Our share-based compensation consists of performance-based stock options, term-based stock options, restricted stock units (“RSUs”), and performance-based stock units (“PSUs”). We also offer an employee stock purchase plan.

Prior to November 1, 2013, Ceridian employees participated in a share-based compensation plan of the former ultimate parent of Ceridian, the 2007 Stock Incentive Plan (“2007 SIP”). Effective November 1, 2013, although most participants who held stock options under the 2007 SIP converted their options to a newly created option plan, the 2013 Ceridian HCM Holding Inc. Stock Incentive Plan, as amended (“2013 SIP”), a small number of participants maintained their stock options in the 2007 SIP. Concurrent with the IPO and legal reorganization, all outstanding stock options under the 2007 SIP were converted into options to purchase common stock of Ceridian. As of December 31, 2020, there were 2,500 stock options outstanding under the 2007 SIP.

Stock options awarded under the 2013 SIP vest either annually on a pro rata basis over a four- or five-year period or on a specific date if certain performance criteria are satisfied and certain equity values are attained. In addition, upon termination of service, all vested options must be exercised generally within 90 days after termination, or these awards will be forfeited. The stock option awards have a 10-year contractual term and have an exercise price that is not less than the fair market value of the underlying stock on the date of grant. As of December 31, 2020, there were 2,219,243 stock options and RSUs outstanding under the 2013 SIP. We do not intend to grant any additional awards under the 2007 SIP or the 2013 SIP.

As part of the 2013 SIP, the Board of Directors approved a stock appreciation rights program that authorized the issuance of up to 600,000 stock appreciation rights. The performance criteria for all stock appreciation rights was met on April 30, 2018, resulting in the vesting and cash settlement of all outstanding stock appreciation rights. We recognized $1.5 million of share-based compensation expense related to the vesting of these stock appreciation rights during the year ended December 31, 2018. As of December 31, 2020 and 2019, there were no remaining outstanding stock appreciation rights.

On April 24, 2018, in connection with the IPO, the Board of Directors approved the Ceridian HCM Holding Inc. 2018 Equity Incentive Plan (“2018 EIP”), which authorized the issuance of up to 13,500,000 shares of common stock to eligible participants through equity awards (the “Share Reserve”). The Share Reserve may be increased on March 31 of each of the first ten calendar years during the term of the 2018 EIP, by the lesser of (i) three percent of the number of shares of our common stock outstanding on each January 31 immediately prior to the date of increase or (ii) such number of shares of our common stock determined by the Board of Directors. As of March 31, 2020, the Share Reserve was increased by 4,199,089 shares, pursuant to the terms of the 2018 EIP.

Equity awards under the 2018 EIP vest either annually or quarterly on a pro rata basis, generally over a one-, three-, or four-year period. In addition, upon termination of service, all vested awards must be exercised within 90 days after termination, or these awards will be forfeited. The equity awards have a 10-year contractual term and awards with an exercise price have such that is not less than the fair market value of the underlying stock on the date of the grant. As of December 31, 2020, there were 12,130,215 stock options, RSUs, and PSUs outstanding and 9,765,067 shares available for future grants of equity awards under the 2018 EIP.

Share-based compensation expense was $65.8 million, $36.5 million, and $24.7 million for the years ended December 31, 2020, 2019, and 2018, respectively.

Performance-based option activity under the 2007 SIP, the 2013 SIP, and the 2018 EIP was as follows:

	Shares			Weighted Average Exercise Price (per share)			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Performance-based options outstanding at December 31, 2017		1,038,147		$	13.46			3.5	$	—
Granted		—			—			—		—
Exercised		(663,412	)		(13.46	)		—		—
Forfeited or expired		(8,358	)		(13.46	)		—		—
Performance-based options outstanding at December 31, 2018		366,377		$	13.50			3.1	$	7.7
Granted		—			—			—		—
Exercised		(298,096	)		(13.48	)		—		—
Forfeited or expired		—			—			—		—
Performance-based options outstanding at December 31, 2019		68,281		$	13.58			2.6	$	3.7
Granted		1,818,728			65.27			—		—
Exercised		(42,730	)		(13.46	)		—		—
Forfeited or expired		—			—			—		—
Performance-based options outstanding at December 31, 2020		1,844,279		$	64.55			9.2	$	77.5
Performance-based options exercisable at December 31, 2020		25,551		$	13.78			1.7	$	2.4

The performance criteria for all outstanding performance-based stock options granted prior to 2018 was met on June 7, 2018, resulting in vesting on this date. We recognized $4.8 million of share-based compensation expense related to the vesting of these performance-based stock options during the year ended December 31, 2018.

In 2020, 1,500,000 performance-based stock options (“the Performance Option Award”) were granted under the 2018 EIP with an exercise price of $65.26. The vesting conditions for the Performance Option Award are based on the Company’s performance on the New York Stock Exchange (“NYSE”) with 750,000 shares available to vest when the Company’s per share closing price on the NYSE meets or exceeds $110.94, or 1.7 times the exercise price, for ten consecutive trading days, and the remaining 750,000 shares are available to vest when the Company’s per share closing price on the NYSE meets or exceeds $130.52, or 2.0 times the exercise price, for ten consecutive trading days. The Performance Option Award has a minimum time-based vesting period of 3 years. The vesting conditions must be achieved prior to May 8, 2025, or any unvested portion of the Performance Option Award will terminate. A Monte Carlo simulation model was used to determine the fair value of these performance-based stock options. The Monte Carlo model utilizes multiple input variables that determine the probability of satisfying the market conditions stipulated in the award. We have estimated an expected term of 5.3 years, based on the vesting period and contractual term.

The remaining performance-based stock options granted during the twelve months ended December 31, 2020, under the 2018 EIP primarily include vesting conditions based on migrations of customers to Dayforce. There are two tranches of stock options, in which the vesting conditions must be met either prior to September 13, 2021, or September 13, 2022.

As of December 31, 2020, there was $24.3 million of share-based compensation expense related to unvested performance-based stock option awards not yet recognized, which is expected to be recognized over a weighted average period of 3.2 years.

Term-based stock option activity under the 2007 SIP, the 2013 SIP, and the 2018 EIP, was as follows:

	Shares			Weighted Average Exercise Price (per share)			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in millions)
Term-based options outstanding at December 31, 2017		10,994,181		$	16.52			6.9	$	48.8
Granted		5,236,037			23.07			—		—
Exercised		(2,501,983	)		(15.26	)		—		—
Forfeited or expired		(178,466	)		(17.30	)		—		—
Term-based options outstanding at December 31, 2018		13,549,769		$	19.28			7.5	$	206.8
Granted		4,297,472			49.74			—		—
Exercised		(4,358,867	)		(17.37	)		—		—
Forfeited or expired		(343,437	)		(24.14	)		—		—
Term-based options outstanding at December 31, 2019		13,144,937		$	29.74			7.8	$	501.3
Granted		2,282,334			66.06			—		—
Exercised		(3,889,096	)		(20.42	)		—		—
Forfeited or expired		(555,101	)		(32.09	)		—		—
Term-based options outstanding at December 31, 2020		10,983,074		$	40.47			7.8	$	725.9
Term-based options exercisable at December 31, 2020		3,085,305		$	28.50			6.8	$	240.9

The fair value of the term-based stock options was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

For stock options granted under the 2013 SIP and 2018 EIP, we estimated an expected term of 7.0 years, based on the vesting period and contractual life. As of December 31, 2020, there was $85.4 million of share-based compensation expense related to unvested term-based awards not yet recognized, which is expected to be recognized over a weighted average period of 1.7 years. As of December 31, 2020, there were 3,085,305 vested term-based stock options.

	Shares
RSUs outstanding at December 31, 2017		605,990
Granted		164,073
Shares issued upon vesting of RSUs		(105,990	)
Forfeited or canceled		—
RSUs outstanding at December 31, 2018		664,073
Granted		193,033
Shares issued upon vesting of RSUs		(17,288	)
Forfeited or canceled		(20,000	)
RSUs outstanding at December 31, 2019		819,818
Granted		685,997
Shares issued upon vesting of RSUs		(73,475	)
Forfeited or canceled		(42,955	)
RSUs outstanding at December 31, 2020		1,389,385
RSUs releasable at December 31, 2020		423,479

During the year ended December 31, 2020, 226,616 RSUs vested, of which 73,475 shares of common stock were issued. As of December 31, 2020, there were 423,479 RSUs vested and releasable. RSUs generally vest annually over a one-, three-, or four-year period. As of December 31, 2020, there was $44.2 million of share-based compensation expense related to unvested RSUs not yet recognized, which is expected to be recognized over a weighted average period of 1.5 years.

In 2020, 145,017 PSUs were granted under the 2018 EIP and 9,797 PSUs were forfeited and cancelled. The vesting conditions for the PSUs were based on the Company’s performance against Cloud revenue and adjusted EBITDA margin goals under Ceridian HCM Holding Inc. 2020 Management Incentive Plan (the “2020 MIP”) for the incentive period of January 1, 2020 through December 31, 2020. The vesting conditions for the PSUs were not met for the incentive period and as a result, the PSUs did not vest and no share-based compensation expense was recognized for these awards during the year ended December 31, 2020.

On November 9, 2018, the Compensation Committee of the Board of Directors approved the Ceridian HCM Holding Inc. Global Employee Stock Purchase Plan (the “GESPP”), which authorizes the issuance of up to 2,500,000 shares of common stock to eligible participants through purchases via payroll deductions. The purchase price is the lower of (i) 85% of the fair market value of a share of common stock on the offering date (the first trading day of the offering period commencing on January 1 and concluding on December 31) or (ii) 85% of the fair market value of a share of common stock on the purchase date. The GESPP shall continue for ten years, unless terminated sooner as provided under the GESPP. In 2020, quarterly purchase periods commenced on January 1, April 1, July 1, and October 1. Shares were purchased on the last trading day of the respective purchase periods. During 2020, shares were purchased on March 31, June 30, September 30, and December 31.

The fair value of the stock purchase rights granted under the GESPP was estimated using the following weighted-average assumptions: