8. Stock Option Plans

In February 2014, the Company adopted the 2014 Equity Incentive Plan (the “2014 Plan”), which was subsequently amended in November 2014, July 2015 and September 2015, under which it granted incentive stock options (“ISOs”) or non-qualified stock options (“NSOs”). Terms of stock agreements, including vesting requirements, are determined by the board of directors or a committee authorized by the board of directors, subject to the provisions of the 2014 Plan. In general, awards granted by the Company vest over four years and have maximum exercise term of 10 years. The 2014 Plan provides that grants must be at an exercise price of 100% of fair market value of the Company’s common stock as determined by the board of directors on the date of the grant.

In connection with the consummation of the IPO in March 2016, the 2016 Equity Incentive Award Plan (the “2016 Plan”), became effective. Under the 2016 Plan, incentive stock options, non-statutory stock options, stock purchase rights and other stock-based awards may be granted. Terms of stock agreements, including vesting requirements, are determined by the board of directors or a committee authorized by the board of directors, subject to the provisions of the 2016 Plan. In general, awards granted by the Company vest over four years and have maximum exercise term of 10 years. The 2016 Plan provides that grants must be at an exercise price of 100% of fair market value of the Company’s common stock as determined by the board of directors on the date of the grant. In conjunction with adopting the 2016 Plan, the 2014 Plan was terminated and no further awards will be granted under the 2014 Plan. Options outstanding under the 2014 Plan as of the effective date of the 2016 Plan that are forfeited or lapse unexercised may be re-issued under the 2016 Plan, up to a maximum of 1,136,229 shares.

Activity under the Company’s stock option plans is set forth below:


		Options Outstanding
			Weighted ‑
	Shares		Average
	Available	Number of	Exercise
	for Grant	Options	Price
Balance at December 31, 2018	2,486,637	3,778,259	$	10.32
Additional shares authorized	1,170,000	—		—
Options granted	(2,029,000)	2,029,000		3.61
Options exercised	—	(87,303)		0.28
Options forfeited	76,546	(76,546)		11.67
Balance at December 31, 2019	1,704,183	5,643,410	$	8.05

The following table summarizes information about stock options outstanding at December 31, 2019 and 2018:


			Options Outstanding				Options Vested
			at December 31, 2019				at December 31, 2019
				Weighted				Weighted
				Average				Average	Weighted
				Remaining	Weighted			Remaining	Average
				Contractual	Average			Contractual	Exercise
Exercise Price			Number	Life (in Years)	Exercise Price		Number	Life (in Years)	Price
$0.28	-	$2.56	191,000	5.66	$	0.36	184,730	5.52	$	0.29
$3.01	-	$4.65	2,027,500	9.75	$	3.61	32,375	6.01	$	4.64
$4.84		$7.59	1,061,522	8.94	$	5.95	261,504	8.90	$	5.98
$9.52	-	$14.43	1,051,738	7.98	$	10.83	593,596	7.93	$	10.90
$15.00	-	$16.70	1,311,650	6.51	$	15.49	1,138,764	6.44	$	15.40
			5,643,410	8.38	$	8.05	2,210,969	7.05	$	11.66


			Options Outstanding				Options Vested
			at December 31, 2018				at December 31, 2018
				Weighted				Weighted
				Average				Average	Weighted
				Remaining	Weighted			Remaining	Average
				Contractual	Average			Contractual	Exercise
Exercise Price			Number	Life (in Years)	Exercise Price		Number	Life (in Years)	Price
$0.28	-	$4.65	301,803	6.44	$	0.72	261,373	6.42	$	0.68
$5.94	-	$9.52	1,101,750	9.92	$	6.10	3,585	8.69	$	8.92
$9.60	-	$14.43	1,026,180	8.97	$	10.89	269,731	8.70	$	10.56
$15.00	-	$16.70	1,348,526	7.50	$	15.49	834,456	7.38	$	15.37
			3,778,259	8.52	$	10.32	1,369,145	7.46	$	11.60

The weighted average grant date fair value of options granted for the years ended December 31, 2019, 2018 and 2017, was $2.53, $5.23 and $8.93, respectively.

Options outstanding and exercisable that had vested or were expected to vest at December 31, 2019 were as follows:


				Weighted
				Average	Aggregate
		Weighted		Remaining	Intrinsic
	Number	Average		Contractual	Value
	of shares	Exercise Price		Life (years)	(in thousands)
Vested	2,210,969	$	11.66	7.05	$	977,587
Expected to vest	3,432,441	$	5.72	9.24	$	3,713,778

In the table above, aggregate intrinsic value represents the difference between the exercise price of the options to purchase common stock and the estimated fair value of the Company’s common stock of $5.44.

The aggregate intrinsic value of stock options exercised in the years ended December 31, 2019, 2018 and 2017, was $0.4 million, $1.1 million and $0.3 million, respectively.

The total fair value of options that vested in the year ended December 31, 2019, 2018 and 2017, was $7.8 million, $7.1 million, and $5.8 million, respectively.