The Alternative Minimum Tax is a separate calculation the IRS uses to make sure high-income taxpayers pay at least some federal income tax

The Alternative Minimum Tax (AMT) is a parallel tax system that runs alongside the regular federal income tax. Instead of using the standard tax brackets and deductions, the AMT recalculates your tax liability using its own rules. If your AMT comes out higher than your regular tax, you pay the AMT amount instead. The IRS designed it to prevent wealthy individuals and corporations from using deductions and credits to reduce their tax bill to near zero.

The AMT applies to a much smaller group than it originally did. Congress has adjusted the income thresholds almost every year since 2001 to keep the AMT from hitting middle-income filers. For 2024, the AMT threshold starts at $85,900 for single filers and $133,900 for married couples filing jointly. These numbers change yearly and are adjusted for inflation.

You do not automatically owe AMT just because you earn above these thresholds. The AMT only kicks in if you have enough preference items — certain types of income or deductions that the AMT treats differently than the regular tax code does.

Key Takeaways

  • The AMT recalculates your tax using a separate set of rules and rates, and you pay whichever amount is higher — your regular tax or your AMT.
  • The AMT threshold for 2024 is $85,900 for single filers and $133,900 for married couples filing jointly, adjusted annually for inflation.
  • Common AMT preference items include state and local tax deductions, mortgage interest on loans above $750,000, incentive stock option gains, and certain business deductions.
  • You file Form 6251 with your tax return if you think you might owe AMT, or if your tax software flags you as a potential AMT filer.
  • The AMT rate is a flat 26% or 28% depending on your income level, compared to regular tax brackets that go up to 37%.

What counts as an AMT preference item

The AMT does not disallow deductions entirely — it treats certain deductions differently. The main ones are:

State and local taxes (SALT). Under regular tax rules, you can deduct up to $10,000 in state income tax, property tax, and sales tax combined. The AMT does not allow this deduction at all. If you live in a high-tax state and pay $15,000 in state and local taxes, the AMT adds back $15,000 to your income.

Mortgage interest. Regular tax lets you deduct interest on up to $750,000 in mortgage debt. The AMT only allows interest on $500,000. If you have a $600,000 mortgage, the AMT disallows the interest on the $100,000 above its limit.

Incentive stock options (ISOs). When you exercise an ISO, the difference between the exercise price and the fair market value counts as income for AMT purposes, even if you have not sold the shares yet. This can create a large AMT preference item in the year you exercise.

Certain business and rental deductions. Depreciation, depletion, and some passive activity losses are treated more restrictively under AMT rules than under regular tax rules.

How the AMT calculation works

The AMT starts with your adjusted gross income (AGI) and adds back preference items to get your alternative minimum taxable income (AMTI). You then subtract the AMT exemption amount, apply the AMT tax rate to what remains, and calculate your tentative minimum tax.

The AMT exemption amounts for 2024 are $85,900 for single filers and $133,900 for married couples filing jointly. These exemptions phase out at higher income levels — for every dollar of AMTI above the threshold, you lose 25 cents of the exemption. This phase-out can make the AMT bite harder for very high earners.

The AMT tax rate is 26% on the first portion of your AMTI above the exemption, and 28% on amounts above that threshold. These rates are lower than the top regular tax rate of 37%, but because the AMT exemption is smaller and preference items add back deductions, the AMT often produces a higher total tax bill.

You compare your tentative minimum tax to your regular tax liability. Whichever is higher is what you owe to the IRS. If the AMT is higher, you pay the difference as additional tax.

Who is most likely to owe AMT

The AMT most commonly affects high-income earners in states with high state and local taxes, people who exercise large numbers of stock options, and those with significant rental or business income. A single filer earning $200,000 in California or New York is far more likely to owe AMT than a single filer earning $200,000 in Texas or Florida, because of the SALT preference item.

Executives and employees at growth-stage companies who receive and exercise ISOs can face a large AMT bill in the year they exercise, even if they do not sell the shares. This has caught many people off guard — they owe AMT tax on paper gains they have not yet realized in cash.

Self-employed people and real estate investors can also trigger AMT through depreciation and other business deductions that the AMT treats more strictly. The interaction between regular tax and AMT rules is complex enough that most people in these situations benefit from working with a tax professional.

Filing Form 6251 and reporting AMT

If you think you might owe AMT, you file Form 6251 (Alternative Minimum Tax — Individuals) along with your regular Form 1040. Most tax software will prompt you to file Form 6251 if your income or deductions cross certain thresholds, or if you have known preference items like ISOs.

Form 6251 walks through the calculation: it starts with your AGI, adds back preference items, subtracts the exemption, applies the tax rate, and compares the result to your regular tax. If the AMT is higher, the form tells you how much additional tax to pay.

You do not need to file Form 6251 if your regular tax is clearly higher than any AMT you could owe. However, if you are close to the threshold or have significant preference items, filing it protects you — if you do not file and the IRS later determines you owed AMT, you will owe penalties and interest on top of the tax.

AMT credits and carryforwards

If you pay AMT in one year, you may be able to use an AMT credit in future years to reduce your regular tax. The credit only applies to AMT you paid on "deferral items" — deductions that are timing differences rather than permanent differences. SALT and mortgage interest are permanent differences, so they do not generate credits. ISOs and depreciation are deferral items, so they do.

The AMT credit can be carried forward indefinitely, but it can only offset regular tax that exceeds your tentative minimum tax in future years. This means if you owe AMT one year because of ISOs, you might recover some of that tax in later years when your income is lower or your preference items are smaller. The mechanics are complex, and most people need professional help to track and use AMT credits correctly.

Planning around AMT

If you know you will owe AMT, a few strategies can help. Timing the exercise of stock options across multiple years can spread the preference item over time and reduce the AMT hit in any single year. Bunching charitable donations or other deductions into years when you do not expect to owe AMT can also help, though the benefit is limited because the AMT does not allow many deductions anyway.

For people with high SALT, the $10,000 cap under regular tax rules means the AMT preference item is often unavoidable. Some states have created workarounds like pass-through entity taxes, which shift the tax burden in ways that can reduce AMT exposure, but these strategies are state-specific and require professional guidance.

The most important step is knowing whether you are likely to owe AMT before the year ends. If you are, a tax professional can model different scenarios and help you make decisions about timing of income, deductions, and option exercises that actually move the needle.

Frequently Asked Questions

Can I avoid AMT by taking fewer deductions?

Not entirely. The AMT adds back certain deductions regardless of whether you take them, so reducing deductions does not always reduce AMT. SALT is added back in full, and mortgage interest above $500,000 is added back. However, reducing discretionary deductions like charitable contributions can help. A tax professional can model your specific situation.

Do I owe AMT if I am below the income threshold?

Rarely. The AMT threshold is designed to catch people with high incomes and large preference items. If your income is below $85,900 (single) or $133,900 (married), you almost certainly do not owe AMT. The threshold is adjusted yearly for inflation.

What happens if I exercise stock options and owe AMT?

You owe AMT tax on the spread (the difference between the exercise price and fair market value) in the year you exercise, even if you do not sell the shares. This can create a large tax bill with no cash to pay it. You may be able to use an AMT credit in future years to recover some of the tax, but the timing and amount depend on your future income and tax situation.

Does the AMT apply to capital gains?

Capital gains are taxed at the same preferential rates under both regular tax and AMT rules, so they do not create an AMT preference item by themselves. However, if you have other preference items that push you into AMT, your capital gains are taxed as part of your AMTI at the AMT rates.

Should I hire a tax professional if I think I owe AMT?

If your income is high, you have stock options, you live in a high-tax state, or you own rental property, a tax professional can help you understand whether AMT applies and model strategies to reduce it. The cost of professional help is often far less than the tax you can save through proper planning.