Written by the TaxPlain Editorial Team · Reviewed for accuracy · Last updated August 2026
⚠️ Educational only. TaxPlain does not provide tax, legal, or financial advice. Always consult a qualified tax professional about your specific situation.
What this is
The Alternative Minimum Tax (AMT) is a separate tax calculation that runs alongside your regular tax return. It exists to make sure high earners who claim a lot of deductions and preference items still pay a minimum amount of tax, even after those write-offs.
Here's how it works: the IRS recalculates your income under a stricter set of rules, adding back certain deductions that reduce your regular taxable income. This recalculated figure is called alternative minimum taxable income, or AMTI. You then subtract an AMT exemption amount and apply a flat rate — 26% or 28% — to what's left.
You compare that result to your regular tax bill and pay whichever number is higher. For most taxpayers, regular tax wins and AMT never comes into play. But for people with large capital gains, high state and local tax deductions, or incentive stock option exercises, AMT can quietly become the bigger bill.
Who it affects
✓ Most likely to owe AMT
Taxpayers who exercised incentive stock options (ISOs) and held the shares, or who claim very large state and local tax deductions relative to their income.
↑ Also worth checking
Households with significant long-term capital gains, certain depreciation deductions, or private-activity bond interest.
📅 2026 EXEMPTION AND PHASE-OUT AMOUNTS
For the 2026 tax year, the AMT exemption is $90,100 for single/head of household filers, $140,200 for married couples filing jointly, and $70,100 for married filing separately. The exemption starts phasing out once your AMTI passes $500,000 (single) or $1,000,000 (joint) — and under the One Big Beautiful Bill Act, that phase-out now happens twice as fast as it did in 2025, at 50 cents lost for every dollar of income above the threshold.
How it's calculated
From taxable income to AMT liability
You calculate AMT on Form 6251, which walks through a specific sequence. Start with your AGI, add back the preference items and adjustments listed below, subtract your exemption amount, then apply the AMT rate.
Standard deduction — not allowed under AMT; it gets added back to your income.
State and local tax (SALT) deduction — added back in full, which is why high-SALT states see more AMT exposure.
ISO exercise spread — the difference between the exercise price and fair market value on incentive stock options counts as AMT income the year you exercise, even if you haven't sold the shares.
Certain depreciation — some accelerated depreciation methods get recalculated more conservatively under AMT rules.
Private-activity bond interest — normally tax-exempt, but it's added back for AMT purposes.
Exemption amount — subtracted after add-backs, using the 2026 figures above.
After the exemption, a 26% rate applies to the first $244,500 of remaining AMTI, and 28% applies above that. Whatever this comes out to gets compared against your regular tax — you pay the higher of the two.
Related forms often involved
AMT rarely shows up alone — it's usually triggered by, or interacts with, one of these forms.
Form 6251 — the form used to calculate whether you owe AMT and how much.
Form 8801 — used in a later year to claim back some AMT you paid due to timing differences, like an ISO exercise.
Form 8949 and Schedule D — capital gains reported here can also affect your AMTI, especially large gains in a single year.
Form 1099-B — reports the stock sale proceeds that often accompany an ISO exercise, which is one of the most common AMT triggers.
Common mistakes to avoid
⚠️ Exercising ISOs without checking AMT first
Exercising and holding incentive stock options can trigger a large AMT bill in the year of exercise, even though you haven't sold anything or received cash. Model the AMT impact before you exercise, not after.
⚠️ Assuming AMT no longer applies to you
Because far fewer people owe AMT since the exemption amounts were raised, some taxpayers stop checking altogether. The 2026 phase-out changes bring more high earners back into range than in recent years.
What to do right now
If you exercised ISOs this year, have significant capital gains, or claim a large SALT deduction, run Form 6251 before you file — most tax software does this automatically, but it's worth confirming. If you're close to the phase-out thresholds, compare your AGI and MAGI figures against the 2026 numbers above to see how close you actually are.
Questions to ask your tax professional
01Based on my income and deductions, am I likely to owe AMT this year?
02If I exercise incentive stock options, how much AMT exposure would that create?
03Do I have a minimum tax credit from a prior year that I can claim on Form 8801?
04Would spreading a large capital gain or ISO exercise across two tax years reduce my AMT risk?
05How do the 2026 phase-out changes affect my specific situation compared to last year?
Frequently asked questions
What is the AMT exemption amount for 2026?
For the 2026 tax year, the AMT exemption is $90,100 for single and head of household filers, $140,200 for married couples filing jointly, and $70,100 for married filing separately. If your alternative minimum taxable income is at or below your exemption amount, you owe no AMT.
What income triggers the AMT?
AMT is most often triggered by exercising incentive stock options, claiming large state and local tax deductions, having significant long-term capital gains, or certain depreciation add-backs. These items get added back into your income under the AMT's alternative calculation, which can push your AMTI above the exemption amount.
How do I know if I owe AMT?
You calculate your AMT liability on IRS Form 6251, which recalculates your income under AMT rules and compares the result to your regular tax. Most tax software runs this calculation automatically. You only owe the difference if your AMT liability is higher than your regular tax.
What's the difference between AMT and regular tax?
Regular tax uses your normal deductions and a graduated bracket system. AMT uses a separate calculation called alternative minimum taxable income, which adds back certain deductions and preference items, then applies a flat 26% or 28% rate after subtracting your exemption. You pay whichever amount is higher.
Can I get back AMT I paid in a prior year?
In some cases, yes. If you paid AMT in a prior year due to timing differences like ISO exercises, you may be able to claim a minimum tax credit in a later year using Form 8801. This doesn't apply to all AMT triggers, so it's worth reviewing with a tax professional.