.47 , and $ 34.52 and $ 42.96 , respectively . the company calculates the value of each employee stock option , estimated on the date of grant , using the black-scholes option pricing model . the weighted-average estimated fair value of employee stock options granted during 2014 , 2013 and 2012 was $ 11.02 , $ 9.52 and $ 9.60 , respectively , using the following weighted-average assumptions: .