Alternative Minimum Tax (AMT) Calculator

How the AMT Calculation Works

The Alternative Minimum Tax calculation runs parallel to your regular tax calculation. You start with your regular taxable income and add back specific items that the AMT disallows as deductions. The most significant add-back is state and local taxes, which are fully disallowed under AMT. Other common add-backs include the spread from exercising incentive stock options, certain itemized deductions, and tax-exempt interest from private activity municipal bonds. The resulting figure is your Alternative Minimum Taxable Income (AMTI). From this, you subtract the AMT exemption, which phases out at higher income levels. The remaining amount is taxed at 26% on the first $232,600 and 28% on amounts above that. This produces the tentative minimum tax. If the tentative minimum tax exceeds your regular income tax, you pay the excess as AMT on top of your regular tax. The 2017 tax reform significantly reduced AMT exposure by capping the SALT deduction at $10,000 for regular tax purposes, eliminating much of the add-back that previously triggered AMT for many upper-middle-class taxpayers.

ISO Exercises and the AMT Trap

The intersection of incentive stock options and the AMT has caught countless technology workers and startup employees off guard, sometimes with devastating financial consequences. When you exercise an ISO, the bargain element, the difference between the exercise price and the current fair market value, is not taxed as regular income but must be added to your AMTI for AMT purposes. If you exercise a large block of ISOs in a single year, this can create an enormous AMT liability even though you have not sold the shares and have no cash to pay the tax. The worst-case scenario occurred during the dot-com crash when employees exercised options, owed AMT on the paper gains, and then watched the stock price collapse to below their exercise price. They owed tax on gains that no longer existed. To manage this risk, consider exercising ISOs gradually over multiple years to spread the AMT impact, selling some shares in the same year to generate cash for taxes, or working with a tax advisor to calculate the maximum number of options you can exercise without triggering AMT in a given year.

Who Needs to Worry About AMT Today

The Tax Cuts and Jobs Act of 2017 dramatically changed the AMT landscape. By nearly doubling the AMT exemption, raising the phaseout thresholds, and capping the SALT deduction at $10,000 for regular tax purposes, the reform reduced the number of AMT-affected taxpayers from about 5 million to roughly 200,000. Today, the taxpayers most likely to owe AMT are those who exercise large amounts of incentive stock options, have significant income from private activity bond interest, have large amounts of accelerated depreciation or intangible drilling costs, or have very high incomes where the AMT exemption phases out. For most upper-middle-class taxpayers who previously triggered AMT primarily through large SALT deductions, the AMT is no longer a concern because the SALT cap limits their regular tax deduction to the same level AMT would have imposed anyway. However, the SALT cap and higher exemptions are scheduled to expire after 2025, which could substantially increase AMT exposure for millions of taxpayers starting in 2026.