Stock-Based Compensation | 7. Stock-Based Compensation Stock Option Valuation The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. Prior to the IPO, the Company was a private company and therefore lacked company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of its publicly-traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The relevant data used to determine the value of the stock option grants for the six months ended June 30, 2015 and 2014 are as follows: Six months ended June 30, 2015 2014 Risk-free interest rates 1.49-1.92 % 1.54-1.99 % Expected dividend yield 0.00 % 0.00 % Expected term (in years) 6.0 6.0 Expected volatility 76.4-81.4 % 61.9-66.9 % The following table summarizes stock option activity for the six months ended June 30, 2015: Shares Weighted Outstanding as of December 31, 2014 1,289,082 $ 10.26 Granted 555,750 22.81 Exercised (49,851 ) 4.30 Canceled (71,886 ) 16.19 Outstanding as of June 30, 2015 1,723,095 $ 14.23 Options vested and expected to vest at June 30, 2015 1,470,834 Options exercisable at June 30, 2015 616,940 The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. A total of 49,851 options were exercised during the six months ended June 30, 2015. The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2015 was $850,611. At June 30, 2015 and 2014 the Company had options for the purchase of 1,723,095 and 1,201,740 shares of common stock outstanding, respectively, with a weighted average remaining contractual term of 8.3, and 8.5 years, respectively, and with a weighted average exercise price of $14.23 and $9.86 per share, respectively. The weighted average grant date fair value of options granted during the six months ended June 30, 2015 and 2014 was $15.67 and $10.31, respectively. Stock-based Compensation The Company recorded stock-based compensation expense related to stock options for the three and six months ended June 30, 2015 and 2014 as follows: Three months ended June 30, Six months ended June 30, 2015 2014 2015 2014 Research and development $ 287,398 $ 182,279 $ 609,147 $ 295,797 General and administrative 682,461 475,529 1,368,962 798,507 $ 969,859 $ 657,808 $ 1,978,109 $ 1,094,304 As of June 30, 2015, unrecognized stock-based compensation expense for stock options outstanding was $13,912,389, which is expected to be recognized over a weighted average period of 2.9 years. As of June 30, 2014, unrecognized stock-based compensation expense for stock options outstanding was $7,673,376, which was expected to be recognized over a weighted average period of 2.9 years. |