Fill out the Form 1040 worksheet to see if you it directs you to complete Form 6251 - Line 45 in the AMT section of the Form 1040 instructions. This will determine whether you are subject to AMT. The IRS also provides an AMT Assistant on their website to help identify the need for AMT.
Identify the method of depreciation used. If you are using the straight-line method of depreciation, none of your depreciation is subject to the AMT.
Recalculate depreciation for the tax year using the straight-line method. The straight-line method of depreciation spreads the cost of the asset, less the residual value of the asset, evenly across each period of the useful life of the asset.
Subtract the depreciation calculated using the straight-line method from the depreciation calculated using any other method. This is the amount of depreciation subject to the AMT.