Click on Deductions & Credits, scroll down to the Estimates and Other Taxes Paid section, and click the Start button to the right of Credit for AMT Paid in Prior Year.
Please note that usually your prior year AMT is due to exclusion items and are not eligible for AMT credit. Please see below for items eligible for the AMT credit.
This credit, calculated on Form 8801: Credit for Prior Year Minimum Tax calculates how much of the AMT was related to deferral items, which generate credit for future years, as opposed to exclusion items which are not deductible for AMT, and consequently are lost.
Certain items in Lines 2-28 of the Form 6251 are simply not deductible for AMT purposes, such as taxes, home equity mortgage interest and miscellaneous deductions. Lines 2-5, 8-10, 13 and 14 are exclusion items. If you paid AMT based on entries on these lines, you will not receive a tax credit for AMT.
Other items create timing differences, such as depreciation differences between the two tax systems, and the phantom income from exercising incentive stock options. These items can generate a credit on Form 8801 and reduce your taxes in future years.
Lines 15-28 are deferral items. An AMT credit may be generated based on the reversal of the timing difference of these items. For example, AMT depreciation methods may be slower than those for the regular tax, but you will eventually receive the same deduction. To calculate and report your AMT credit you need to fill out Form 8801: Credit for Prior Year Minimum Tax.