Please see this answer from DeanM15
The Alternative Minimum Tax is a separate taxation system that runs in parallel to the regular taxation system. The software runs both systems and will choose the system that taxes you the most (as the IRS requires it to do).
If you are subject to the AMT, you will see Form 6251, Alternative Minimum Tax—Individuals, in your return and an amount on Line 1, Schedule 2 of your 2019 Form 1040 which represents the difference between the two taxing systems.
In general, the AMT expands the amount of income that is taxed by adding items that are tax-free in the regular tax system. It also disallows many deductions under the regular tax system. It then applies a lower rate to the expanded taxable income. You can find out more about the AMT here.
