What Is the Alternative Minimum Tax (AMT) and Could You Owe It?

The Alternative Minimum Tax (AMT) is a second, parallel way of calculating your federal income tax. You calculate your tax bill twice — once under the regular rules, once under AMT rules — and pay whichever amount is higher. It was created to stop very high earners from using deductions to reduce their tax bill to almost nothing.

How the AMT Calculation Differs

The AMT calculation starts from your regular taxable income, then adds back certain deductions and exemptions that regular tax rules allow but AMT rules don't — most commonly the state and local tax (SALT) deduction, and in some cases the exercise of incentive stock options. The result is taxed at a flat 26% or 28% rate (versus the regular system's graduated brackets), but only after subtracting a large AMT exemption amount.

Who Actually Gets Hit by It

After a major overhaul in 2017 that raised the AMT exemption significantly, far fewer taxpayers owe it than a decade ago. Today it mostly affects people in high-tax states with large SALT deductions, people who exercise significant incentive stock options (ISOs) in a single year, and households with large numbers of dependents or unusual deduction patterns that don't carry over to the AMT calculation.

The ISO Trap

The most common way ordinary employees stumble into AMT is exercising incentive stock options and holding the shares rather than selling immediately. The spread between the strike price and the market value at exercise counts as income for AMT purposes even though you haven't sold anything and received no cash — meaning you can owe real tax on a stock position that could still lose value before you sell.

Do You Need to Worry About It?

Most tax software calculates both versions automatically and applies whichever is higher, so you don't need to compute it by hand. The situations worth actively planning around are: exercising a large batch of ISOs, living in a high-tax state with a large SALT deduction, or having unusually large itemized deductions relative to your income. In those cases, it's worth running the numbers — or having a tax professional run them — before year-end, since ISO exercise timing in particular can be adjusted.