(8) Stock‑Based Compensation

The Company has two equity incentive plans: the 2012 Stock Incentive Plan and the Amended and Restated 2019 Equity Incentive Plan. New awards can only be granted under the Amended and Restated 2019 Equity Incentive Plan (the “Plan”). At December 31, 2020, 1,199,997 shares were available for future issuances. The Plan is subject to an annual increase, subject to prior approval by the Company’s board of directors, equal to the lesser of (i) 432,442 shares, (ii) 4% of the shares outstanding on the last day of the immediately preceding fiscal year and (iii) such smaller number of shares as determined by the board of directors. The Plan provides for the grant of incentive stock options, nonqualified stock options, restricted stock awards, restricted stock units and/or stock appreciation rights to employees, directors, and other persons, as determined by the Company’s board of directors. The Company’s stock options vest based on the terms in each award agreements and generally vest over four years and have a term of 10 years. The Company estimates forfeitures that it expects will occur and adjusts expense for actual forfeitures in the periods they occur.

The Company measures employee and nonemployee stock‑based awards at grant‑date fair value and records compensation expense ratably over the vesting period of the award. The Company recorded stock‑based compensation expense in the following expense categories of its accompanying consolidated statements of operations (in thousands):


	Year ended December 31,
	2020		2019		2018
Sales and marketing	$	696	$	164	$	68
General and administrative		1,030		225		115
Research and development		332		68		33
Total stock‑based compensation	$	2,058	$	457	$	216

The following table summarizes stock option activity for the Plan:


				Weighted
				average
		Weighted		remaining
	Number of	average exercise		contractual term
	shares	price per share		(years)
Outstanding at January 1, 2018	350,914	$	5.81
Granted	152,016		5.93
Exercised	(1,377)		5.57
Early exercised	(427)		5.93
Canceled/forfeited	(11,904)		5.93
Outstanding at December 31, 2018	489,222		5.84
Granted	978,415		12.51
Exercised	(2,527)		5.93
Early exercised	(471)		5.93
Canceled/forfeited	(43,697)		8.58
Outstanding at December 31, 2019	1,420,942		10.35
Granted	175,086		15.03
Exercised	(27,783)		6.29
Canceled/forfeited	(70,037)		12.41
Outstanding at December 31, 2020	1,498,208	$	10.87	7.95
Vested and expected to vest at December 31, 2020	1,439,422	$	10.80	7.91
Exercisable at December 31, 2020	647,987	$	8.40	6.80

The 2012 Stock Incentive Plan and the Amended and Restated 2019 Equity Incentive Plan provide the holders of stock options an election to early exercise prior to vesting. The Company had the right, but not the obligation, to repurchase early exercised options without transferring any appreciation to the employee if the employee terminates employment before the end of the original vesting period. The repurchase price is the lesser of the original exercise price or the then fair value of the common stock. At December 31, 2020, $1,000 of proceeds from early exercised options are recognized as a current liability in other current liabilities in the accompanying consolidated balance sheet.

The following table summarizes activity relating to early exercise of stock options:


		Number of
		shares
Unvested balance at January 1, 2018		1,034
Early exercised		427
Vested		(549)
Unvested balance at December 31, 2018		912
Early exercised		471
Vested		(628)
Unvested balance at December 31, 2019		755
Vested		(306)
Forfeited		(267)
Unvested balance at December 31, 2020		182

The weighted average grant‑date fair value per share of options granted was $8.13, $6.81 and $1.08 for the years ended December 31, 2020, 2019 and 2018, respectively. The aggregate intrinsic value of options exercised was $0.2 million for the year ended December 31, 2020 and nominal for the years ended December 31, 2019 and 2018, respectively. As of December 31, 2020, the total unrecognized compensation expense related to unvested employee and nonemployee stock option awards was $4.9 million, which is expected to be recognized in expense over a weighted‑average period of approximately 2.6 years.

Estimating Fair Value of Stock Options

The fair value of each grant of stock options was determined by the Company using the methods and assumptions discussed below. Certain of these inputs are subjective and generally require judgment to determine.

Expected term – The expected term of stock options represents the weighted average period the stock options are expected to be outstanding. The Company uses the simplified method for estimating the expected term as provided by the Securities and Exchange Commission. The simplified method calculates the expected term as the average time to vesting and the contractual life of the options.

Expected volatility – Due to the Company’s limited operating history and lack of adequate company‑specific historical or implied volatility, the expected volatility assumption was determined by examining the historical volatilities of a group of industry peers whose share prices are publicly available.

Risk‑free interest rate – The risk‑free rate assumption is based on the U.S. Treasury instruments, the terms of which were consistent with the expected term of the Company’s stock options.

Expected dividend – The Company has not paid and does not intend to pay dividends.

The fair value of each option was estimated on the date of grant using the weighted average assumptions in the table below:


	Year ended December 31,
	2020		2019		2018
Expected dividend yield	—		—		—
Expected volatility	59.1	%	55.9	%	56.5	%
Risk‑free interest rate	0.87	%	1.82	%	2.77	%
Expected term (in years)	5.98		6.24		6.25