The provision for income taxes differs from the amount expected by applying the federal statutory rate to the loss before taxes as follows:

	Year Ended December 31, 2018			Year Ended December 31, 2017			Year Ended December 31, 2016
Federal statutory income tax rate		21.00	%		34.00	%		34.00	%
Non-deductible expenses and other		(1.54	)%		(1.23	)%		(0.22	)%
Change in valuation allowance		(19.46	)%		(16.46	)%		(33.78	)%
Remeasurement of federal tax rate change		—			(16.32	)%		—
Total		0.00	%		0.00	%		0.00	%

As of December 31, 2018 and 2017, the components of the Company’s deferred tax assets are as follows (in thousands):

	Year Ended December 31, 2018			Year Ended December 31, 2017
Deferred tax assets:
Federal and state net operating loss carryforwards	$	16,076		$	11,101
Research and development credits carryforwards		5,087			2,706
Depreciation		3,942			3,489
Deferred Revenue		3,909			—
Other		1,724			1,292
Total deferred tax assets		30,738			18,588
Less valuation allowance		(30,738	)		(18,588	)
Net deferred tax assets	$	—		$	—

Deferred income taxes reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes, and (b) operating losses and tax credit carryforwards.

The Company’s accounting for deferred taxes involves the evaluation of a number of factors concerning the realizability of its net deferred tax assets. The Company primarily considered such factors as its history of operating losses, the nature of the Company’s deferred tax assets, and the timing, likelihood and amount, if any, of future taxable income during the periods in which those temporary differences and carryforwards become deductible. At present, the Company does not believe that it is more likely than not that the deferred tax assets will be realized; accordingly, a full valuation allowance has been established and no deferred tax asset is shown in the accompanying consolidated balance sheets. The valuation allowance increased by approximately $12.2 million, 10.2 million and $7.6 million, respectively, for the years ended December 31, 2018, 2017 and 2016.

In December 2017, the 2017 Tax Cuts and Jobs Act (2017 Tax Act) was enacted and includes a broad range of provisions, many of which differ significantly from those contained in previous U.S. tax law. Changes in tax law are accounted for in the period of enactment. As such, the Company’s consolidated financial statements as of December, 31, 2018 and 2017 reflect the impact of this 2017 Tax Act, which primarily consisted of measuring the Company’s deferred tax assets and valuation allowance using the newly enacted U.S. corporate tax rate.

At December 31, 2018, the Company has total net operating loss carryforwards (NOLs) of $70.9 million for federal income tax purposes, of which approximately $47.4 million begin to expire in 2035 and approximately $23.6 million that have no expiration date and federal research tax credits of approximately $3.6 million that begin to expire in 2035. The Company also has state NOLs of approximately $15.4 million that begin to expire in 2035, and state research tax credits of approximately $3.1 million that have no expiration date. Use of the NOLs and credit carryforwards may be subject to a substantial annual limitation due to the ownership change provisions of U.S. tax law, as defined in Section 382 and 383 of the Internal Revenue Code of 1986, as amended, and similar state provisions. The annual limitation may result in the expiration of NOLs and credits before use. The Company determined that an ownership change occurred in 2015 in conjunction with its Series A Preferred Stock financing and in 2017 in conjunction with its Series C Preferred Stock financing but does not expect that these ownership changes will result in the expiration of any the NOLs prior to utilization.

The Company has not been audited by the Internal Revenue Service, any state or foreign tax authority. The Company is subject to taxation in the United States and also beginning in 2017, in Australia. Because of the net operating loss and research credit carryforwards, all of the Company’s tax years, from 2015 to 2018, remain open to U.S. federal and California state tax examinations. In addition, the Company’s tax years from 2017 to 2018 are open to examination in Australia. There were no interest or penalties accrued at December 31, 2018, 2017 and 2016.

The Company follows the provisions of FASB Accounting Standards Codification (ASC 740-10), Accounting for Uncertainty in Income Taxes . ASC 740-10 prescribes a comprehensive model for the recognition, measurement, presentation and disclosure in financial statements of uncertain tax positions that have been taken or expected to be taken on a tax return. No liability related to uncertain tax positions is recorded in the consolidated financial statements. The Company’s reserve for unrecognized tax benefits is approximately $1.1 million and $0.6 million and $0.2 million at December 31, 2018, 2017 and 2016, respectively.

Due to the full valuation allowance at December 31, 2018, 2017 and 2016, current adjustments to the unrecognized tax benefit will have no impact on the Company’s effective income tax rate; any adjustments made after the valuation allowance is released will have an impact on the tax rate.

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):

	Year Ended December 31, 2018		Year Ended December 31, 2017		Year Ended December 31, 2016
Beginning balance	$	622	$	242	$	19
Additions for tax positions taken in a prior year		8		29		—
Additions for tax positions taken in current year		454		351		223
Ending balance	$	1,084	$	622	$	242

The Company does not anticipate material changes to its uncertain tax positions through the next 12 months.