Tax reform eliminated the corporate AMT. So, tax returns for 2017 will be the last ones to use it.
A variety of exclusions, deductions, and credits are available to corporations, which often allow them to reduce the amount of tax that they are required to pay on the income they earn, sometimes to zero. To ensure that these corporations pay at least some tax on their income, Sec. 55 imposes an alternative minimum tax (AMT), which requires many corporations to add back some of these deductions and credits and pay tax on this reconfigured amount.
The calculation of a corporation’s AMT is parallel to its regular tax calculation. A corporation must calculate tax under both systems and determine its tentative minimum tax. Then the tentative minimum tax and the regular tax are compared. If the corporation’s tentative minimum tax amount exceeds its regular tax amount, the excess is the corporation’s alternative minimum tax, which it pays in addition to its regular tax.