What is the alternative minimum tax (AMT)?

How the AMT works is that it builds up in parallel to your regular tax liability, according to a different ruleset. In the end, you pay either the AMT or your regular tax bill — whichever is highest. 

Every year that you file a tax return, you’re required to calculate your regular tax liability as well as your AMT. This is an involved calculation, so it is usually done by the software or accountant that you use to file your taxes.