AMT Exemption Phaseout Calculator
The Alternative Minimum Tax exemption shields part of your alternative minimum taxable income (AMTI) from the AMT, but it phases out by 25 cents for every dollar of AMTI above a threshold that depends on filing status. This calculator takes your AMTI, the year's exemption amount, and the phaseout threshold, then shows how much exemption remains, how much was phased out, and your resulting AMT base. Look up the current exemption and threshold in the Form 6251 instructions and enter them for an accurate result.
AMT exemption phaseout formula
Excess = max(0, AMTI - threshold)
Exemption phased out = min(exemption, 0.25 * excess)
Remaining exemption = exemption - exemption phased out
AMT base = max(0, AMTI - remaining exemption)
AMTI at full phaseout = threshold + (exemption / 0.25)
The exemption falls by 25 cents per dollar of AMTI over the threshold and cannot go below zero. Once AMTI reaches the full-phaseout point, the AMT base equals the entire AMTI.
AMT exemption context
- The exemption and threshold are inflation-adjusted yearly and differ by filing status.
- The phaseout rate is 25 cents per dollar of AMTI above the threshold.
- AMTI adds back preference items such as certain ISO spreads and state tax deductions.
- AMT rates are 26 percent up to a breakpoint and 28 percent above it, applied to the AMT base.
- You owe AMT only when tentative minimum tax exceeds your regular tax liability.
AMT exemption: frequently asked questions
How does the AMT exemption phaseout work?
The Alternative Minimum Tax (AMT) exemption is reduced by 25 cents for every dollar that alternative minimum taxable income (AMTI) exceeds the phaseout threshold for your filing status. Once AMTI is high enough, the exemption is fully phased out. This is set in Internal Revenue Code Section 55 and reported on Form 6251.
Where do I get the exemption and threshold amounts?
The IRS adjusts the AMT exemption amounts and phaseout thresholds for inflation each year, and they differ by filing status (single, married filing jointly, married filing separately). Look up the current figures in the Form 6251 instructions or the annual inflation-adjustment release, then enter them here.
What is alternative minimum taxable income?
AMTI is your taxable income recomputed under AMT rules, adding back certain preference items and adjustments (such as some state tax deductions and incentive stock option spreads) that are allowed for regular tax. Form 6251 walks through the adjustments. Enter your computed AMTI to find your remaining exemption.
What is the AMT base after the exemption?
The AMT base is AMTI minus the remaining exemption. It is the amount to which the AMT rates (26 percent up to a breakpoint, then 28 percent) are applied to find tentative minimum tax. You owe AMT only if the tentative minimum tax exceeds your regular tax. This calculator shows the base; apply the AMT rates separately.
Why might my exemption be fully phased out?
If your AMTI exceeds the threshold by four times the exemption amount, the 25 percent reduction eliminates the entire exemption. For example, if the exemption is $85,700 and the threshold is $609,350, the exemption reaches zero once AMTI is about $952,150 higher than the threshold base. After that point your AMT base equals your full AMTI.
Official sources
- U.S. Internal Revenue Service: About Form 6251, Alternative Minimum Tax.
- U.S. Internal Revenue Service: IRS Newsroom (inflation adjustments).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.