The Company maintains stock option programs for key employees, executives and directors. The plans, all of which have been approved by shareholder vote, provide for the granting of both nonqualified and incentive options. Options granted under the plans typically have a six-year term and vest over a four to five-year period. The fair value of shares vested for the six months ended June 30, 2019 and 2018 aggregated $0.07 million and $0.04 million, respectively. Compensation cost is recognized on a straight-line basis over the requisite service period for the entire award. It is generally our policy to issue new shares upon exercise of stock options.

Share based payment expense decreased income before income taxes by $0.95 million and $1.90 million for the three and six months ended June 30, 2019, respectively, as compared to $0.57 million and $1.08 million for the corresponding periods of the prior year. Share based payment expense decreased income attributable to Inter Parfums, Inc. by $0.56 million and $1.14 million for the three and six months ended June 30, 2019, respectively, as compared to $0.36 million and $0.68 million for the corresponding periods of the prior year.

As of June 30, 2019, the weighted average remaining contractual life of options outstanding is 3.61 years (2.08 years for options exercisable), the aggregate intrinsic value of options outstanding and options exercisable is $17.0 million and $8.1 million, respectively, and unrecognized compensation cost related to stock options outstanding aggregated $4.2 million.

Cash proceeds, tax benefits and intrinsic value related to stock options exercised during the six months ended June 30, 2019 and June 30, 2018 were as follows:

The weighted average fair values of the options granted by Inter Parfums, Inc. during the six months ended June 30, 2019 and 2018 were $14.83 and $10.73 per share, respectively, on the date of grant using the Black-Scholes option pricing model to calculate the fair value of options granted.

The assumptions used in the Black-Scholes pricing model for the periods ended June 30, 2019 and 2018 are set forth in the following table:

Expected volatility is estimated based on historic volatility of the Company’s common stock. The expected term of the option is estimated based on historic data. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of the grant of the option and the dividend yield reflects the assumption that the dividend payout as authorized by the Board of Directors would increase as the earnings of the Company and its stock price increases.

In September 2016, Interparfums SA, our 73% owned French subsidiary, approved a plan to grant an aggregate of 15,100 shares of its stock to employees with no performance condition requirement, and an aggregate of 133,000 shares to officers and managers, subject to certain corporate performance conditions. The shares, subject to adjustment for stock splits, will be distributed in September 2019 so long as the individual is employed by Interparfums SA at the time, and in the case of officers and managers, only to the extent that the performance conditions have been met. Once distributed, the shares will be unrestricted and the employees will be permitted to trade their shares.

The fair value of the grant of €16.87 per share (approximately $19.20 per share) has been determined based on the quoted share price of Interparfums SA shares as reported by the NYSE Euronext on the date of grant. The estimated number of shares to be distributed of 173,056 has been determined taking into account employee turnover and has been adjusted for stock splits. The aggregate cost of the grant of approximately $3.4 million is being recognized as compensation cost by Interparfums SA on a straight-line basis over the requisite three-year service period.

To avoid dilution of the Company’s ownership of Interparfums SA, all shares to be distributed pursuant to this plan will be pre-existing shares of Interparfums SA, purchased in the open market by Interparfums SA. In 2016 and 2018 , a total of 165,000 shares had been acquired at an aggregate cost of $3.7 million. During the six months ended June 30, 2019, an additional 8,056 shares were acquired at an aggregate cost of $0.3 million.

In December 2018, Interparfums SA approved an additional plan to grant an aggregate of 26,600 shares of its stock to employees with no performance condition requirement, and an aggregate of 133,000 shares to officers and managers, subject to certain corporate performance conditions. The shares, subject to adjustment for stock splits, will be distributed in June 2022 and will follow the same guidelines as the September 2016 plan.

The fair value of the grant of €27.45 per share (approximately $30.90 per share) has been determined based on the quoted stock price of Interparfums SA shares as reported by the NYSE Euronext on the date of grant. The estimated number of shares to be distributed of 148,864 has been determined taking into account employee turnover. The aggregate cost of the grant of approximately $4.9 million will be recognized as compensation cost by Interparfums SA on a straight-line basis over the requisite three and a half year service period.

Similar to the September 2016 plan, in order to avoid dilution of the Company’s ownership of Interparfums SA, all shares to be distributed pursuant to this plan will be pre-existing shares of Interparfums SA, purchased in the open market by Interparfums SA. During the six months ended June 30, 2019, the Company acquired 131,613 shares at an aggregate cost of $5.8 million.