The Alternative Minimum Tax is a separate tax calculation that some higher-income taxpayers must pay instead of the regular income tax

The Alternative Minimum Tax (AMT) is a parallel tax system run by the IRS. Instead of calculating what you owe using the standard tax brackets and deductions, the AMT recalculates your tax bill using its own rules. If the AMT amount is higher than your regular tax, you pay the AMT instead. It exists because Congress wanted to may support that high-income earners pay at least some minimum amount of tax, even when they use legal deductions and credits to reduce their regular tax bill.

The AMT applies to a smaller group of taxpayers than it did when it was created in 1969, because Congress has raised the income thresholds over time. For 2024, the AMT threshold is roughly $85,900 for single filers and $133,900 for married couples filing jointly, though these numbers change each year. If your income falls below these thresholds, you almost certainly do not owe AMT. If it is above them, you may need to calculate whether AMT applies to you.

Key Takeaways

  • The AMT is a second tax calculation that applies when your income exceeds certain thresholds, currently around $85,900 for single filers and $133,900 for married couples.
  • Under AMT rules, many common deductions (like state and local taxes, mortgage interest on second homes, and miscellaneous itemized deductions) are reduced or eliminated.
  • You calculate both your regular tax and your AMT, then pay whichever is higher.
  • Certain income sources, like incentive stock options and private activity bond interest, trigger AMT more often than others.

How the AMT calculation works

The AMT starts with your regular adjusted gross income (AGI) and then adds back certain deductions and income items that the AMT does not allow. These add-backs are called AMT adjustments. Common adjustments include state and local income taxes (SALT), property taxes, mortgage interest on second homes, and the standard deduction itself.

Once you add these items back, you arrive at Alternative Minimum Taxable Income (AMTI). You then subtract the AMT exemption amount — which is $85,900 for single filers and $133,900 for married couples filing jointly in 2024 — and explore a flat 26% or 28% tax rate to what remains. The result is your tentative AMT. If this number is higher than your regular income tax, you owe the difference as additional tax.

The IRS provides Form 6251 to calculate whether you owe AMT. Most tax software will run this calculation automatically if your income is high enough to trigger it. You do not need to file Form 6251 unless you actually owe AMT, but many taxpayers in the borderline range file it to document that they do not.

Which deductions disappear or shrink under AMT

The AMT disallows or limits deductions that are allowed under regular tax. State and local income taxes (SALT) are completely disallowed under AMT, even though you can deduct up to $10,000 of them on your regular return. Property taxes are also disallowed. Miscellaneous itemized deductions — such as unreimbursed employee expenses and tax preparation fees — are not allowed under AMT at all.

Mortgage interest on a primary home is allowed under both systems, but mortgage interest on a second home or home equity loan is disallowed under AMT unless the loan was used to build or improve the home. Medical and dental expenses have a higher threshold under AMT (15% of AGI instead of 7.5%), making them harder to deduct. Charitable contributions are allowed under both systems, but the calculation can differ.

Because so many deductions vanish, your AMTI is often much higher than your regular AGI, which is why AMT can kick in even for people who do not feel wealthy. A married couple in a high-tax state with a large mortgage and significant charitable giving can easily trigger AMT even at moderate income levels.

Income items that trigger AMT more often

Certain types of income make AMT more likely. Incentive stock options (ISOs) are a major trigger: the difference between the exercise price and the fair market value of the stock on the exercise date counts as AMT income, even if you have not sold the stock yet. This can create a large AMT bill in the year you exercise options, even if you have not received any cash.

Private activity bond interest — interest from municipal bonds issued for non-public purposes — is taxable under AMT but not under regular tax. Accelerated depreciation on real estate is also an AMT adjustment. If you have significant passive losses from rental property or other sources, those losses may be limited differently under AMT than under regular tax.

Exercising ISOs is the most common reason younger, higher-income taxpayers encounter AMT. If you receive options as part of your compensation, your tax professional should model the AMT impact before you exercise, because the tax bill can be substantial and arrive in the same year as the exercise, not when you sell the stock.

AMT credits and carryforwards

If you pay AMT in a given year, you may be able to use an AMT credit in future years to reduce your regular tax. The credit applies only to the AMT you paid on "deferral items" — adjustments that are temporary, like depreciation or timing differences. AMT paid on permanent adjustments, like the disallowance of SALT, does not generate a credit.

The AMT credit can be carried forward indefinitely, so you do not lose it if you cannot use it in the year you pay AMT. However, you can only use the credit in years when your regular tax exceeds your tentative AMT. If you pay AMT one year and then have lower income the next year, you may not be able to use the credit when ready.

This credit system is one reason it is important to track AMT payments over time. If you pay AMT because you exercised ISOs, you should expect to reclaim some of that tax through credits in future years when your income is lower or when you sell the stock and realize the gain.

State AMT and federal AMT differences

A handful of states — including California, Connecticut, Delaware, Florida, Illinois, Iowa, Kansas, Maine, Maryland, Minnesota, Mississippi, Missouri, Montana, New Hampshire, New Jersey, New York, Oklahoma, Oregon, Rhode Island, Tennessee, Vermont, and Virginia — have their own state-level AMT. The rules vary by state and do not always match the federal AMT.

California's AMT, for example, has lower exemption thresholds than the federal AMT, which means more California residents trigger state AMT even if they do not owe federal AMT. Some states have eliminated their AMT entirely in recent years. If you live in a state with AMT, you will need to file a separate state AMT calculation in addition to the federal one.

Your tax software or tax professional should handle both calculations, but it is worth confirming that they are calculating state AMT if you live in a state that has one. State AMT can add hundreds or thousands of dollars to your total tax bill, so it should not be overlooked.

Planning strategies when AMT is a concern

If you are close to the AMT threshold, timing certain deductions can help. Bunching charitable contributions into a single year, for example, can maximize their value in that year and potentially keep you below the AMT threshold in other years. Deferring income when possible — such as delaying the exercise of stock options to a year when you expect lower income — can also help.

If you receive incentive stock options, working with a tax professional to model different exercise scenarios is essential. Exercising a large number of options in a single year can trigger a substantial AMT bill, but spreading exercises across multiple years may allow you to stay below the threshold. Similarly, if you are selling appreciated stock, the timing of the sale can affect whether you owe AMT.

For real estate investors and business owners, understanding which deductions are allowed under AMT can inform decisions about depreciation methods and timing of expenses. These strategies require planning before the year ends, so discussing AMT with your tax professional in the fall, not after the year closes, gives you more options.

Frequently Asked Questions

Do I have to file Form 6251 if I think I might owe AMT?

You only file Form 6251 if you actually owe AMT. Most tax software calculates it automatically. If your income is below the AMT threshold for your filing status, you do not need to file it. If you are in the borderline range, your tax software will tell you whether you owe AMT.

Can I deduct state and local taxes under AMT?

No. State and local income taxes and property taxes are completely disallowed under AMT, even though you can deduct up to $10,000 of SALT on your regular return. This is one of the biggest reasons high-income earners in high-tax states trigger AMT.

What happens if I exercise stock options and owe AMT?

You will owe AMT in the year you exercise, based on the spread between the exercise price and the stock's fair market value. You may be able to reclaim some of this tax through AMT credits in future years, but the credit is limited and can take years to use. Model the impact before exercising large numbers of options.

If I paid AMT last year, will I owe it again this year?

Not necessarily. AMT depends on your income, deductions, and the types of income you receive in each specific year. A year with lower income, fewer deductions, or no stock option exercises may not trigger AMT even if you owed it the previous year.

Does my state have AMT?

About 20 states have their own AMT with different rules than federal AMT. If you live in one of these states, you will need to calculate state AMT separately. Your tax software or tax professional should handle this, but confirm that they are calculating it if you live in a state that has one.