Alternative Minimum Tax (AMT): What It Is and How It Works

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The alternative minimum tax (AMT) is a parallel federal income tax calculation in the United States. It adds back certain deductions and tax preferences to your income, subtracts a fixed exemption, applies flat rates of 26% and 28%, and requires you to pay whichever is higher: your regular income tax or this alternative figure. The design sets a floor so that taxpayers who claim large deductions and preferential items still pay a minimum level of tax.

How the Alternative Minimum Tax Works

The calculation runs in four steps.

1. Start with alternative minimum taxable income (AMTI). Begin with regular taxable income and add back items the AMT does not allow. The standard deduction is not permitted under the AMT, and itemized deductions for state and local taxes are added back. Other common adjustments include the bargain element of exercised incentive stock options, interest on certain private activity municipal bonds, and differences in depreciation methods.
2. Subtract the exemption. For 2026 the exemption is $90,100 (single) and $140,200 (married filing jointly), up from $88,100 and $137,000 in 2025.
3. Apply the phaseout if income is high. The exemption shrinks by $0.25 for every dollar of AMTI above the threshold. In 2026 those thresholds are $500,000 for single filers and $1,000,000 for joint filers, sharply lower than the 2025 thresholds of $626,350 and $1,252,700. At those rates, a single filer’s 2026 exemption is fully eliminated at an AMTI of $860,400.
4. Apply the rates. The amount left after the exemption is taxed at 26% up to $244,500 in 2026 ($122,250 for married filing separately) and 28% above that. Long-term capital gains and qualified dividends keep their preferential rates inside the AMT calculation.

The result is the tentative minimum tax. If it exceeds your regular tax, the difference is added to your bill as AMT. If it does not, you owe no AMT.

Interpreting the result

A high income alone does not trigger the AMT. The gap between the two calculations does. A wage earner who takes the standard deduction often has an AMTI close to regular taxable income, and the exemption keeps the tentative minimum tax below the regular tax. The AMT tends to apply when large add-backs, such as big state tax deductions or incentive stock option exercises, open a wide gap between regular taxable income and AMTI.

Example of the Alternative Minimum Tax

Hypothetical example, 2026 rules, single filer. Assume the AMTI after add-backs is $300,000, and assume the regular tax liability works out to $50,000.

• AMTI is below $500,000, so the full $90,100 exemption applies.
• Amount subject to AMT rates: $300,000 − $90,100 = $209,900.
• All of it falls under the $244,500 threshold: $209,900 × 26% = $54,574.
• The tentative minimum tax ($54,574) exceeds the regular tax ($50,000), so the taxpayer owes $4,574 of AMT, for a total of $54,574.

Hypothetical phaseout case, same filer type. With an AMTI of $600,000, the exemption drops by 25% × $100,000 = $25,000, leaving $65,100. The remaining $534,900 is taxed at 26% on the first $244,500 ($63,570) and 28% on the other $290,400 ($81,312), for a tentative minimum tax of $144,882. That figure is then compared against the regular tax.

Why the AMT Exists: A Brief History

Congress passed the first minimum tax in 1969 after it emerged that 155 high-income households had paid no federal income tax in 1966. Repealing the breaks they combined would have hit taxpayers at every income level, so lawmakers added a second calculation aimed at people who used them heavily.

For decades the exemption was not indexed, so rising nominal incomes pushed more middle-income households into the AMT. The American Taxpayer Relief Act of 2012 permanently indexed it to inflation. The Tax Cuts and Jobs Act, effective 2018, raised the exemption and phaseout thresholds, eliminated personal exemptions and miscellaneous itemized deductions, and capped the state and local tax deduction. Together these changes removed items that had most often triggered the AMT. The lower 2026 phaseout thresholds reverse part of that expansion for high earners.

Do You Owe the AMT?

A rough screen: subtract the AMT exemption for your filing status from your taxable income with the add-back items included. If the result is zero or negative, the AMT cannot apply. If it is positive, complete IRS Form 6251, usually through tax software or a preparer, to determine whether you owe the tax and how much. If you do, attach the form to the return you file with the IRS.

Limitations and Common Confusions

AMT vs. the AMT credit (AMTC). Some adjustments, such as incentive stock options and depreciation, only change when income is taxed. AMT paid because of these timing items can generate a minimum tax credit, claimed on Form 8801, that reduces regular tax in later years when the regular tax exceeds the tentative minimum tax. AMT caused by permanent items like the state tax add-back does not create a credit.

AMT bonds. Interest on certain private activity municipal bonds is exempt from regular tax but counts as AMT income. Municipal funds labeled “AMT-free” avoid these bonds.

AMTI vs. other income measures. AMTI is not the same as gross income, adjusted gross income or MAGI. Each starts from a different point and serves a different set of rules.

Individual vs. corporate AMT. The Inflation Reduction Act of 2022 created a separate 15% corporate alternative minimum tax based on financial statement income for very large corporations. It works differently from the individual AMT described here.

The main drawback of the individual AMT is complexity. Taxpayers effectively compute their tax twice, and timing choices such as exercising stock options or prepaying state taxes can change the outcome in ways that are hard to see without running both calculations.

The Bottom Line

The AMT matters most to taxpayers with large add-backs, such as big state tax deductions, incentive stock option exercises, or private activity bond interest, and to high earners facing the lower 2026 phaseout thresholds. A wide gap between regular taxable income and AMTI, rather than high income alone, triggers the tax. Anyone whose income after the exemption is positive should complete Form 6251 and test timing choices before acting.