11. Equity‑Based Compensation

General

The Company has granted options and restricted stock units to employees and non-employee directors to purchase the Company’s common stock under various stock incentive plans. The plans administered by a committee of the Board of Directors, which determines the terms of the awards granted. The committee may grant various forms of equity-based incentive compensation, including stock options, stock appreciation rights, restricted stock, restricted stock units and performance awards, among others. Stock options are granted with an exercise price equal to the closing market value of GMS common stock on the date of grant, have a term of ten years, and vest over terms of three to four years from the date of grant. Restricted stock units are granted with various vesting terms that range from one to three years from the date of grant. The Company’s current stock incentive plan provides for the issuance of a maximum of 2.5 million shares, of which approximately 1.8 million shares were still available for grant as of April 30, 2019. The Company intends to use authorized and unissued shares to satisfy share award exercises.

Share-based compensation expense related to stock options and restricted stock units was $3.6 million, $1.7 million and $2.4 million during the years ended April 30, 2019, 2018 and 2017, respectively, and is included in selling, general and administrative expenses in the Consolidated Statements of Operations and Comprehensive Income.

Stock Option Awards

The following table presents stock option activity as of and for the year ended April 30, 2019:


				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Options	Price		Life (years)	Value
	(shares and dollars in thousands)
Outstanding as of April 30, 2018	1,952	$	14.37	6.52	$	33,209
Options granted	374		25.58
Options exercised	(205)		12.36
Options forfeited	(41)		27.00
Options expired	—		—
Outstanding as of April 30, 2019	2,080	$	16.34	6.15	$	7,615
Exercisable as of April 30, 2019	1,644	$	13.66	5.41	$	7,615
Vested and expected to vest as of April 30, 2019	2,073	$	16.30	6.14	$	7,615

The aggregate intrinsic value represents the value of the Company’s closing stock price on the last trading day of the period in excess of the weighted average exercise price multiplied by the number of options outstanding, exercisable or expected to vest. Options expected to vest are unvested shares net of expected forfeitures. The total intrinsic value of options exercised during the years ended April 30, 2019, 2018 and 2017 was $1.6 million, $4.3 million and $0.6 million, respectively. As of April 30, 2019, there was $2.9 million of total unrecognized compensation cost related to stock options. That cost is expected to be recognized over a weighted-average period of 2.1 years.

The fair value of stock options granted during the years ended April 30, 2019, 2018 and 2017 was estimated using the Black-Scholes option-pricing model with the following assumptions:


	Year Ended April 30,
	2019		2018		2017
Volatility	33.71	%	30.86	%	40.68	%
Expected life (years)	6.0		6.0		6.0
Risk-free interest rate	2.87	%	2.18	%	1.55	%
Dividend yield	—	%	—	%	—	%

The weighted average grant date fair value of options granted during the years ended April 30, 2019, 2018 and 2017 was $9.72 per share, $12.81 per share and $9.68 per share, respectively. The expected volatility was based on historical volatility. The expected life of stock options was based on previous history of exercises. The risk‑free rate was based on the U.S. Treasury yield curve in effect at the time of grant for the expected term of the stock option. The expected dividend yield was 0% as we have not declared any common stock dividends to date and do not expect to declare common stock dividends in the near future. The fair value of the underlying common stock at the date of grant was determined based on the value of the Company’s closing stock price on the trading day immediately preceding the date of the grant.

Restricted Stock Units

The following table presents restricted stock unit activity for the year ended April 30, 2019:


		Weighted
	Number of	Average
	Restricted	Exercise
	Stock Units	Price
	(shares in thousands)
Outstanding as of April 30, 2018	22	$	37.49
Granted	193		24.66
Vested	(7)		37.49
Forfeited	(15)		26.41
Outstanding as of April 30, 2019	193	$	25.48

As of April 30, 2019, there was $3.3 million of total unrecognized compensation cost related to nonvested restricted stock units. That cost is expected to be recognized over a weighted-average period of 1.9 years.

Employee Stock Purchase Plan

During the year ended April 30, 2018, the Company established an employee stock purchase plan (“ESPP”), the terms of which allow for qualified employees (as defined) to participate in the purchase of shares of the Company’s common stock at a price equal to 90% of the lower of the closing price at the beginning or end of the last day of the purchase period, which is a six-month period ending on December 31 and June 30 of each year. The ESPP authorizes the issuance of a total 2.0 million shares, of which approximately 1.9 million shares were still available for issuance as of April 30, 2019. During the year ended April 30, 2019, 0.1 million shares of the Company’s common stock were purchased under the ESPP at an average price of $18.51 per share. The Company recognized $0.3 million and $0.1 million of stock-based compensation expense in during the years ended April 30, 2019 and 2018, respectively, related to the ESPP.