For example, if the strike price is $10 and you exercise 100 options, the exercise will cost $1,000 ($10 x 100) plus transaction fees and any withholding taxes due at exercise. Cashless exercise. You use your options to buy shares of stock, which you simultaneously sell in order to pay the exercise cost, transaction fees and any withholding taxes due at exercise. The tax catch is that when you exercise the options to purchase stock (but not before), you have taxable income equal to the difference between the stock price set by the option and the market price of the stock. In tax lingo, that's called the compensation element. When you exercise an incentive stock option there are a few different tax possibilities: You exercise the incentive stock options and sell the stock within the same calendar year: In this case, you pay tax on the difference between the market price at sale and the grant price at your ordinary income tax rate.