What Is Form 6251: Alternative Minimum Tax for Individuals

Form 6251 is the IRS form individuals use to calculate the Alternative Minimum Tax, a parallel tax system that makes sure higher-income filers pay at least a minimum amount of federal income tax after certain deductions and exclusions are stripped back out. You attach it to Form 1040 when your income, recalculated under AMT rules, produces a higher tax than your regular return. For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, and the exemption phases out faster than it did in prior years because of changes in the One Big Beautiful Bill Act.¹

Who Needs to File Form 6251

You need Form 6251 when your taxable income, after adding back certain adjustments and preference items, exceeds the AMT exemption for your filing status. Most tax software runs the calculation automatically and attaches the form when needed, but knowing the triggers helps you plan before filing season rather than finding out at the last minute.

The most common triggers:

A large state and local tax deduction. The full SALT deduction you claimed on your regular return gets added back for AMT.
Exercising incentive stock options. The spread between your exercise price and the stock’s fair market value counts as AMT income in the year you exercise.²
Private activity bond interest. Tax-exempt interest from certain municipal bonds issued for non-governmental purposes is taxable under the AMT.³
Accelerated depreciation on business or rental property. AMT forces a slower schedule, creating a positive adjustment in early years.

Even if you don’t owe AMT, you may still need to file Form 6251 to document that your regular tax exceeds the tentative minimum tax. That matters when you’re carrying forward a minimum tax credit from a prior year.

How the Form 6251 Calculation Works

The AMT calculation on Form 6251 follows a straightforward sequence, even when the adjustments themselves get complicated:

Start with your regular taxable income from Form 1040.
Add back AMT adjustments and preference items (SALT, ISO spread, private activity bond interest, depreciation differences, and others).
Subtract any negative adjustments where AMT treatment is more favorable than regular tax treatment.
The result is your Alternative Minimum Taxable Income (AMTI).
Subtract the AMT exemption, reduced by any phase-out.
Apply the AMT rates (26% and 28%) to what’s left. That gives you the Tentative Minimum Tax.
Compare the tentative minimum tax to your regular tax. If it’s higher, the difference is your AMT, added on top of your regular tax.

If your regular tax already exceeds the tentative minimum tax, you owe no AMT. Most filers land there. The AMT only bites when specific add-backs push your AMTI far enough above your regular taxable income that the tentative minimum tax overtakes it.⁴

2026 AMT Exemption Amounts and Phase-Out

The exemption is the amount of AMTI shielded from the tax. For 2026:

Single or head of household: $90,100 exemption, phase-out begins at $500,000 of AMTI.
Married filing jointly: $140,200 exemption, phase-out begins at $1,000,000 of AMTI.
Married filing separately: $70,100 exemption, phase-out begins at $500,000 of AMTI.

These figures are adjusted annually for inflation.¹

Starting in 2026, the exemption phases out at 50 cents for every dollar of AMTI above the threshold. That’s twice the 25-cent rate that applied through 2025.⁵ A married couple’s $140,200 exemption is completely gone once AMTI reaches roughly $1,280,400. Under the old phase-out speed, the exemption would have survived until about $1,560,800. Inside the phase-out range you’re effectively paying AMT on both the added income and the shrinking exemption, which pushes the real rate above the statutory 26% or 28%.

AMT Tax Rates for 2026

The AMT uses two rate tiers rather than the seven brackets in the regular income tax system. For 2026, after subtracting your exemption from AMTI:

26% on the first $244,500 ($122,250 if married filing separately).
28% on amounts above that.

These rates are lower than the top regular rate, but they apply to a broader income base because so many deductions are disallowed. Long-term capital gains and qualified dividends keep the same preferential rates under both systems, so investment income taxed at 15% or 20% for regular purposes stays there under the AMT.

In the exemption phase-out zone the effective rate is higher than the statutory rates suggest. Every additional dollar of AMTI eliminates 50 cents of exemption that would otherwise have been tax-free, so the real marginal rate in the phase-out range can reach roughly 42% on the portion in the 28% tier. That’s where AMT hits hardest.

The Adjustments and Preferences That Most Often Cause AMT

Form 6251 works by taking your regular taxable income and modifying it. Certain deductions get added back. Certain excluded income items get added in. These modifications split into two categories: adjustments (which can be positive or negative) and preference items (which only increase AMTI). The distinction matters for the minimum tax credit.

State and Local Taxes

The SALT deduction is the single most common reason taxpayers owe AMT. Under the regular system you can deduct state and local income, sales, and property taxes as an itemized deduction. Under the AMT the entire SALT deduction is disallowed, so every dollar you deducted gets added back.⁶

This creates an especially large adjustment for 2026. The One Big Beautiful Bill Act raised the regular-tax SALT cap from $10,000 to roughly $40,000, so the gap between what you deduct for regular tax and what’s allowed for AMT purposes widened. If you paid $35,000 in state and local taxes in 2025, your AMT adjustment was capped at $10,000 (the maximum you could deduct). In 2026 you can deduct more of that $35,000 for regular tax but still get zero credit for it under the AMT. The result is a bigger adjustment and a higher chance of owing.

SALT is an exclusion item. It permanently increases your AMT income; there’s no future year where the deduction reverses. AMT paid because of the SALT add-back does not generate a minimum tax credit.

Incentive Stock Options

ISOs are a frequent AMT trigger for employees at technology and startup companies. For regular tax purposes, exercising an ISO isn’t a taxable event. You owe regular tax only when you eventually sell the shares. But the AMT treats the exercise itself as income: the difference between the stock’s fair market value at exercise and the price you paid (the bargain element) is added to AMTI.²

This feels like a tax on money you never received. You haven’t sold, you have no cash proceeds, and yet you owe AMT on a paper gain. If the stock price drops after you exercise, you can end up owing AMT on a gain that has evaporated. That scenario hurt many employees during the 2000 dot-com crash and remains one of the most punishing AMT traps.

There is an escape valve. If you sell the stock in the same calendar year you exercise, the transaction is treated as a disqualifying disposition. No AMT adjustment is required, because the gain or loss is recognized for regular tax purposes in the same year. Advisors often recommend same-year exercises and sales when the AMT hit would otherwise be severe.

Unlike SALT, the ISO adjustment is a timing difference. The income will eventually be taxed under the regular system when you sell. AMT paid on ISO adjustments therefore generates a minimum tax credit you can carry forward.

Depreciation

If you own rental property or business assets and use accelerated depreciation under the regular system, the AMT requires a slower schedule, generally the 150% declining balance method switching to straight-line when that produces a larger deduction.⁶ In early years, regular depreciation exceeds AMT depreciation, so you add the difference back. Later years flip: AMT depreciation exceeds the regular amount, creating a negative adjustment. Over the asset’s life, total depreciation is identical under both systems. Only the timing differs, so depreciation-related AMT qualifies for the minimum tax credit.

Private Activity Bond Interest

Interest from most municipal bonds is exempt from federal income tax. Interest from certain private activity bonds, meaning those that finance non-governmental projects like sports stadiums, industrial developments, or airport terminals, must be included in AMTI.⁷ The interest still remains tax-free for regular income tax purposes under Section 103.⁸ This is an exclusion item, not a timing difference. Your brokerage statement or Form 1099-INT will typically flag which bonds fall into this category.

Foreign Tax Credit

If you claim a foreign tax credit, you have to recalculate it separately for AMT purposes using AMT income and deduction amounts. The credit often comes out different, which can increase your tentative minimum tax.⁴

The Minimum Tax Credit

Paying AMT doesn’t always mean the money is gone for good. The minimum tax credit reimburses you for AMT paid on timing differences, situations where income was simply taxed sooner under the AMT than it would have been under the regular system. You claim it on Form 8801.⁹

Timing differences include ISO adjustments and depreciation differences. In a future year when your regular tax exceeds your tentative minimum tax, the credit reduces your regular tax. It carries forward indefinitely, so you don’t lose it if your situation doesn’t reverse right away.¹⁰

Exclusion items, meaning SALT and private activity bond interest, do not generate a minimum tax credit. Those adjustments represent income that the regular tax system permanently excludes, so there’s no future reversal to reimburse. If most of your AMT comes from SALT, the credit won’t help you recover it.

What Changed for 2026 Under the One Big Beautiful Bill Act

The Tax Cuts and Jobs Act of 2017 temporarily raised AMT exemption amounts and phase-out thresholds, which shielded millions of taxpayers from the AMT. Those provisions were set to expire after 2025, which would have dropped exemptions back to much lower levels and dramatically expanded AMT exposure. The One Big Beautiful Bill Act, signed into law in 2025, prevented that cliff but added its own twist.

The law permanently keeps the higher exemption amounts from the TCJA, indexed for inflation. For 2026 that means the $90,100 single and $140,200 joint exemptions remain in place rather than falling to roughly $60,000 and $95,000.⁵

The trade-off is the doubled phase-out rate, now 50% instead of 25%. The exemption vanishes twice as quickly once AMTI crosses the threshold. A married couple’s exemption is fully gone at roughly $1.28 million of AMTI, compared to about $1.56 million under the old speed. Filers in the $500,000 to $1.3 million AMTI range should pay close attention, because that’s where the accelerated phase-out hits hardest. Combine that with the larger SALT add-back created by the higher regular-tax cap, and 2026 will pull some households back into AMT territory who cleared it easily under prior rules.¹

1
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
2
Internal Revenue Service. Instructions for Form 6251
3
Internal Revenue Service. Form 6251 – Alternative Minimum Tax – Individuals
4
Internal Revenue Service. Instructions for Form 6251 – Alternative Minimum Tax – Individuals
5
Office of the Law Revision Counsel. 26 USC 55 – Alternative Minimum Tax Imposed
6
Office of the Law Revision Counsel. 26 USC 56 – Adjustments in Computing Alternative Minimum Taxable Income
7
Office of the Law Revision Counsel. 26 USC 57 – Items of Tax Preference
8
Office of the Law Revision Counsel. 26 U.S. Code 103 – Interest on State and Local Bonds
9
Internal Revenue Service. Instructions for Form 8801
10
Internal Revenue Service. Form 8801 – Credit for Prior Year Minimum Tax – Individuals, Estates, and Trusts