Upon the issuance of Host Inc.’s common stock for stock-based compensation, Host L.P. issues to Host Inc. common OP units of an equivalent value. Accordingly, these awards and related disclosures are included in both Host Inc.’s and Host L.P.’s consolidated financial statements.

Host Inc. maintains two stock-based compensation plans, the Comprehensive Stock and Cash Incentive Plan (the “2020 Comprehensive Plan”), under which Host Inc. may award to participating employees restricted stock units (“RSUs”), and the Employee Stock Purchase Plan. At December 31, 2020, there were approximately 15 million shares of Host Inc.’s common stock reserved and available for issuance under the 2020 Comprehensive Plan.

We recognize costs resulting from share-based payments in our financial statements over their vesting periods. No compensation cost is recognized for awards for which employees do not render the requisite services. We classify share-based payment awards granted in exchange for employee services as either equity-classified or liability-classified awards. Equity-classified awards are measured based on their fair value as of the date of grant. In contrast, liability-classified awards are re-measured to fair value each reporting period.

During 2020, 2019 and 2018, we recorded stock-based compensation expense of approximately $17 million, $15 million and $14 million, respectively. Shares granted in 2020, 2019 and 2018 totaled 2.2 million, 1.4 million and 1.2 million, respectively, while 1.2 million, 0.9 million and 0.8 million shares, respectively, vested during those years.

During 2020, Host Inc. granted 2.0 million RSU awards under the 2020 Comprehensive Plan, which amount represents the maximum number of RSUs that can be earned during the period of 2020 through 2022 if performance is at the “high” level of achievement and, for time based awards, the executive remains employed. The RSUs vest over a one, two or three-year period and 1.5 million RSUs were unvested at December 31, 2020. Total unrecognized compensation expense related to unvested RSU awards that vest through 2022 is approximately $11 million.

Vesting of RSUs awarded in 2020 is based on (1) continued employment on the vesting date (“Time-Based Award”); (2) the achievement of relative total shareholder return (“TSR”); and (3) our performance against certain annual strategic objectives. Approximately 40% of the RSUs are Time-Based Awards and vest on an annual basis over three years; approximately 30% of the RSUs are based on the satisfaction of the TSR compared to the NAREIT Equity Lodging & Resort index that serves as a relevant industry/asset specific measurement to our competitors and vest following a three year performance period; and the remaining 30% are based on our performance against certain strategic objectives and vest on an annual basis. The RSUs granted are considered equity-classified awards. As a result, the fair value of these awards is based on the fair value on the grant date, and such grant date fair value is not adjusted for subsequent movements thereof.

We value the time based awards using the closing stock price on the grant date multiplied by the percentage of shares expected to be released, which is 100% of the time based awards. We also value the strategic objective awards using the closing stock price on the grant date multiplied by the percentage of shares expected to be released; however, as a result of the strategic objective awards’ performance conditions, we reevaluate the percentage based on the probability of meeting the performance conditions each period. We value the TSR awards using the economic theory that is the basis for all valuation models, including Binominal, Black-Scholes, exotic options formulas, and Monte Carlo valuations, with the following assumptions:

In making these assumptions, we base the expected volatility on the historical volatility over three years using daily stock price observations. The beta is calculated by comparing the risk of our stock to the risk of the applicable peer group index, using three years of daily price data. We base the risk-free rate on the Treasury bond yields corresponding to the length of each performance period as reported by the Federal Reserve.

The payout schedule for the TSR awards is as follows, with linear interpolation for points between the 30^th and 75^th percentiles.

During 2020, 2019 and 2018, we recorded compensation expense of approximately $15 million, $13 million and $12 million, respectively, related to the RSU awards to senior executives. The following table is a summary of the status of our senior executive plans for the three years ended December 31, 2020:

	Year ended December 31,
	2020					2019					2018
	Shares			Fair Value		Shares			Fair Value		Shares			Fair Value
	(in millions)			(per share)		(in millions)			(per share)		(in millions)			(per share)
Balance, at beginning of year		1.2		$	13		0.9		$	14		0.7		$	14
Granted		2.0			10		1.3			14		1.1			16
Vested⁽¹⁾		(1.1	)		15		(0.7	)		19		(0.7	)		17
Forfeited/expired		(0.5	)		15		(0.3	)		19		(0.2	)		17
Balance, at end of year		1.6			10		1.2			13		0.9			14
Issued in calendar year ⁽¹⁾		0.4			19		0.4			17		0.3			20
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In addition to the share-based plans described above, we maintain an upper-middle management plan and an employee stock purchase plan. The upper-middle management awards are time-based, equity-classified awards that vest within three years of the grant date and compensation expense is recognized over the life of the award based on the grant date fair value. Through the employee stock purchase plan, employees can purchase stock at a discount of 10% of the lower of the beginning and ending stock price each quarter. During 2020, 2019 and 2018, we granted a total of 0.2 million shares, 0.1 million shares and 0.1 million shares, respectively, under these two programs and recorded compensation expense of approximately $2 million in each year.