

	For the three months ended						For the six months ended
	June 28, 2019			June 29, 2018			June 28, 2019			June 29, 2018
Provision for (benefit of) income taxes	$	4,522		$	4,711		$	7,123		$	(1,868	)
Effective tax rates	16.2		%	20.0		%	14.6		%	(4.9		)%

For the three and six months ended June 28, 2019, and the three months ended June 29, 2018, the difference between the Company's effective tax rate and the 21% federal statutory rate resulted primarily from lower foreign tax rates, lower effective federal rates on foreign derived intangible income, research and development credits, and $1,808, $3,635, and $880 from excess benefits related to stock-based compensation. These benefits were partially offset by state taxes, foreign withholding taxes and the impact of non-deductible expenses.

For the six months ended June 29, 2018, the difference between the Company's effective tax benefit of 4.9% and the 21% federal statutory rate resulted primarily from a $9,838 one-time impact of the favorable conclusion of the 2015 U.S. Internal Revenue Service ("IRS") audit and the recognition of related tax positions with respect to the deductibility of amortization and depreciation expense resulting from the acquisition of the Company in 2008. The benefit of the deductions was not recognized in accounting for the acquisition due to uncertainty about whether the tax position would withstand audit. The results of the closing agreement with the IRS provided basis for the Company to conclude that the amortization and depreciation will be deductible for all open tax years. In addition, the effective tax rate benefited from lower foreign tax rates, lower effective federal rates on foreign derived intangible income, research and development credits, and $1,117 from excess benefits related to stock-based compensation. These benefits were partially offset by state taxes, foreign withholding taxes and the impact of non-deductible expenses.

The Company's federal tax returns for 2016 and forward, state tax returns for 2014 forward, and foreign tax returns from 2016 forward are subject to examination by tax authorities. The Company is currently under examination by the California state tax authority for 2015 and 2016.

The Company has obtained tax incentives in Switzerland that are effective on a formal basis through March 2019, and indefinitely on a statutory basis, as long as the Company's operations meet specified criteria. The effect of the tax incentive was not material to the Company's income tax provision for the three and six months ended June 28, 2019 and June 29, 2018.