As of March 31, 2021, there were 1,980,405 shares and 2,329,534 shares available for grant under The Hanover Insurance Group 2014 Long-Term Incentive Plan and The Hanover Insurance Group 2014 Employee Stock Purchase Plan, respectively.

Compensation cost for the Company’s stock-based awards and the related tax benefits were as follows:

Information on the Company’s stock option activity for the three months ended March 31, 2021 and 2020 is summarized below.

	Three Months Ended March 31,
	2021					2020
(in whole shares and dollars)	Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price
Outstanding, beginning of period		1,282,278		$	93.64		1,121,559		$	87.88
Granted		178,040			115.35		240,705			118.54
Exercised		(67,954	)		80.96		(35,918	)		79.40
Forfeited or cancelled		—			—		—			—
Outstanding, end of period		1,392,364			97.03		1,326,346			93.67

The Company currently issues time-based, market-based and performance-based restricted stock units to eligible employees, all of which generally vest after 3 years of continued employment.

The following tables summarize activity information about employee restricted stock units:

	Three Months Ended March 31,
	2021					2020
(in whole shares and dollars)	Shares			Weighted Average Grant Date Fair Value		Shares			Weighted Average Grant Date Fair Value
Time-based restricted stock units:
Outstanding, beginning of period		350,480		$	116.37		335,166		$	109.55
Granted		168,092			115.04		136,634			118.60
Vested		(109,667	)		110.68		(78,773	)		85.44
Forfeited		(7,388	)		116.82		(2,861	)		112.24
Outstanding, end of period		401,517			117.37		390,166			117.56
Performance-based and market-based restricted stock units:
Outstanding, beginning of period		97,043		$	119.59		86,252		$	110.70
Granted		62,143			114.66		54,415			105.10
Vested		(43,506	)		122.27		(36,499	)		80.26
Forfeited		—			—		—			—
Outstanding, end of period		115,680			115.93		104,168			118.45

In the first three months of 2021 and 2020, the Company granted market-based awards totaling 37,348 and 34,911, respectively, to certain members of senior management, which are included in the table above as performance and market-based restricted stock activity. The vesting of these stock units is based on the relative total shareholder return (“TSR”) of the Company. This metric is generally based on relative TSR for a three-year period as compared to a pre-selected group of property and casualty companies. The fair value of market-based awards was estimated at the date of grant using a valuation model. These units have the potential to range from 0% to 150% of the shares disclosed. Included in the amount granted above in 2021 and 2020 are 14,501 shares and 13,532 shares, respectively, related to market-based awards that achieved a payout in excess of 100%. These awards vested in the first quarters of 2021 and 2020, respectively.

The Company also granted performance-based restricted stock units in 2021 and 2020, totaling 21,401 and 19,504, respectively, which are based upon the Company’s achievement of return on equity objectives. These units have the potential to range from 0% to 150% of the shares disclosed, which varies based on grant year and individual participation level. Increases above the 100% target level are reflected as granted in the period in which performance-based stock unit goals are achieved. Decreases below the 100% target level are reflected as forfeited. There were no performance-based awards that vested in 2021 or 2020.