less revenue from certain acquisitions. For the three-month period ended March 31, 2021, Merit’s constant currency revenue, organic, excludes revenues attributable to the acquisition of KA Medical, LLC in November 2020.
Core Revenue
Merit’s core revenue is defined, with respect to prior fiscal year periods, as GAAP revenue less revenue from certain dispositions. For the three-month period ended March 31, 2020, Merit’s core revenue excludes revenues attributable to its distribution agreement with NinePoint Medical, Inc., which was suspended during the first quarter of 2020, revenues attributable to the manufacture of Merit’s Hypotube product which were divested in August 2020, and revenues attributable to the ITL Healthcare Pty Ltd (“ITL”) procedure pack business in Australia which was closed in December 2020.
With respect to current fiscal year periods, core revenue is defined as constant currency revenue, organic (as defined above), less $0.9 million of revenue attributable to sales of the Cultura nasopharyngeal swab and test kit (which benefited from high demand in 2020 resulting from the COVID-19 pandemic but which is not expected to be a significant revenue contribution in the future), as well as $0.2 million of revenue attributable to the final sales of products from the closed ITL procedure pack business (which were carried over from the fourth quarter of 2020 to the first quarter of 2021 and are not expected to impact sales in future periods).
Non-GAAP Gross Margin
Non-GAAP gross margin is calculated by reducing GAAP cost of sales by amounts recorded for amortization of intangible assets and certain inventory write-offs, divided by reported net sales.
Non-GAAP Operating Income and Margin
Non-GAAP operating income is calculated by adjusting GAAP operating income for certain items which are deemed by Merit’s management to be outside of core operations and vary in amount and frequency among periods, such as expenses related to new acquisitions, non-cash expenses related to amortization or write-off of previously acquired tangible and intangible assets, certain severance expenses, performance-based stock compensation expenses, corporate transformation expenses, expenses resulting from non-ordinary course litigation or administrative proceedings and resulting settlements, governmental proceedings or changes in industry regulations, as well as other items set forth in the tables below. Non-GAAP operating margin is calculated by dividing non-GAAP operating income by reported net sales.
Non-GAAP Net Income
Non-GAAP net income is calculated by adjusting GAAP net income (loss) for the items set forth in the definition of non-GAAP operating margin above, as well as for expenses related to debt issuance costs, gains or losses on disposal of certain assets, changes in tax regulations, and other items set forth in the tables below.
Non-GAAP EPS
Non-GAAP EPS is defined as non-GAAP net income divided by the diluted shares outstanding for the corresponding period.
Free Cash Flow
Free cash flow is defined as cash flow from operations calculated in accordance with GAAP, less capital expenditures calculated in accordance with GAAP, as set forth in the consolidated statement of cash flows.
Non-GAAP Financial Measure Reconciliations
The following tables set forth supplemental financial data and corresponding reconciliations of non-GAAP financial measures to Merit’s corresponding financial measures prepared in accordance with GAAP, in each case, for the three-month periods ended March 31, 2021 and 2020. The non-GAAP income adjustments referenced in the following tables do not reflect non-performance-based stock compensation expense of approximately $2.6 million and $2.3 million for the three-month periods ended March 31, 2021 and 2020, respectively.