In July 2018, the Company adopted the 2018 Incentive Award Plan (the “2018 Plan”). Under the 2018 Plan, which expires in July 2028, the Company may grant equity-based awards to individuals who are employees, officers, directors or consultants of the Company. Options issued under the 2018 Plan, will generally expire ten years from the date of grant and vest over a four-year period. As of June 30, 2020, 2,485,843 shares were available for future issuance under the 2018 Plan.

The 2018 Plan contains a provision that allows annual increases in the number of shares available for issuance on the first day of each calendar year through January 1, 2028 in an amount equal to the lesser of: (i) 5% of the aggregate number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding calendar year, or (ii) such lesser amount determined by the Company. Under this evergreen provision, on January 1, 2020, an additional 1,214,804 shares became available for future issuance under the 2018 Plan.

In February 2015, the Company adopted the Crinetics Pharmaceuticals, Inc. 2015 Stock Incentive Plan (the “2015 Plan”), which provided for the issuance of equity awards to the Company’s employees, members of its board of directors and consultants. In general, options issued under this plan vest over four years and expire after 10 years. Subsequent to the adoption of the 2018 Plan, no additional equity awards can be made under the 2015 Plan.

Certain awards under the 2015 Plan allowed for exercise prior to vesting. Shares issued under such early-exercise provisions are subject to repurchase by the Company until they become fully vested. As of June 30, 2020, 23,311 unvested shares issued under early-exercise provisions were subject to repurchase by the Company. The condensed consolidated balance sheet reflects an unvested stock liability of $34,000 as of June 30, 2020.

In July 2018, the Company adopted the 2018 Employee Stock Purchase Plan (the “ESPP”). The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation. As of June 30, 2020, an aggregate of 638,720 shares of common stock were available for issuance under the ESPP.

The ESPP contains a provision that allows annual increases in the number of shares available for issuance on the first day of each calendar year through January 1, 2028 in an amount equal to the lesser of: (i) 1% of the aggregate number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding calendar year, or (ii) such lesser amount determined by the Company. Under this evergreen provision, on January 1, 2020, an additional 242,961 shares became available for future issuance under the ESPP.

Activity under the Company’s stock option plans during the six months ended June 30, 2020 was as follows:

				Weighted-		Weighted-		Aggregate
	Options			Average		Average		Intrinsic
	Outstanding			Exercise		Remaining		Value
	(000’s)			Price		Term		(000’s)
Balance at December 31, 2019		3,127		$	11.52
Granted		1,019		$	21.58
Exercised		(84	)	$	1.52
Forfeited and expired		(73	)	$	20.81
Balance at June 30, 2020		3,989		$	14.13		8.4	$	24,208
Exercisable at June 30, 2020		1,628		$	9.55		7.7	$	15,549

Aggregate intrinsic value is calculated as the difference at June 30, 2020 between the closing price of the Company’s common stock and the exercise price of stock options that had exercise prices below the closing price.

The aggregate intrinsic value of options exercised during the six months ended June 30, 2020 was $1.5 million.

The Company utilizes the Black-Scholes option pricing model to value awards under its equity plans. The following table summarizes the weighted average assumptions used to estimate the fair value of stock options granted under the Company’s stock option plans and the shares purchasable under the ESPP during the periods presented:

Stock Option Plans	2020	2019
Expected option term	6.0 years	5.9 years
Expected volatility	77%	78%
Risk free interest rate	1.1%	2.4%
Expected dividend yield	—%	—%

ESPP	2020	2019
Expected option term	2.0 years	1.3 years
Expected volatility	82%	62%
Risk free interest rate	0.0%	2.3%
Expected dividend yield	—%	—%

The key assumptions used in determining the fair value of equity awards, and the Company’s rationale, were as follows: (i) Expected option term - the expected term represents the period that options are expected to be outstanding and has been estimated using the simplified method, which is an average of the contractual option term and its vesting period; (ii) Expected volatility - the expected volatility assumption is based on volatilities of a peer group of similar companies in the biotechnology industry whose share prices are publicly available; (iii) Risk-free interest rate - the risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero coupon U.S. Treasury notes with maturities that approximate the expected terms of awards; and (iv) Expected dividend yield - the expected dividend yield assumption is zero as the Company has never paid dividends and has no present intention to do so in the future.

The weighted-average fair value of stock options awarded during the six months ended June 30, 2020 and 2019 was $14.37 and $16.95 per share, respectively.

Stock-based compensation expense for the equity awards issued by the Company to employees and non-employees for the periods presented below was as follows (in thousands):

	Three months ended June 30,				Six months ended June 30,
	2020		2019		2020		2019
Included in research and development	$	1,227	$	839	$	2,313	$	1,378
Included in general and administrative		1,301		742		2,362		1,231
Total stock-based compensation expense	$	2,528	$	1,581	$	4,675	$	2,609

As of June 30, 2020, unrecognized stock-based compensation cost related to option awards and to the ESPP was $26.9 million and $0.9 million, respectively, which is expected to be recognized over a remaining weighted-average period of approximately 2.9 years and 1.6 years, respectively.