I think I know what you're asking so I'll give it a go. When the stock option matures, the value of the stock provided through the options is included as income and is noted on your W-2 as income. The difference between that value and the value of the stock when you sell it has not been taxed until tax time. That difference is taxable and is what you should be paying taxes on. I forgot the name of the form that you'll get from Fidelity or whoever is managing your stock options plan but the last page should provide you with the fields to make this information clear. I hope that this helps.
