Stock-Based Compensation (Tables)

A summary of all of our non-qualified stock option activity for the Equity Plans for the six months ended June 30, 2017, is as follows:



	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Term (in years)	Aggregate Intrinsic Value (in millions)
Outstanding — December 31, 2016	2,697,136	$	13.59	3.0	$	2
Granted	1,476,480	$	11.70
Forfeited	15,721	$	11.69
Expired	22,800	$	17.69
Outstanding — June 30, 2017	4,135,095	$	12.90	5.0	$	6
Exercisable — June 30, 2017	2,674,336	$	13.55	2.5	$	4
Vested and expected to vest – June 30, 2017	3,946,197	$	12.96	4.8	$	6

Certain assumptions were used in order to estimate fair value for options as noted in the following table:



	2017
Expected term (in years)⁽¹⁾	7.3 - 10.0
Risk-free interest rate⁽²⁾	2.25		%
Expected volatility⁽³⁾	33 - 40		%
Dividend yield⁽⁴⁾	—
Weighted average grant-date fair value (per option)	$	5.38

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(1)	Expected term calculated using historical exercise data.


(2)	Zero Coupon U.S. Treasury rate or equivalent based on expected term.


(3)	Volatility calculated using the implied volatility of our exchange traded stock options.


(4)	We have never paid cash dividends on our common stock and we do not anticipate any cash dividend payments on our common stock in the near future.

A summary of our restricted stock and restricted stock unit activity for the Calpine Equity Incentive Plans for the six months ended June 30, 2017, is as follows:



	Number of Restricted Stock Awards		Weighted Average Grant-Date Fair Value
Nonvested — December 31, 2016	4,869,648		$	15.83
Granted	3,606,816		$	11.76
Forfeited	493,472		$	13.98
Vested	1,650,036		$	17.11
Nonvested — June 30, 2017	6,332,956	⁽¹⁾	$	13.32

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(1)	Includes 63,075 shares of restricted stock and restricted stock units outstanding under the Director Plans and 6,269,881 shares of restricted stock and restricted stock units outstanding under the Equity Plans

A summary of our performance share unit activity for the six months ended June 30, 2017, is as follows:



	Number of Performance Share Units	Weighted Average Grant-Date Fair Value
Nonvested — December 31, 2016	890,587	$	17.90
Granted	478,984	$	10.73
Forfeited	54,638	$	18.38
Vested⁽¹⁾	30,312	$	17.21
Nonvested — June 30, 2017	1,284,621	$	15.22

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(1)	In accordance with the applicable performance share unit agreements, performance share units granted to employees who meet the retirement eligibility requirements stipulated in the Equity Plans are fully vested upon the later of the date on which the employee becomes eligible to retire or one-year anniversary of the grant date.