A reconciliation of the United States federal statutory corporate tax rate to the Company’s income tax expense, or effective tax rate, was as follows:


	Three-months Ended						Nine-months Ended
	September 27, 2020		September 29, 2019		September 27, 2020		September 29, 2019
Income tax expense at U.S. federal statutory corporate tax rate	21	%	21	%	21	%	21	%
State income taxes, net of federal benefit	1	%	1	%	1	%	1	%
Foreign tax rate differential	(5)	%	(7)	%	(5)	%	(7)	%
Tax credit	(1)	%	(1)	%	(1)	%	(1)	%

Discrete tax benefit related to stock options	(4)	%	(1)	%	(9)	%	(3)	%
Discrete tax expense (benefit) related to tax return filings	—	%	(3)	%	3	%	(1)	%

Other	2	%	2	%	2	%	2	%
Income tax expense	14	%	12	%	12	%	12	%

The Company is tax resident in numerous jurisdictions around the world and has identified its major tax jurisdictions as the United States, Ireland, and China. The statutory tax rate is 12.5% in Ireland and 25% in China, compared to the U.S. federal statutory corporate tax rate of 21%. These differences resulted in a favorable impact to the effective tax rate of 5 percentage points for both the three-month and nine-month periods ended September 27, 2020, and 7 percentage points for the same periods in 2019. Management has determined that earnings from its legal entity in China will be indefinitely reinvested to provide local funding for growth, and that earnings from all other jurisdictions will not be indefinitely reinvested.

The Company recorded discrete tax benefits arising from the difference between the deduction for tax purposes and the compensation cost recognized for financial reporting purposes from stock exercises that resulted in a favorable impact to the effective tax rate of 4 and 9 percentage points for the three-month and nine-month periods ended September 27, 2020, respectively, and 1 and 3 percentage points for the same periods in 2019. In addition, the Company recorded other discrete tax items primarily related to the final true-up of the prior year tax accrual upon

filing the related tax return that resulted in an unfavorable impact to the effective tax rate of 3 percentage points for the nine-month period ended September 27, 2020, and a favorable impact to the effective tax rate of 3 and 1 percentage points for the three-month and nine-month periods ended September 29, 2019, respectively.

Excluding the impact of these discrete items, the Company’s effective tax rate was 18% of pre-tax income for the three-month and nine-month periods ended September 27, 2020, respectively, compared to 16% for the same periods in 2019. The increase in the effective tax rate, excluding the impact of discrete items, was due to more of the Company's profits being earned and taxed in higher tax jurisdictions.

During the nine-month period ended September 27, 2020, the Company recorded a $198,000 decrease in reserves for income taxes, net of deferred tax benefit. Estimated interest and penalties included in these amounts totaled $212,000 for the nine-month period ended September 27, 2020.

The Company’s reserve for income taxes, including gross interest and penalties, was $12,353,000 as of September 27, 2020, which included $11,325,000 classified as a non-current liability and $1,028,000 recorded as an increase to a non-current deferred tax liability. The amount of gross interest and penalties included in these balances was $1,192,000. If the Company’s tax positions were sustained or the statutes of limitations related to certain positions expired, these reserves would be released and income tax expense would be reduced in a future period.

The Company has defined its major tax jurisdictions as the United States, Ireland, and China, and within the United States, Massachusetts. Within the United States, the tax years 2017 through 2019 remain open to examination by the Internal Revenue Service ("IRS") and various state tax authorities. The tax years 2016 through 2019 remain open to examination by various taxing authorities in other jurisdictions in which the Company operates. The Company has recently been notified that it is under audit by the IRS for the tax year 2017. Management believes the Company is adequately reserved for this audit.

The Company has filed its U.S. federal tax return in the fourth quarter of 2020 for tax year 2019, and as a result, is expected to record a discrete tax benefit in excess of $12,000,000 in the fourth quarter. This benefit was the result of new regulations issued by the IRS relating to the use of foreign tax credits as allowable to reduce the tax associated with foreign operations under Global Intangible Low-Taxed Income (“GILTI”). These credits were generated from taxes paid relating to the acquisition of Sualab in October 2019.