Yes, the AMT will prevent (or limit) you property tax deduction from having any effect on your tax return. I am confident TurboTax is calculating your tax correctly. There are lots of moving parts in a tax return. When you get to the point where you are paying AMT, you may also be subject to the phase out of exemptions and itemized deductions and subject to the net investment tax, etc. And if you have any capital gains or qualified dividends, those are taxed at at different rate. TurboTax does have an accuracy guarantee, so if your tax is calculated incorrectly, TurboTax will reimburse you for any penalty and interest you have to pay as a result (they don't pay the tax).
