awards are divided into ten equal tranches with each tranche becoming eligible to vest upon achievement of the specified stock-price hurdles. The Founder Awards vest upon the satisfaction of both a service-based condition and a performance-based condition and generally are settled one year after vesting. The service-based condition is satisfied as to 25% of the Founder Awards on each anniversary of the completion of the IPO, subject to the continuous service of the founders through the applicable date. The fair value of the Founder Awards is determined using a Monte Carlo simulation model. The associated stock-based compensation is recorded over the derived service period, using the accelerated attribution method. If the stock-price hurdles are met sooner than the requisite service period, the stock-based compensation expense will be adjusted to prospectively recognize the remaining expense over the remaining derived service period. Provided that the founders continue to provide services to us, stock-based compensation expense is recognized over the derived service period, regardless of whether the stock-price hurdles are achieved. The first tranche was met during the three months ended September 30, 2021. The Company recognized $8,267 of stock-based compensation expense related to these awards, which is included within General and administrative in the unaudited condensed consolidated statement of operations and comprehensive loss. Recently Adopted Accounting Pronouncements In August 2018, the FASB issued Accounting Standard Update (“ASU”) No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract (ASU 2018-15) . ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The Company adopted this guidance on January 1, 2021 and it did not have a material impact on its unaudited condensed consolidated financial statements and related disclosures upon adoption. Recently Issued Pronouncements Not Yet Adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

REVENUE

REVENUE	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE The Company has three predominant sources of revenue; time-based subscriptions, in-app advertising placement by third parties, and the Duolingo English Test. Revenue is recognized upon transfer of control of promised products or services to users in an amount that reflects the consideration the Company expects to receive in exchange for those services. The Company does not enter into contracts with a customer that contain multiple promises that result in multiple performance obligations. Revenue is recorded net of taxes assessed by a government authority that are both imposed on and concurrent with specific revenue transactions between us and our users. Revenue from time-based subscriptions includes a stand-ready obligation to provide hosting services that are consumed by the customer over the subscription period. Users can purchase Duolingo monthly or they can purchase a six-month or year-long subscription and pay for the subscription at the time of purchase. Under the year-long subscription, users can also purchase a single plan or a family plan, which allows up to six users to be on one subscription. Therefore, such payments are initially recorded to deferred revenue. The user has the ability to download limited content offline. However, as there is a significant level of integration and interdependency with the online functionality, the Company considers the service to be a single performance obligation for the online and offline content. The Company enters into arrangements with advertising networks to monetize the in-app advertising inventory. Revenue from in-app advertising placement is recognized at a point in time when the advertisement is placed and is based upon the amount received. Duolingo English Test revenue is generally recognized once the tests have gone through the proctoring process and a certification decision has been made. This process usually takes less than 48 hours after the test has been completed and uploaded. Customers have 90 days from the date of purchase to take the exam or their purchase will expire and revenue will be recognized. Virtually all customers complete their exams prior to expiration. Sometimes organizations may purchase tests in bulk via coupons with a one year expiration date. The Company will defer revenue from all tests that haven’t been proctored nor expired. The Company’s users have the option to purchase consumable in-app virtual goods. The Company recognizes revenue over the period in which the user consumes the virtual good, which is generally within a month. Principal Agent Considerations —The Company makes its application available to be downloaded through third-party digital distribution service providers. Users who purchase subscriptions also pay through the respective app stores. The Company evaluates the purchases via third-party payment processors to determine whether its revenues should be reported gross or net of fees retained by the payment processor. The Company is the principal in the transaction with the end user as a result of controlling, hosting, and integrating the delivery of the virtual items to the end user. The Company records revenue gross as a principal and records fees paid to third-party payment processors as Cost of revenues. Contract Balances —Deferred revenue mostly consists of payments we receive in advance of revenue recognition, and is mostly related to time-based subscriptions, which will be recognized into revenue over the course of the upcoming year (recognized over 12 months or less). Additionally, the Duolingo English Test has deferred revenue related to tests that have been purchased, but will not be recognized until the tests have been proctored. Disaggregation of Revenue In accordance with ASC 606, Revenue from Contracts with Customers , the Company disaggregates revenue from contracts with customers into source of revenue, which most closely depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. Information regarding source of revenues: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Over time $ 46,030 $ 32,317 $ 129,587 $ 82,762 Point in time 17,565 12,988 48,171 30,666 Total revenue $ 63,595 $ 45,305 $ 177,758 $ 113,428 Information regarding revenue by stream: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Revenues: Subscription $ 46,030 $ 32,317 $ 129,587 $ 82,762 Advertising 9,029 6,720 27,360 18,536 Duolingo English Test 6,695 5,607 16,563 10,958 Other (1) 1,841 661 4,248 1,172 Total revenues $ 63,595 $ 45,305 $ 177,758 $ 113,428 ________________ (1) Other revenue is mainly comprised of in-app purchases of virtual goods. Changes in deferred revenues were as follows: Nine Months Ended September 30, 2021 2020 Beginning balance—January 1 $ 54,792 $ 26,307 Amount from beginning balance recognized into revenue (51,254) (24,848) Recognition of deferred revenue (83,088) (59,495) Deferral of revenue 160,010 104,032 Ending balance—September 30 $ 80,460 $ 45,996

PROPERTY and EQUIPMENT, net

PROPERTY and EQUIPMENT, net	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
PROPERTY and EQUIPMENT, net	PROPERTY and EQUIPMENT, net Property and equipment consists of the following as of September 30, 2021 and December 31, 2020: September 30, December 31, Leasehold improvements $ 9,862 $ 7,536 Furniture, fixtures and equipment 2,699 1,959 Total property and equipment 12,561 9,495 Less: accumulated depreciation (4,551) (3,067) Total property and equipment, net $ 8,010 $ 6,428 Depreciation expense was $545 and $1,485 for the three and nine months ended September 30, 2021 and $453 and $1,173 for the three and nine months ended September 30, 2020, respectively, and is predominately included within General and administrative, with nominal amounts in Cost of revenues, Research and development and Sales and marketing in the Company’s consolidated statement of operations and comprehensive loss.

CAPITALIZED SOFTWARE, net

CAPITALIZED SOFTWARE, net	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
CAPITALIZED SOFTWARE, net	CAPITALIZED SOFTWARE, net Capitalized software consists of the following as of September 30, 2021 and December 31, 2020: September 30, December 31, Capitalized software $ 10,553 $ 8,181 Less: accumulated amortization (6,369) (5,885) Capitalized software, net $ 4,184 $ 2,296 Amortization expense of $188 and $484 for the three and nine months ended September 30, 2021, and $174 and $476 for the three and nine months ended September 30, 2020 is recorded in the Company’s consolidated statement of operations and comprehensive loss, respectively. Amortization expense is included within the following financial statement line items within the Company’s consolidated statement of operations and comprehensive loss: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Cost of revenues $ — $ 26 $ — $ 77 Sales and marketing 188 148 484 399 Total $ 188 $ 174 $ 484 $ 476 The Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the estimated undiscounted future cash flows expected to result from the use and eventual disposition of an asset is less than the carrying amount of the asset, an impairment loss is recognized. Measurement of an impairment loss is based on the fair value of the asset. No assets were impaired during the three and nine months ended September 30, 2021 and 2020.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The income tax provision for interim periods is comprised of tax on ordinary income (loss) provided at the most recent projected annual effective tax rate (“PAETR”), adjusted for the tax effect of discrete items. Management estimates the PAETR each quarter based on the forecasted annual pretax income or (loss). The Company is required to reduce deferred tax assets by a valuation allowance if, based on all available evidence, it is considered more likely than not that some portion or all of the benefit of the deferred tax assets will not be realized in future periods. The Company also records the income tax impact of certain discrete, unusual or infrequently occurring items including changes in judgment about valuation allowances and effects of changes in tax laws or rates, in the interim period in which they occur. The actual year-to-date income tax expense is the product of the most current PAETR and the actual year-to-date pretax income (loss) adjusted for any discrete tax items. Items unrelated to current period ordinary income or (loss) are recognized entirely in the period identified as a discrete item of tax. The income tax expense for a particular quarter, except for the first quarter, is the difference between the year-to-date calculation of income tax expense and the year-to-date calculation for the prior quarter. Items unrelated to current period ordinary income or (loss) are recognized entirely in the period identified as a discrete item of tax. The inclusion of discrete items in a particular quarter can cause the actual effective rate for that quarter to vary significantly from the PAETR. Therefore, the actual effective income tax rate for a particular quarter can vary significantly based upon the jurisdictional mix and timing of actual earnings compared to projected annual earnings, permanent items, earnings for those jurisdictions that maintain a valuation allowance, tax associated with jurisdictions excluded from the PAETR calculation and discrete items. Annual Effective Tax Rate The PAETR was (0.2)% and (0.7)% as of the three months ended September 30, 2021 and 2020, respectively. The PAETR for the nine months ended September 30, 2021 and 2020, was (0.2)% and (0.8)%, respectively. The tax expense for the current year quarter includes the impact of a discrete tax expense related to state income tax expense obligations for the 2017-2019 tax years. The PAETR was lower than the US federal statutory rate of 21.0% primarily due to the impact of maintaining a US valuation allowance provided on US deferred tax assets. The Company continues to maintain a full valuation allowance on US federal and state net deferred tax assets for the period ending September 30, 2021 as a result of pre-tax losses incurred since the Company’s inception in early 2012. The Company is projecting pre-tax loss in 2021. Current and Prior Period Tax Expense For the three and nine months ended September 30, 2021, the Company recognized income tax expense of $51 and $69 on pretax loss of $28,919 and $42,549, respectively.

CONVERTIBLE PREFERRED STOCK

CONVERTIBLE PREFERRED STOCK	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
CONVERTIBLE PREFERRED STOCK	CONVERTIBLE PREFERRED STOCKImmediately prior to the completion of the IPO on July 30, 2021, all convertible preferred stock outstanding, totaling approximately 19,074 shares, was automatically converted into an equivalent number of shares of Class B common stock on a one-to-one basis and their carrying value of $182,609 was reclassified to stockholders’ equity (deficit). The following table summarizes the convertible preferred stock outstanding immediately prior to the conversion into common stock and as of December 31, 2020: Shares Series Authorized Outstanding Per share price Aggregate liquidation preference Funds received Fees incurred Carrying value of convertible preferred stock A 3,865 3,865 $ 0.85 $ 3,300 $ 3,300 $ 52 $ 3,248 B 6,298 6,298 2.38 15,000 15,000 60 14,940 C 2,948 2,948 6.78 20,000 20,000 112 19,888 D 3,154 3,154 14.27 45,000 45,000 146 44,853 E 1,224 1,224 20.43 25,000 25,000 92 24,909 F 758 758 39.57 30,000 30,000 153 29,848 G 241 241 41.38 10,000 10,000 24 9,976 H 586 586 59.77 35,000 35,000 52 34,947 Total 19,074 19,074 $ 183,300 $ 183,300 $ 691 $ 182,609

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION Prior to the IPO, the Company granted options to purchase shares of the Company’s common stock and restricted stock units in respect of shares of the Company’s common stock to employees, directors and consultants to purchase shares of the Company’s common stock under the Company’s 2011 Equity Incentive Plan. In July 2021, Duolingo adopted the 2021 Incentive Award Plan (2021 Plan) and the 2021 Employee Stock Purchase Plan (ESPP), each of which became effective on July 26, 2021 in connection with the IPO. An aggregate of 7,946 shares and 1,119 shares of Class A common stock were made available for future issuance under the 2021 Plan and ESPP, respectively. The 2021 Plan permits the granting of incentive stock options and nonqualified stock options. The Company’s stock options vest based on terms in the stock option agreements and generally vest over four years and have a term of ten years subject to the continuous service to the Company by the optionee. Incentive stock options may be granted at an exercise price of not less than 100% of the estimated fair value of the underlying Class A common stock at the date of the grant. Stock option activity as of September 30, 2021 is set forth below: Number of Weighted- Weighted- average remaining contractual life (years) Aggregate intrinsic value Options outstanding at January 1, 2021 8,365 $ 10.68 7.47 $ 230,596 Granted 72 52.80 Exercised (1,134) 6.45 Repurchased (220) 4.81 Forfeited and expired (59) 13.43 Options outstanding at September 30, 2021 7,024 $ 11.94 7.01 $ 1,084,464 Options exercisable at September 30, 2021 4,830 $ 9.79 6.42 $ 756,259 The total intrinsic value of options exercised was approximately $102,628 for the period ending September 30, 2021. RSU activity for the nine months ended September 30, 2021 is set forth below: Restricted stock units Weighted- Outstanding at January 1, 2021 34 $ 38.08 Granted 671 66.43 Vested — — Forfeited (5) 106.59 Outstanding at September 30, 2021 700 $ 64.77 Prior to July 30, 2021, no stock-based compensation expense had been recognized for RSUs because the liquidity-based vesting condition had not been probable of being satisfied. Upon the IPO, the liquidity-based vesting condition was met and $2,035 of stock-based compensation expense was recognized related to these awards. As of September 30, 2021, there was approximately $15,857 of unrecognized compensation cost related to stock options granted under the plan. That cost is expected to be recognized over a weighted-average period of approximately two years. The amount of unrecognized compensation expense for RSUs as of September 30, 2021 was $40,392 with a weighted average remaining contractual life of four years, for a total unrecognized compensation expense of $56,249. There were 7,842 shares available for grant at September 30, 2021. Performance-based RSUs In June 2021, the Company granted an aggregate of 1,800 performance-based RSUs (the “Founder Awards”) to the Company’s founders. The Founder Awards vest upon the satisfaction of both a service-based condition and a performance-based condition and generally are settled 1 year after vesting. The service-based condition is satisfied as to 25% of the Founder Awards on each anniversary of the completion of the IPO, subject to the continuous service of the founders through the applicable date. The performance-based condition will be satisfied with respect to each of 10 equal tranches only if the trailing 60-calendar day volume-weighted average closing trading price of the Company’s Class A common stock reaches certain stock-price hurdles for each such tranche, as set forth below, over a period of 10 years from the date of grant. If stock-price hurdles fail to be reached prior to the tenth anniversary of the date of grant, no portion of the Founder Awards will vest. Further, any RSUs associated with stock-prices hurdle not achieved by the tenth anniversary of the date of grant will terminate and be cancelled for no additional consideration to the founders. The stock-price hurdles and number of RSUs eligible to vest will be adjusted to reflect any stock splits, stock dividends, combinations, reorganizations, reclassifications, or similar events under the 2021 Plan. The Founder Awards will be settled in shares of the Company’s Class B common stock. Tranche Company Stock Price Hurdle Number of RSUs Eligible to Vest 1 $ 127.50 90 2 $ 153.00 90 3 $ 178.50 90 4 $ 204.00 180 5 $ 255.00 180 6 $ 306.00 180 7 $ 357.00 180 8 $ 408.00 180 9 $ 612.00 270 10 $ 816.00 360 The Company estimated the grant date fair value of the Founder Awards using a model based on multiple stock-price paths developed through the use of a Monte Carlo simulation that incorporates into the valuation the possibility that the stock-price hurdles may not be satisfied. The weighted-average grant date fair value of the Founder Awards was estimated to be $61.56 per share, and the Company estimates that it will recognize total stock-based compensation expense of approximately $110,817 over the derived service period of each of the ten separate tranches which is between 3.58 – 5.92 years. If the stock-price hurdles are met sooner than the requisite service period, the stock-based compensation expense will be adjusted to prospectively recognize the remaining expense over the remaining derived service period. Provided that the founders continue to provide services to the Company, stock-based compensation expense is recognized over the derived service period, regardless of whether the stock-price hurdles are achieved. The first tranche was met during the three months ended September 30, 2021. The Company recognized $8,267 of stock-based compensation expense related to these awards, which is included within General and administrative in the unaudited condensed consolidated statement of operations and comprehensive loss. In February 2021, the Company initiated a tender offer which allowed employees to sell up to 10% of their vested options or shares back to the Company at selling price of $59.77, which was above fair market value of $38.08. The Company paid $13,479 and incurred $5,275 of additional compensation expense related to this tender representing the difference between the aggregate selling price and fair market value of the options and shares sold, and a $7,335 increase to Additional paid-in capital. As a result of this tender, 220 options were put back into the option pool and 23 shares were retired with an $868 increase to Additional paid-in capital. Upon the IPO, vesting of stock option grants to executive officers were accelerated, which resulted in an additional $5,574 of compensation expense during the three months ended September 30, 2021. This is included within General and administrative in the unaudited condensed consolidated statement of operations and comprehensive loss. Total stock-based compensation expense was $20,662 and $26,120 for the three and nine months ended September 30, 2021, respectively and $1,682 and $4,517 or the three and nine months ended September 30, 2020, respectively. Stock based compensation expense is included in the consolidated statements of operations as shown in the following table: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Cost of revenues $ 6 $ 3 $ 8 $ 4 Research and development 3,533 526 5,749 1,505 Sales and marketing 408 116 548 296 General and administrative 16,715 1,037 19,815 2,712 Total $ 20,662 $ 1,682 $ 26,120 $ 4,517

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Legal Proceedings — From time to time, the Company may become involved in various legal proceedings in the ordinary course of its business and may be subject to third-party infringement claims. Sales and use and value-added tax (VAT) — The Company determined that it was required to pay sales and use and VAT taxes in various jurisdictions. The Company is in the process of filing voluntary disclosure agreements with certain jurisdictions and remitting the estimated taxes. If these jurisdictions determine that additional amounts are necessary, the Company will be required to pay accordingly. Related Parties — The Company has determined that there were no transactions with related parties as of or during the three and nine months ended September 30, 2021 and 2020.

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	9 Months Ended
	Sep. 30, 2021
Other Liabilities Disclosure [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following: September 30, December 31, Sales and VAT tax accrual $ 2,289 $ 2,301 Obligations under current leases 1,542 1,111 Employee related benefits 1,143 889 Marketing related accruals 1,086 1,513 Other 3,392 2,820 Total $ 9,452 $ 8,634

EMPLOYEE BENEFIT PLAN

EMPLOYEE BENEFIT PLAN	9 Months Ended
	Sep. 30, 2021
Postemployment Benefits [Abstract]
Defined Contribution Plan	EMPLOYEE BENEFIT PLANThe Company sponsors a profit sharing plan with a 401(k) feature, the Duolingo Retirement Plan, (the “Plan”) for eligible employees. The current Plan, effective January 1, 2021, provides for Company safe harbor matching contributions of 100% of the first 4% of the employees’ elective deferrals and 50% of the next 2%, with vesting starting upon the first day of employment. The prior year Plan provided for Company safe harbor matching contributions of 100% of the first 3% of the employees’ elective deferrals and 50% of the next 2%, with vesting starting upon the first day of employment. The Company also has the option to make discretionary matching or profit sharing contributions. The Company made safe harbor matching contributions of approximately $877 and $2,360 for the three and nine months ended September 30, 2021, respectively and $495 and $1,308 for the three and nine months ended September 30, 2020, respectively. The Company did not make any discretionary matching or profit sharing contributions during the nine months ended September 30, 2021 or 2020.

EARNINGS PER SHARE

EARNINGS PER SHARE	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Basic and diluted net loss per share attributable to common stockholders is presented in conformity with the two-class method required for participating securities. Prior to the automatic conversion of all of its convertible preferred stock outstanding into Class B common stock upon the IPO, the Company considered all series of its convertible preferred stock to be participating securities. Under the two-class method, the net loss attributable to common stockholders is not allocated to the convertible preferred stock as the holders of the convertible preferred stock do not have a contractual obligation to share in the Company’s losses. Basic net loss per share attributable to common stockholders is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase. The diluted net loss per share attributable to common stockholders is calculated by giving effect to all potential dilutive common stock equivalents outstanding for the period. Three Months Ended September 30, Nine Months Ended September 30, (In thousands, except per share data) 2021 2020 2021 2020 Numerator: Net loss attributable to Class A and Class B common shareholders $ (28,970) $ (3,176) $ (42,618) $ (5,369) Denominator: Weighted-average shares in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted 29,531 12,530 18,600 12,471 Basic loss per common share $ (0.98) $ (0.25) $ (2.29) $ (0.43) Diluted loss per common share $ (0.98) $ (0.25) $ (2.29) $ (0.43) The rights, including the liquidation and dividend rights, of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to 20 votes per share. Each share of Class B common stock is convertible into a share of Class A common stock voluntarily at any time by the holder, and automatically upon certain events. The Class A common stock has no conversion rights. As the liquidation and dividend rights are identical for Class A and Class B common stock, the undistributed earnings are allocated on a proportional basis and the resulting net loss per share attributable to common stockholders will, therefore, be the same for both Class A and Class B common stock on an individual or combined basis. Since the Company was in a net loss position for the three and nine months ended September 30, 2021 and 2020, there is no difference between the number of shares used to calculate basic and diluted loss per share. The potential shares of common stock that were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Convertible preferred stock — 18,488 — 18,488 Founder awards where performance has been met 90 — 90 — Stock options 4,830 4,036 4,830 4,036 Total 4,920 22,524 4,920 22,524 Founder awards where performance has not been met of 1,710 are excluded from the above table because the stock-price hurdles had not been met as of September 30, 2021.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSNone.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation—The unaudited condensed consolidated financial statements include the accounts of the Company and subsidiaries over which the Company has control. All intercompany transactions and balances have been eliminated.
Basis of Presentation and Accounting Principles	Basis of Presentation —The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) from the Company’s accounting records and reflect the consolidated financial position and results of operations for the three and nine months ended September 30, 2021 and 2020. Unless otherwise specified, all dollar amounts are referred to in thousands. The unaudited condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such SEC rules. We believe that the disclosures made are adequate to make the information presented not misleading. In our opinion, all adjustments considered necessary for a fair presentation of the financial statements have been included, and all adjustments are of a normal and recurring nature. We consistently applied the accounting policies consistent with the annual consolidated financial statements elsewhere in this this Quarterly Report on Form 10-Q, in preparing these unaudited condensed consolidated financial statements, with the exception of accounting standard updates described in Note 2, “Recently Adopted Accounting Pronouncements.” These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes for the fiscal year ended December 31, 2020 included in the final prospectus Accounting Principles —The financial statements and accompanying notes are prepared in accordance with generally accepted accounting principles in the United States of America (GAAP).
Use of Estimates	Use of Estimates— The preparation of unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant estimates and assumptions reflected in the consolidated financial statements include, but are not limited to, useful lives of property and equipment, valuation of deferred tax assets and liabilities, stock-based compensation, common stock valuation, operating lease right-of-use assets and liabilities, capitalization of internally developed software and associated useful lives and contingent liabilities. Actual results may differ materially from such estimates. Management believes that the estimates, and judgments upon which they rely, are reasonable based upon information available to them at the time that these estimates and judgments are made. To the extent that there are material differences between these estimates and actual results, the Company’s consolidated financial statements will be affected.
Deferred Offering Costs	Deferred Offering Costs— Deferred offering costs, which consist of direct incremental legal, accounting, and consulting fees relating to the IPO, are capitalized. Deferred offering costs of $4,865 were offset against IPO proceeds upon the consummation of the IPO, of which $1,123 are expected to be paid in the fourth quarter of 2021. This amount was included in the unaudited condensed consolidated balance sheets within Accrued expenses and other current liabilities at September 30, 2021.
Cash and Cash Equivalents	Cash and Cash Equivalents—Cash consists primarily of cash on hand and bank deposits. Cash equivalents consist primarily of money market accounts with maturities of three months or less at the date of acquisition and are stated at cost, which approximates fair value. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times.The Money market funds are considered Level 1 financial assets. Level 1 financial assets use inputs that are the unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date.
Advertising Costs	Advertising Costs— Advertising costs were approximately $12,013 and $31,764 for the three and nine months ended September 30, 2021 and $8,843 and $19,338 for the three and nine months ended
Income Taxes	Income Taxes— The Company’s provision for income taxes is computed by using an estimate of the annual effective tax rate, adjusted for discrete items taken into account in the relevant period, if any. Each quarter, the annual effective income tax rate is recomputed and if there are material changes in the estimate, a cumulative adjustment is made.
Contributors	Contributors— On March 10, 2021, the Company announced that it was ending its non-employee volunteer program, which began in 2013 to build and improve language courses. As part of this change, those contributors who participated in the program became eligible to receive a one-time award, up to an aggregate amount of approximately $5,098, including fees paid to process payments of approximately $526. The Company accounted for this under Financial Accounting Standards Board (“FASB”) Accounting Standards Codifications (“ASC”) 958-720, Not-For-Profit Entities - Other Expenses and ASC 720-25, Contributions Made
Concentration of Credit Risk	Concentration of Credit Risk —The Company’s concentration of credit risk relates to financial institutions holding the Company’s cash and cash equivalents and platforms with significant accounts receivable balances and revenue transactions. The Company maintains cash deposits with financial institutions that may exceed federally insured limits at times. Management believes that the financial institutions that hold the Company’s deposits are financially credit worthy and, accordingly, minimal credit risk exists with respect to those balances. The majority of our revenue comes through our subscriptions and advertising streams and payments are made to Duolingo through service providers. The top three, Apple, Google, and Stripe, accounted for 49.8%, 29.0%, and 14.4% of total accounts receivable as of September 30, 2021, respectively. The top three service providers, Apple, Google and Stripe, accounted for 47.8%, 28.9% and 13.8% of total accounts receivable as of December 31, 2020, respectively. Three service providers, Apple, Google, and Stripe, processed 51.6%, 29.3% and 12.1% and 51.2%, 29.0%, and 11.0% of total revenue for the three and nine months ended September 30, 2021, respectively. Three service providers, Apple, Google, and Stripe, processed 50.7%, 25.6%, and 11.0% of total revenue for the three months ended September 30, 2020, respectively. Two services providers, Apple and Google, processed 51.5% and 26.8% for the nine months ended September 30, 2020.
Share-Based Compensation	Stock-Based Compensation —The Company accounts for equity-based compensation using the fair value method as set forth in the ASC 718, Compensation—Stock Compensation , which requires the measurement and recognition of compensation expense for all stock-based payment awards based on estimated fair values. This method requires companies to estimate the fair value of stock-based compensation on the date of grant using an option pricing model. The Company estimates the fair value of each equity-based payment award on the date of grant using the Black-Scholes pricing model. The Black-Scholes model determines the fair value of equity-based payment awards based on the fair value of the underlying common stock on the date of grant and requires the use of estimates and assumptions, including the fair value of the Company’s common stock, exercise price of the stock option, expected volatility, expected life, risk-free interest rate and dividend rate. The Company estimates the expected volatility of its stock options by taking the average historical volatility of a group of comparable publicly traded companies over a period equal to the expected life of the options; it is not practical for the Company to estimate its own volatility due to the lack of historical prices. The expected term of the options is determined in accordance with existing equity agreements as the underlying options are assumed to be exercised upon the passage of time. The risk-free interest rate is the estimated average interest rate based on US Treasury zero-coupon notes with terms consistent with the expected life of the awards. The expected dividend yield is zero as the Company does not anticipate paying any recurring cash dividends in the foreseeable future. The Company accounts for forfeitures as they occur. Restricted Stock Units (RSUs) The Company began to grant RSUs in November 2020. The fair value of RSUs is estimated based on the fair value of the Company’s common stock on the date of grant. Each RSU award granted prior to the IPO vests based upon the satisfaction, during the term of the RSUs, of two requirements: length of service and a liquidity event defined as a change in control or a qualified IPO. The service-based vesting condition for the majority of these awards is satisfied over four years. The liquidity-based vesting condition is satisfied upon the occurrence of a qualifying liquidity event. The Company measures and recognizes compensation expense for all stock-based awards based on the estimated fair value of the award. Prior to July 30, 2021, no stock-based compensation expense had been recognized for RSUs because the liquidity-based vesting condition had not been probable of being satisfied. Upon the IPO, the liquidity-based vesting condition was satisfied and $2,035 of stock-based compensation expense was recognized related to these awards during the three months ended September 30, 2021. Of that amount, $1,332, $210 and $493 was included within Research and development, Sales and marketing and General and administrative, respectively, in the unaudited condensed consolidated statement of operations and comprehensive loss. Performance-based RSUs In June 2021, the Company granted 1,800 (one million eight-hundred thousand) performance-based RSUs to the Company’s founders (“Founder Awards”). The Founder Awards are divided into ten equal tranches with each tranche becoming eligible to vest upon achievement of the specified stock-price hurdles. The Founder Awards vest upon the satisfaction of both a service-based condition and a performance-based condition and generally are settled one year after vesting. The service-based condition is satisfied as to 25% of the Founder Awards on each anniversary of the completion of the IPO, subject to the continuous service of the founders through the applicable date. The fair value of the Founder Awards is determined using a Monte Carlo simulation model. The associated stock-based compensation is recorded over the derived service period, using the accelerated attribution method. If the stock-price hurdles are met sooner than the requisite service period, the stock-based compensation expense will be adjusted to prospectively recognize the remaining expense over the remaining derived service period. Provided that the founders continue to provide services to us, stock-based compensation expense is recognized over the derived service period, regardless of whether the stock-price hurdles are achieved. The first tranche was met during the three months ended September 30, 2021. The Company recognized $8,267 of stock-based compensation expense related to these awards, which is included within General and administrative in the unaudited condensed consolidated statement of operations and comprehensive loss.
Recently Adopted Accounting Pronouncements/Recently Issued Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements In August 2018, the FASB issued Accounting Standard Update (“ASU”) No. 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract (ASU 2018-15) . ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The Company adopted this guidance on January 1, 2021 and it did not have a material impact on its unaudited condensed consolidated financial statements and related disclosures upon adoption. Recently Issued Pronouncements Not Yet Adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes
Revenue	The Company has three predominant sources of revenue; time-based subscriptions, in-app advertising placement by third parties, and the Duolingo English Test. Revenue is recognized upon transfer of control of promised products or services to users in an amount that reflects the consideration the Company expects to receive in exchange for those services. The Company does not enter into contracts with a customer that contain multiple promises that result in multiple performance obligations. Revenue is recorded net of taxes assessed by a government authority that are both imposed on and concurrent with specific revenue transactions between us and our users. Revenue from time-based subscriptions includes a stand-ready obligation to provide hosting services that are consumed by the customer over the subscription period. Users can purchase Duolingo monthly or they can purchase a six-month or year-long subscription and pay for the subscription at the time of purchase. Under the year-long subscription, users can also purchase a single plan or a family plan, which allows up to six users to be on one subscription. Therefore, such payments are initially recorded to deferred revenue. The user has the ability to download limited content offline. However, as there is a significant level of integration and interdependency with the online functionality, the Company considers the service to be a single performance obligation for the online and offline content. The Company enters into arrangements with advertising networks to monetize the in-app advertising inventory. Revenue from in-app advertising placement is recognized at a point in time when the advertisement is placed and is based upon the amount received. Duolingo English Test revenue is generally recognized once the tests have gone through the proctoring process and a certification decision has been made. This process usually takes less than 48 hours after the test has been completed and uploaded. Customers have 90 days from the date of purchase to take the exam or their purchase will expire and revenue will be recognized. Virtually all customers complete their exams prior to expiration. Sometimes organizations may purchase tests in bulk via coupons with a one year expiration date. The Company will defer revenue from all tests that haven’t been proctored nor expired. The Company’s users have the option to purchase consumable in-app virtual goods. The Company recognizes revenue over the period in which the user consumes the virtual good, which is generally within a month. Principal Agent Considerations —The Company makes its application available to be downloaded through third-party digital distribution service providers. Users who purchase subscriptions also pay through the respective app stores. The Company evaluates the purchases via third-party payment processors to determine whether its revenues should be reported gross or net of fees retained by the payment processor. The Company is the principal in the transaction with the end user as a result of controlling, hosting, and integrating the delivery of the virtual items to the end user. The Company records revenue gross as a principal and records fees paid to third-party payment processors as Cost of revenues. Contract Balances —Deferred revenue mostly consists of payments we receive in advance of revenue recognition, and is mostly related to time-based subscriptions, which will be recognized into revenue over the course of the upcoming year (recognized over 12 months or less). Additionally, the Duolingo English Test has deferred revenue related to tests that have been purchased, but will not be recognized until the tests have been proctored. Disaggregation of Revenue In accordance with ASC 606, Revenue from Contracts with Customers , the Company disaggregates revenue from contracts with customers into source of revenue, which most closely depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents	The following table shows the breakout between cash and money market funds. September 30, December 31, Cash $ 39,694 $ 20,428 Money market funds 509,746 100,062 Total $ 549,440 $ 120,490

REVENUE (Tables)

REVENUE (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Schedule of Revenue Sources and Streams	Information regarding source of revenues: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Over time $ 46,030 $ 32,317 $ 129,587 $ 82,762 Point in time 17,565 12,988 48,171 30,666 Total revenue $ 63,595 $ 45,305 $ 177,758 $ 113,428 Information regarding revenue by stream: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Revenues: Subscription $ 46,030 $ 32,317 $ 129,587 $ 82,762 Advertising 9,029 6,720 27,360 18,536 Duolingo English Test 6,695 5,607 16,563 10,958 Other (1) 1,841 661 4,248 1,172 Total revenues $ 63,595 $ 45,305 $ 177,758 $ 113,428 ________________ (1) Other revenue is mainly comprised of in-app purchases of virtual goods.
Schedule of Deferred Revenues	Changes in deferred revenues were as follows: Nine Months Ended September 30, 2021 2020 Beginning balance—January 1 $ 54,792 $ 26,307 Amount from beginning balance recognized into revenue (51,254) (24,848) Recognition of deferred revenue (83,088) (59,495) Deferral of revenue 160,010 104,032 Ending balance—September 30 $ 80,460 $ 45,996

PROPERTY and EQUIPMENT, net (Ta

PROPERTY and EQUIPMENT, net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property and equipment consists of the following as of September 30, 2021 and December 31, 2020: September 30, December 31, Leasehold improvements $ 9,862 $ 7,536 Furniture, fixtures and equipment 2,699 1,959 Total property and equipment 12,561 9,495 Less: accumulated depreciation (4,551) (3,067) Total property and equipment, net $ 8,010 $ 6,428

CAPITALIZED SOFTWARE, net (Tabl

CAPITALIZED SOFTWARE, net (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Capitalized Software	Capitalized software consists of the following as of September 30, 2021 and December 31, 2020: September 30, December 31, Capitalized software $ 10,553 $ 8,181 Less: accumulated amortization (6,369) (5,885) Capitalized software, net $ 4,184 $ 2,296
Finite-lived Intangible Assets Amortization Expense	Amortization expense is included within the following financial statement line items within the Company’s consolidated statement of operations and comprehensive loss: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Cost of revenues $ — $ 26 $ — $ 77 Sales and marketing 188 148 484 399 Total $ 188 $ 174 $ 484 $ 476

CONVERTIBLE PREFERRED STOCK (Ta

CONVERTIBLE PREFERRED STOCK (Tables)	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
Temporary Equity	The following table summarizes the convertible preferred stock outstanding immediately prior to the conversion into common stock and as of December 31, 2020: Shares Series Authorized Outstanding Per share price Aggregate liquidation preference Funds received Fees incurred Carrying value of convertible preferred stock A 3,865 3,865 $ 0.85 $ 3,300 $ 3,300 $ 52 $ 3,248 B 6,298 6,298 2.38 15,000 15,000 60 14,940 C 2,948 2,948 6.78 20,000 20,000 112 19,888 D 3,154 3,154 14.27 45,000 45,000 146 44,853 E 1,224 1,224 20.43 25,000 25,000 92 24,909 F 758 758 39.57 30,000 30,000 153 29,848 G 241 241 41.38 10,000 10,000 24 9,976 H 586 586 59.77 35,000 35,000 52 34,947 Total 19,074 19,074 $ 183,300 $ 183,300 $ 691 $ 182,609

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Share-based Payment Arrangement, Option, Activity	Stock option activity as of September 30, 2021 is set forth below: Number of Weighted- Weighted- average remaining contractual life (years) Aggregate intrinsic value Options outstanding at January 1, 2021 8,365 $ 10.68 7.47 $ 230,596 Granted 72 52.80 Exercised (1,134) 6.45 Repurchased (220) 4.81 Forfeited and expired (59) 13.43 Options outstanding at September 30, 2021 7,024 $ 11.94 7.01 $ 1,084,464 Options exercisable at September 30, 2021 4,830 $ 9.79 6.42 $ 756,259
Share-based Payment Arrangement, RSU, Activity	RSU activity for the nine months ended September 30, 2021 is set forth below: Restricted stock units Weighted- Outstanding at January 1, 2021 34 $ 38.08 Granted 671 66.43 Vested — — Forfeited (5) 106.59 Outstanding at September 30, 2021 700 $ 64.77
Share-based Payment Arrangement, Payment Award	Tranche Company Stock Price Hurdle Number of RSUs Eligible to Vest 1 $ 127.50 90 2 $ 153.00 90 3 $ 178.50 90 4 $ 204.00 180 5 $ 255.00 180 6 $ 306.00 180 7 $ 357.00 180 8 $ 408.00 180 9 $ 612.00 270 10 $ 816.00 360
Share-based Payment Arrangement, Expensed, Amount	Stock based compensation expense is included in the consolidated statements of operations as shown in the following table: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Cost of revenues $ 6 $ 3 $ 8 $ 4 Research and development 3,533 526 5,749 1,505 Sales and marketing 408 116 548 296 General and administrative 16,715 1,037 19,815 2,712 Total $ 20,662 $ 1,682 $ 26,120 $ 4,517

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2021
Other Liabilities Disclosure [Abstract]
Schedule of Accrued Liabilities and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: September 30, December 31, Sales and VAT tax accrual $ 2,289 $ 2,301 Obligations under current leases 1,542 1,111 Employee related benefits 1,143 889 Marketing related accruals 1,086 1,513 Other 3,392 2,820 Total $ 9,452 $ 8,634

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Three Months Ended September 30, Nine Months Ended September 30, (In thousands, except per share data) 2021 2020 2021 2020 Numerator: Net loss attributable to Class A and Class B common shareholders $ (28,970) $ (3,176) $ (42,618) $ (5,369) Denominator: Weighted-average shares in computing net loss per share attributable to Class A and Class B common stockholders, basic and diluted 29,531 12,530 18,600 12,471 Basic loss per common share $ (0.98) $ (0.25) $ (2.29) $ (0.43) Diluted loss per common share $ (0.98) $ (0.25) $ (2.29) $ (0.43)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The potential shares of common stock that were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive are as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Convertible preferred stock — 18,488 — 18,488 Founder awards where performance has been met 90 — 90 — Stock options 4,830 4,036 4,830 4,036 Total 4,920 22,524 4,920 22,524

DESCRIPTION OF THE BUSINESS A_2

DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION (Details) $ / shares in Units, $ in Thousands	Jul. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Jul. 15, 2021shares	Dec. 31, 2020USD ($)shares
Business And Organization [Line Items]
Issuance of common stock in connection with the initial public offering, net of underwriting discounts and issuance costs | $	$ 455,532	$ 426,191	$ 0
Conversion ratio	1
Common stock carrying value | $		$ 4			$ 1
Common stock, shares outstanding (in shares)					12,794,000
Common Class A
Business And Organization [Line Items]
Common stock, shares outstanding (in shares)		12,847,000
Common Class A | IPO
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	5,872,000
Sale of stock, price per share (in usd per share) | $ / shares	$ 102
Common Class A | IPO | Stockholders
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	1,406,000
Common Class A | IPO | Duolingo
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	4,466,000
Common Class A | Over-Allotment Option
Business And Organization [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	766,000
Common Class B
Business And Organization [Line Items]
Convertible preferred stock, shares issued upon conversion (in shares)	19,074,000
Conversion ratio	1
Common stock carrying value | $	$ 182,609
Common stock, shares outstanding (in shares)		24,598,000
Common Class B | Founders
Business And Organization [Line Items]
Common stock, shares outstanding (in shares)				6,930,000

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 549,440	$ 120,490
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	39,694	20,428
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 509,746	$ 100,062

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	Sep. 30, 2021USD ($)tranche	Mar. 10, 2021USD ($)	Dec. 31, 2020	Sep. 30, 2021USD ($)tranche	Jun. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)tranche	Sep. 30, 2020USD ($)	Jul. 30, 2021USD ($)
Concentration Risk [Line Items]
Deferred offering costs reclassified to stockholders equity									$ 4,865,000
Deferred offering costs incurred but not yet paid				$ 1,123,000
Advertising costs				12,013,000		$ 8,843,000	$ 31,764,000	$ 19,338,000
Volunteer program, one-time payment to contributors	$ 4,220,000	$ 5,098,000		4,220,000			4,220,000
Volunteer program, transaction fees		$ 526,000
Volunteer program award reserve					$ (878,000)
Compensation expense				20,662,000		1,682,000	26,120,000	4,517,000
Sales and marketing
Concentration Risk [Line Items]
Compensation expense				408,000		116,000	548,000	296,000
General and administrative
Concentration Risk [Line Items]
Compensation expense				16,715,000		1,037,000	19,815,000	2,712,000
Research and development
Concentration Risk [Line Items]
Compensation expense				3,533,000		$ 526,000	$ 5,749,000	$ 1,505,000
Restricted Stock Units (RSUs)
Concentration Risk [Line Items]
Compensation expense				2,035,000
Restricted Stock Units (RSUs) | Sales and marketing
Concentration Risk [Line Items]
Compensation expense				210,000
Restricted Stock Units (RSUs) | General and administrative
Concentration Risk [Line Items]
Compensation expense				493,000
Restricted Stock Units (RSUs) | Research and development
Concentration Risk [Line Items]
Compensation expense				$ 1,332,000
Performance Based RSUs | Founders
Concentration Risk [Line Items]
Number of tranches | tranche	10			10			10
Performance Based RSUs | Tranche One
Concentration Risk [Line Items]
Compensation expense				$ 8,267,000
Accounts Receivable | Customer Concentration Risk | Apple
Concentration Risk [Line Items]
Concentration risk, percentage	49.80%		47.80%
Accounts Receivable | Customer Concentration Risk | Google
Concentration Risk [Line Items]
Concentration risk, percentage	29.00%		28.90%
Accounts Receivable | Customer Concentration Risk | Stripe
Concentration Risk [Line Items]
Concentration risk, percentage	14.40%		13.80%
Revenue Benchmark | Customer Concentration Risk | Apple
Concentration Risk [Line Items]
Concentration risk, percentage				51.60%		50.70%	51.20%	51.50%
Revenue Benchmark | Customer Concentration Risk | Google
Concentration Risk [Line Items]
Concentration risk, percentage				29.30%		25.60%	29.00%	26.80%
Revenue Benchmark | Customer Concentration Risk | Stripe
Concentration Risk [Line Items]
Concentration risk, percentage				12.10%		11.00%	11.00%

REVENUE - Disaggregation of Rev

REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 63,595	$ 45,305	$ 177,758	$ 113,428
Subscription
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	46,030	32,317	129,587	82,762
Advertising
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	9,029	6,720	27,360	18,536
Duolingo English Test
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	6,695	5,607	16,563	10,958
Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,841	661	4,248	1,172
Over time
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	46,030	32,317	129,587	82,762
Point in time
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 17,565	$ 12,988	$ 48,171	$ 30,666

REVENUE - Deferred Revenue Roll

REVENUE - Deferred Revenue Rollforward (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Revenue from Contract with Customer, Liability [Roll Forward]
Beginning balance	$ 54,792	$ 26,307
Amount from beginning balance recognized into revenue	(51,254)	(24,848)
Recognition of deferred revenue	(83,088)	(59,495)
Deferral of revenue	160,010	104,032
Ending balance	$ 80,460	$ 45,996

PROPERTY and EQUIPMENT, net (De

PROPERTY and EQUIPMENT, net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 12,561		$ 12,561		$ 9,495
Less: accumulated depreciation	(4,551)		(4,551)		(3,067)
Total property and equipment, net	8,010		8,010		6,428
Depreciation expense	545	$ 453	1,485	$ 1,173
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,862		9,862		7,536
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,699		$ 2,699		$ 1,959

CAPITALIZED SOFTWARE, net - Cap

CAPITALIZED SOFTWARE, net - Capitalized Software (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Capitalized software	$ 10,553	$ 8,181
Less: accumulated amortization	(6,369)	(5,885)
Capitalized software, net	$ 4,184	$ 2,296

CAPITALIZED SOFTWARE, net - Nar

CAPITALIZED SOFTWARE, net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of capitalized computer software	$ 188	$ 174	$ 484	$ 476

CAPITALIZED SOFTWARE, net - Sch

CAPITALIZED SOFTWARE, net - Schedule of Capitalized Software Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Amortization of capitalized computer software	$ 188	$ 174	$ 484	$ 476
Cost of revenues
Finite-Lived Intangible Assets [Line Items]
Amortization of capitalized computer software	0	26	0	77
Sales and marketing
Finite-Lived Intangible Assets [Line Items]
Amortization of capitalized computer software	$ 188	$ 148	$ 484	$ 399

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
PAETR	(0.20%)	(0.70%)	(0.20%)	(0.80%)
Income tax expense	$ 51	$ 23	$ 69	$ 45
Pretax income (loss)	$ (28,919)	$ (3,153)	$ (42,549)	$ (5,324)

CONVERTIBLE PREFERRED STOCK - S

CONVERTIBLE PREFERRED STOCK - Schedule of Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2021	Jul. 29, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Authorized (in shares)		19,074,000		19,074,000
Outstanding (in shares)	0	19,074,000	19,074,000	19,074,000	18,488,000	18,488,000	18,247,000
Aggregate liquidation preference		$ 183,300		$ 183,300
Funds received		183,300		183,300
Fees incurred		691		691
Carrying value of convertible preferred stock	$ 0	$ 182,609	$ 182,609	$ 182,609	$ 147,662	$ 147,662	$ 137,686
A
Temporary Equity [Line Items]
Authorized (in shares)		3,865,000		3,865,000
Outstanding (in shares)		3,865,000		3,865,000
Per share price at issuance (in usd per share)		$ 0.85		$ 0.85
Aggregate liquidation preference		$ 3,300		$ 3,300
Funds received		3,300		3,300
Fees incurred		52		52
Carrying value of convertible preferred stock		$ 3,248		$ 3,248
B
Temporary Equity [Line Items]
Authorized (in shares)		6,298,000		6,298,000
Outstanding (in shares)		6,298,000		6,298,000
Per share price at issuance (in usd per share)		$ 2.38		$ 2.38
Aggregate liquidation preference		$ 15,000		$ 15,000
Funds received		15,000		15,000
Fees incurred		60		60
Carrying value of convertible preferred stock		$ 14,940		$ 14,940
C
Temporary Equity [Line Items]
Authorized (in shares)		2,948,000		2,948,000
Outstanding (in shares)		2,948,000		2,948,000
Per share price at issuance (in usd per share)		$ 6.78		$ 6.78
Aggregate liquidation preference		$ 20,000		$ 20,000
Funds received		20,000		20,000
Fees incurred		112		112
Carrying value of convertible preferred stock		$ 19,888		$ 19,888
D
Temporary Equity [Line Items]
Authorized (in shares)		3,154,000		3,154,000
Outstanding (in shares)		3,154,000		3,154,000
Per share price at issuance (in usd per share)		$ 14.27
Aggregate liquidation preference		$ 45,000		$ 45,000
Funds received		45,000		45,000
Fees incurred		146		146
Carrying value of convertible preferred stock		$ 44,853		$ 44,853
E
Temporary Equity [Line Items]
Authorized (in shares)		1,224,000		1,224,000
Outstanding (in shares)		1,224,000		1,224,000
Per share price at issuance (in usd per share)		$ 20.43		$ 20.43
Aggregate liquidation preference		$ 25,000		$ 25,000
Funds received		25,000		25,000
Fees incurred		92		92
Carrying value of convertible preferred stock		$ 24,909		$ 24,909
F
Temporary Equity [Line Items]
Authorized (in shares)		758,000
Outstanding (in shares)		758,000		758,000
Per share price at issuance (in usd per share)		$ 39.57		$ 39.57
Aggregate liquidation preference		$ 30,000		$ 30,000
Funds received		30,000		30,000
Fees incurred		153		153
Carrying value of convertible preferred stock		$ 29,848		$ 29,848
G
Temporary Equity [Line Items]
Authorized (in shares)		241,000		241,000
Outstanding (in shares)		241,000		241,000
Per share price at issuance (in usd per share)		$ 41.38		$ 41.38
Aggregate liquidation preference		$ 10,000		$ 10,000
Funds received		10,000		10,000
Fees incurred		24		24
Carrying value of convertible preferred stock		$ 9,976		$ 9,976
H
Temporary Equity [Line Items]
Authorized (in shares)		586,000		586,000
Outstanding (in shares)		586,000		586,000
Per share price at issuance (in usd per share)		$ 59.77		$ 59.77
Aggregate liquidation preference		$ 35,000		$ 35,000
Funds received		35,000		35,000
Fees incurred		52		52
Carrying value of convertible preferred stock		$ 34,947		$ 34,947

CONVERTIBLE PREFERRED STOCK - N

CONVERTIBLE PREFERRED STOCK - Narrative (Details) shares in Thousands, $ in Thousands	Sep. 30, 2021USD ($)	Jul. 30, 2021USD ($)shares	Dec. 31, 2020USD ($)
Temporary Equity [Line Items]
Conversion ratio		1
Common stock carrying value	$ 4		$ 1
Common Class B
Temporary Equity [Line Items]
Preferred stock outstanding | shares		19,074
Conversion ratio		1
Common stock carrying value		$ 182,609

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2021shares	Feb. 28, 2021USD ($)$ / sharesshares	Sep. 30, 2021USD ($)dayshares	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)trancheday$ / sharesshares	Sep. 30, 2020USD ($)	Jul. 30, 2021$ / shares	Jul. 26, 2021shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value, exercised					$ 102,628
Compensation expense			$ 20,662	$ 1,682	26,120	$ 4,517
Unrecognized compensation cost, options			15,857		15,857
Unrecognized compensation cost			$ 56,249		$ 56,249
Closing trading price, specified calendar | day			60		60
Fair market value of share price (in usd per share) | $ / shares		$ 38.08
Payments for repurchase of stock options					$ 7,335	$ 0
Options repurchased					7,335
Common stock repurchased and retired					868
Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options repurchased					7,335
Common stock repurchased and retired					868
Tender Offer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense		$ 5,275
Sale Of Stock, Percentage Sold, Maximum		0.10
Sale of stock, price per share (in usd per share) | $ / shares		$ 59.77
Payments for repurchase of stock options		$ 13,479
Options recycled back into option pool (in shares) | shares		220
Common stock repurchased and retired (in shares) | shares		23
Common stock repurchased and retired		$ 868
Tender Offer | Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options repurchased		$ 7,335
IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense			$ 5,574
IPO | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock, price per share (in usd per share) | $ / shares							$ 102
Performance Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense, excluding options			110,817		$ 110,817
Performance Based RSUs | Share-Based Payment Arrangement, Founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in usd per share) | $ / shares					$ 61.56
Performance Based RSUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award service period					3 years 6 months 29 days
Performance Based RSUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award service period					5 years 11 months 1 day
Performance Based RSUs | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense			$ 8,267
Performance Based RSUs | Founders
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments other than options, grants in period (in shares) | shares	1,800
Settlement period after vesting	1 year
Award vesting percentage	25.00%
Number of tranches | tranche					10
Award service period	10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, weighted-average period of recognition					2 years
Number of options available for grant (in shares) | shares			7,842		7,842
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense			$ 2,035
Unrecognized compensation cost, weighted-average period of recognition					4 years
Unrecognized compensation expense, excluding options			$ 40,392		$ 40,392
Equity instruments other than options, grants in period (in shares) | shares					671
2011 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
Share-based compensation, term of award					10 years
Incentive stock options, minimum exercise price, percent					100.00%
2021 Plan | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) | shares								7,946
Employee Stock Purchase Plan | Common Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares) | shares								1,119

STOCK-BASED COMPENSATION - Stoc

STOCK-BASED COMPENSATION - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Number of options
Outstanding, beginning balance (in shares) | shares	8,365
Granted (in shares) | shares	72
Exercised (in shares) | shares	(1,134)
Repurchased (in shares) | shares	(220)
Forfeited and expired (in shares) | shares	(59)
Outstanding, ending balance (in shares) | shares	7,024	8,365
Number of shares exercisable (in shares) | shares	4,830
Weighted Average Exercise Price
Outstanding, beginning balance (in usd per share) | $ / shares	$ 10.68
Granted (in usd per share) | $ / shares	52.80
Exercised (in usd per share) | $ / shares	6.45
Repurchased (in usd per share) | $ / shares	4.81
Forfeited and expired (in usd per share) | $ / shares	13.43
Outstanding, ending balance (in usd per share) | $ / shares	11.94	$ 10.68
Weighted average exercise price, exercisable (in usd per share) | $ / shares	$ 9.79
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average remaining contractual term (in years), outstanding	7 years 3 days	7 years 5 months 19 days
Weighted average remaining contractual term (in years), exercisable	6 years 5 months 1 day
Aggregate intrinsic value, outstanding | $	$ 1,084,464	$ 230,596
Aggregate intrinsic value, exercisable | $	$ 756,259

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) - $ / shares shares in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Restricted stock units
Beginning balance (in shares)	700	34
Granted (in shares)	671
Vested (in shares)	0
Forfeited (in shares)	(5)
Ending balance (in shares)	700
Weighted- average grant date fair value per share
Beginning balance (in usd per share)	$ 38.08
Granted (in usd per share)	66.43
Vested (in usd per share)	0
Forfeited (in shares)	106.59
Ending balance (in usd per share)	$ 64.77

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Payment Award (Details) - Restricted Stock Units (RSUs)	Sep. 30, 2021$ / sharesshares
Tranche 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 127.50
Number of RSUs Eligible to Vest (in shares) | shares	90,000
Tranche 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 153
Number of RSUs Eligible to Vest (in shares) | shares	90,000
Tranche 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 178.50
Number of RSUs Eligible to Vest (in shares) | shares	90,000
Tranche 4
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 204
Number of RSUs Eligible to Vest (in shares) | shares	180,000
Tranche 5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 255
Number of RSUs Eligible to Vest (in shares) | shares	180,000
Tranche 6
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 306
Number of RSUs Eligible to Vest (in shares) | shares	180,000
Tranche 7
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 357
Number of RSUs Eligible to Vest (in shares) | shares	180,000
Tranche 8
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 408
Number of RSUs Eligible to Vest (in shares) | shares	180,000
Tranche 9
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 612
Number of RSUs Eligible to Vest (in shares) | shares	270,000
Tranche 10
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company Stock Price Hurdle (in usd per share) | $ / shares	$ 816
Number of RSUs Eligible to Vest (in shares) | shares	360,000

STOCK-BASED COMPENSATION - Sc_3

STOCK-BASED COMPENSATION - Schedule of Income Statement Location for Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 20,662	$ 1,682	$ 26,120	$ 4,517
Cost of revenues
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	6	3	8	4
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	3,533	526	5,749	1,505
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	408	116	548	296
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense	$ 16,715	$ 1,037	$ 19,815	$ 2,712

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Other Liabilities Disclosure [Abstract]
Sales and VAT tax accrual	$ 2,289	$ 2,301
Operating lease, liability, current, statement of financial position, extensible enumeration	Total	Total
Obligations under current leases	$ 1,542	$ 1,111
Employee related benefits	1,143	889
Marketing related accruals	1,086	1,513
Other	3,392	2,820
Total	$ 9,452	$ 8,634

EMPLOYEE BENEFIT PLAN (Details)

EMPLOYEE BENEFIT PLAN (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, contributions by employer	$ 877	$ 495	$ 2,360	$ 1,308
First 4% Of Employee Elective Deferral
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match			100.00%	100.00%
Employer matching contribution, percent of employees' gross pay			4.00%	3.00%
Next 2% Of Employee Elective Deferral
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match			50.00%	50.00%
Employer matching contribution, percent of employees' gross pay			2.00%	2.00%

EARNINGS PER SHARE - Schedule o

EARNINGS PER SHARE - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss attributable to Class A and Class B common shareholders	$ (28,970)	$ (3,176)	$ (42,618)	$ (5,369)
Denominator:
Weighted-average shares in computing net loss per share attributable to Class A and Class B common stockholders, basic (in shares)	29,531	12,530	18,600	12,471
Weighted-average shares in computing net loss per share attributable to Class A and Class B common stockholders, diluted (in shares)	29,531	12,530	18,600	12,471
Basic loss per common share (in usd per share)	$ (0.98)	$ (0.25)	$ (2.29)	$ (0.43)
Diluted loss per common share (in usd per share)	$ (0.98)	$ (0.25)	$ (2.29)	$ (0.43)

EARNINGS PER SHARE - Schedule_2

EARNINGS PER SHARE - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	4,920,000	22,524,000	4,920,000	22,524,000
Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	0	18,488,000	0	18,488,000
Founder awards where performance has been met
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	90,000	0	90,000	0
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	4,830,000	4,036,000	4,830,000	4,036,000

EARNINGS PER SHARE - Narrative

EARNINGS PER SHARE - Narrative (Details)	9 Months Ended
	Sep. 30, 2021vote_per_shareshares
Common Class A
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Voting rights, per share	1
Common Class B
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Voting rights, per share	20
Performance Based RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Founder awards where performance not met | shares	1,710,000