	Year Ended
	December 31,
	2020		2019
Current portion:
Federal	$	—	$	(182	)
Deferred portion:
Federal		—		182
	$	—	$	—

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.

Significant components of the Company’s deferred tax assets and liabilities were (in thousands):

	Year Ended
	December 31,
	2020			2019
Deferred tax assets:
Federal and state loss carryforwards	$	3,031		$	1,697
Reserves, accruals and other		239			156
Depreciation and amortization		1,284			1,629
Deferred stock-based compensation		2,698			2,613
Research and development credit carryforwards		6,613			6,707
Foreign tax and other credits		-			61
Total deferred tax assets		13,865			12,863
Less: Valuation allowance		(13,865	)		(12,802	)
Net deferred tax assets	$	—		$	61

The $1.1 million increase in the valuation allowance during 2020 was primarily the result of an increase to the net operating loss carryforwards for the current year. The valuation allowance increased by $0.9 million during the year ended December 31, 2019.

Utilization of the Company’s net operating losses (NOLs) and tax credit carryforwards is subject to a substantial annual limitation due to the ownership change limitations provided by the IRC and similar state provisions. Section 382 of the IRC (Section 382) imposes limitations on a corporation’s ability to utilize its NOL and tax credit carryforwards, if it experiences an “ownership change.” In general terms, an ownership change may result from transactions increasing the ownership percentage of certain stockholders in the stock of the corporation by more than 50% over a three-year period. In the event of an ownership change, utilization of the NOLs would be subject to an annual limitation under Section 382 determined by multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate. While a formal study has not been performed, the Company believes that a Section 382 ownership change occurred as a result of a financing effected in October 2018. The Company believes this Section 382 limitation will result in approximately 97% of the federal and state NOLs expiring before they can be utilized, and approximately 96% of the federal tax credit carryforwards expiring before they can be utilized.

As of December 31, 2020, the Company had NOLs of approximately $205.2 million for federal income tax purposes and approximately $127.0 million for state income tax purposes. Only approximately $11.3 million of the federal NOLs and $9.5 million of the state NOLs are expected to be available before expiration due to the Section 382 limitation. These NOLs are available to reduce future taxable income and will expire at various times from 2025 through 2037, except federal NOLs from 2018 to 2020 which will never expire. The Company also had federal research and development tax credit carryforwards of approximately $8.7 million, which will begin expiring in 2020, and California research and development credits of approximately $8.4 million, which do not have an expiration date.

A reconciliation of income taxes provided at the federal statutory rate (21%) to the actual income tax provision is as follows (in thousands):

	Year Ended
	December 31,
	2020			2019
Income tax benefit computed at U.S. statutory rate	$	(794	)	$	(542	)
Research and development credits		(66	)		(170	)
Amortization of intangible assets		(60	)		(60	)
Goodwill impairment		—			17
Valuation allowance changes affecting tax provision		919			752
Other		1			3
Income tax provision	$	—		$	—

The losses before income tax provision for the years ended December 31, 2020 and 2019 were solely attributable to US operations.