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Alternative Minimum Tax (AMT) Calculator

Estimate whether you owe Alternative Minimum Tax by comparing your AMT liability to your regular tax.

Result

Tentative Minimum Tax
$42,718.00
Additional AMT Owed
$0.00
AMT Exemption Applied
$85,700.00

Uses 2025 AMT exemption amounts and phase-out thresholds. AMT works as a parallel tax system: if your Tentative Minimum Tax exceeds your regular tax, you pay the difference as AMT on top of your regular tax. This is a simplified estimate - a full AMT calculation (Form 6251) includes many specific addback items not modeled here.

About the AMT Calculator

The Alternative Minimum Tax Calculator estimates whether you owe AMT by running your income through the parallel AMT system, which uses a broader income base, a fixed exemption, and its own two-tier rate structure, then comparing the result to your regular federal tax. It is designed for higher earners with significant deductions or preference items, such as large state and local tax deductions or exercised incentive stock options, who want to check whether AMT applies to them before filing. Because AMT only applies when the parallel calculation exceeds your regular tax, the calculator's core output is the extra amount, if any, you would owe on top of what you already calculated.

How It Works

You select your filing status and enter your AMT taxable income, AMTI, meaning your regular taxable income plus common AMT addbacks, along with your regular federal tax before credits. The calculator applies a filing-status-specific exemption that phases out as AMTI rises past a threshold, applies AMT's two-tier rate to what remains, and compares that Tentative Minimum Tax to your regular tax. If the AMT figure is higher, the difference is the additional AMT you owe.

Exemption = max(Base Exemption - max(AMTI - Phase-out Threshold, 0) x 0.25, 0); AMT Base = max(AMTI - Exemption, 0); Tentative Minimum Tax = AMT Base x 0.26 if AMT Base <= $232,600, else $232,600 x 0.26 + (AMT Base - $232,600) x 0.28; AMT Owed = max(Tentative Minimum Tax - Regular Tax, 0)

Formula & Methodology

The 2025 exemption used here is $85,700 for single filers and $133,300 for married filers, and it starts phasing out once AMTI passes $609,350 for single filers or $1,218,700 for married filers, reducing by 25 cents for every dollar of AMTI above that threshold until it reaches zero. Whatever exemption remains is subtracted from AMTI to get the AMT base, which is taxed at 26% up to $232,600 and 28% on any amount above that. The resulting Tentative Minimum Tax is then compared to your regular tax; you only pay AMT if the tentative figure is higher, in which case the difference is added on top of your regular tax bill.

Examples

Default Single Filer

With the calculator's defaults - single filing status, $250,000 AMTI, and $45,000 regular tax - the full $85,700 exemption applies since AMTI is well under the $609,350 phase-out threshold, leaving a $164,300 AMT base taxed at 26% for a $42,718 Tentative Minimum Tax, which is below the $45,000 regular tax, so no additional AMT is owed.

High-Income Filer with ISO Exercise

A single filer with $700,000 AMTI, partly from exercising incentive stock options, and $130,000 regular tax sees the exemption reduced to about $63,038 by the phase-out, pushing the AMT base to roughly $636,963; taxed at 26% and 28% across the threshold, the Tentative Minimum Tax comes to about $173,698, roughly $43,698 more than the regular tax, which becomes the additional AMT owed.

Advantages

  • Runs the full AMT exemption phase-out and two-tier rate structure so you do not have to work through Form 6251's mechanics by hand for a quick estimate.
  • Directly answers the practical question of whether Tentative Minimum Tax exceeds regular tax, rather than just showing an isolated AMT number.
  • Shows how much of your exemption survives the phase-out, which helps explain why AMT liability rises faster than income alone would suggest at higher AMTI levels.

Common Mistakes

  • Entering regular taxable income instead of AMTI, which is regular taxable income plus specific addbacks like the SALT deduction and ISO exercise spread.
  • Overlooking the exemption phase-out at higher income and assuming the full base exemption still applies once AMTI is well above the phase-out threshold.
  • Forgetting that AMT is compared against regular tax before credits, and mixing up gross tax figures with post-credit tax liability when entering the regular tax input.

Edge Cases to Watch For

  • If AMTI is high enough that the phase-out subtracts more than the full base exemption, the exemption is floored at zero rather than going negative.
  • The tool assumes AMTI already includes common addbacks like the state and local tax deduction and ISO exercise gains; it does not compute those addbacks itself from raw income and deductions.
  • If your Tentative Minimum Tax comes out below your regular tax, additional AMT owed is floored at zero, since AMT never reduces your tax below the regular amount.

Common Use Cases

  • High-income taxpayers with large state and local tax deductions checking whether they are likely to owe AMT this year.
  • Employees who exercised incentive stock options and need to estimate the AMT impact of the exercise before year-end tax planning.
  • Tax preparers giving clients a quick before-filing estimate of potential AMT exposure.
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

Why does AMT exist alongside the regular tax system?

AMT was created to ensure high earners with substantial deductions and preference items (like large state tax deductions or exercised incentive stock options) still pay a meaningful minimum amount of tax, by recalculating income under a parallel system with fewer deductions and a flatter rate structure, then requiring you to pay whichever amount (regular tax or AMT) is higher.

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Conclusion

AMT works by requiring you to pay whichever is higher, your regular tax or this parallel Tentative Minimum Tax, and this calculator estimates that comparison using the 2025 exemption and rate figures. A full Form 6251 filing involves additional addback items this simplified version does not model, so treat the result as a directional estimate.

References