Income Taxes

6 Months Ended

Jun. 30, 2021

Income Tax Disclosure [Abstract]

Income Taxes

Income Taxes

The Company's effective income tax rate is based on estimated income for the year, the estimated composition of the income in different jurisdictions and discrete adjustments, if any, in the applicable quarterly periods. Potential discrete adjustments include tax charges or benefits related to stock-based compensation, changes in tax legislation, settlements of tax audits or assessments, uncertain tax positions and acquisitions, among other items.

In the second quarter of 2018, the Company filed an appeal with the Massachusetts Appellate Tax Board (“MATB”) contesting adverse audit findings related to certain tax benefits and exemptions. In July 2020, the MATB ruled in the Company’s favor; however, the decision is eligible for appeal by the Massachusetts Department of Revenue. The Company has determined that it is more-likely-than-not that it will ultimately prevail in the event of any such appeal. Accordingly, no reserve has been recorded related to these controversies. The Company has, however, estimated that an adverse ruling could result in a gross income tax charge of approximately $43.0 million, which may be partially offset by certain state tax credits of $30.0 million, which the Company does not currently benefit from as a result of the Company's valuation allowance assessment.

The Company’s effective income tax rate was 8.5% and 10.3% for the six months ended June 30, 2021 and 2020, respectively. The lower effective tax rate for the six months ended June 30, 2021 is primarily due to an increase in foreign income taxed at lower rates and the revaluation of certain foreign income tax liabilities due to foreign exchange rate fluctuations.

For the six months ended June 30, 2021, the effective income tax rate was lower than the federal statutory tax rate due to foreign income taxed at lower rates, the excess tax benefit related to stock-based compensation, the revaluation of certain foreign income tax liabilities due to foreign exchange rate fluctuations and the benefit of U.S. federal, state and foreign research and development credits. These amounts were partially offset by non-deductible stock-based compensation and state taxes.

For the six months ended June 30, 2020, the effective income tax rate was lower than the federal statutory tax rate due to foreign income taxed at lower rates, the excess tax benefit related to stock-based compensation and the benefit of U.S. federal, state and foreign research and development credits. These amounts were partially offset by the valuation allowance recorded against deferred tax assets related to state tax credits, non-deductible stock-based compensation and state taxes.