| Document and Entity Information | Nov. 12, 2024 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001647639 |
| Document Type | 8-K |
| Document Period End Date | Nov. 12, 2024 |
| Entity Registrant Name | Upstart Holdings, Inc. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39797 |
| Entity Tax Identification Number | 46-4332431 |
| Entity Address, Address Line One | 2950 S. Delaware Street |
| Entity Address, Address Line Two | Suite 410 |
| Entity Address, City or Town | San Mateo |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94403 |
| City Area Code | (833) |
| Local Phone Number | 212-2461 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | UPST |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
