Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Taxes

Schedule of reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax

	Year ended
	December 31,
	2019		2018
Federal statutory income tax rate	(21.0)	%	(21.0)	%
State taxes, net of federal benefit	(6.2)		(4.8)
Federal and state research and development tax credits	(6.0)		(2.9)
Stock‑based compensation expense	0.7		4.5
Other	0.5		0.5
Increase in deferred tax asset valuation allowance	32.0		23.7
Effective income tax rate	—	%	—	%

Summary of changes in the valuation allowance for deferred tax assets

	December 31,
	2019		2018
Deferred tax assets:
Net operating loss carryforwards	$	61,160	$	25,508
Research and development tax credit carryforwards		13,525		3,824
Accrued expenses		1,142		1,139
Capitalized intellectual property costs		1,073		764
Capitalized research and development expense		109		120
Operating lease liabilities		12,952		—
Stock‑based compensation expense		9,156		2,652
Total deferred tax assets		99,117		34,007
Deferred tax liabilities:
Operating lease assets		(12,720)		—
Depreciation and other		(513)		(341)
Total deferred tax liabilities		(13,233)		(341)
Valuation allowance		(85,884)		(33,666)
Net deferred tax assets	$	—	$	—

Net deferred tax assets

	Year ended
	December 31,
	2019		2018
Valuation allowance as of beginning of year	$	33,666	$	12,575
Decreases recorded as benefit to income tax provision		—		—
Increases recorded to income tax provision		52,218		21,091
Valuation allowance as of end of year	$	85,884	$	33,666