You should be able to simply use the ISO "Guide me step by step" process here. You'll enter the full amount of the grant, you'll tell TurboTax how many shares you sold, TurboTax will calculate the AMT adjustment for the grant shares not sold.
Simply owing a ton of money to the IRS when you file your income tax return doesn't mean you're subject to a penalty. As long as the sum of your withholding and estimated taxes paid for the tax year gets you into one of the "safe harbors":
The lesser of
a)90% of the tax for the current year, or
b)100% of the tax shown on the return for the prior year. (If last year's return shows AGI over $150K (for married filing jointly) then change that "100%" figure to "110%.)
then you will not be assessed an underpayment penalty. If you think you won't get into any of the safe harbors then an earlier payment should be helpful either eliminating or at least minimizing any underpayment penalty.
Tom Young
