6. Income Taxes

Income Taxes

Our effective income tax rates were 3.5% and 20.0% for the thirty-nine weeks ended September 27, 2018 and September 28, 2017, respectively. The lower effective rate for the thirty-nine weeks ended September 27, 2018 was primarily due to tax reform passed in December 2017 and the recognition of excess tax benefits related to stock options exercised.

Provisional amounts

In connection with the Tax Cuts and Jobs Act (the “Act”) passed in December 2017, we remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21% for federal income tax purposes and 3.6% currently estimated for state income tax purposes. We recorded a provisional tax benefit of $17.9 million as of December 28, 2017 related to the remeasurement of certain deferred tax balances, and we have increased this provisional tax benefit by an additional $0.6 million during the thirty-nine weeks ended September 27, 2018. However, we are still analyzing certain aspects of the Act and refining our calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts.