The Alternative Minimum Tax, demystified

The Alternative Minimum Tax (AMT) is a parallel tax system designed to ensure high-income taxpayers pay at least some minimum tax, even after deductions and credits. Most taxpayers never encounter it. A specific group — people with large ISO exercises, very high state taxes, or significant long-term capital gains — absolutely does, and it can surprise them with a huge, unexpected bill.

How AMT works in principle

You calculate your taxes two ways: the regular way and the AMT way. You pay whichever is higher. The AMT uses a different set of deductions (fewer), different brackets (flatter), and a different set of 'preference items' that add back some deductions or income that the regular system doesn't count. If your AMT calculation produces a higher tax, you owe the difference.

Who actually pays AMT

• People exercising large amounts of Incentive Stock Options (ISOs) — the 'bargain element' at exercise is added to AMT income.
• Households with very high state and local tax deductions (though the 2017 tax reform limited this).
• Some high earners with significant investment income or business deductions.
• Taxpayers whose regular tax happens to be low relative to income because of specific credits or accelerated deductions.

Checking your exposure

Most tax software (TurboTax, H&R Block, etc.) calculates AMT automatically. If you're nervous about a specific situation — exercising options, a big capital gain, a complicated year — run the numbers in tax software before executing the transaction. Five minutes of pre-planning can save five-figure surprises.