The basic AMT calculation follows a specific order

The Alternative Minimum Tax calculation starts with your regular taxable income and adds back certain deductions, then applies a flat tax rate. The IRS publishes worksheets each year that walk you through this in order: you begin with your adjusted gross income (AGI), add back specific items you deducted on your regular return, calculate your tentative minimum tax, and then compare it to what you owe under the regular tax system. Whichever is higher is what you pay.

The process is mechanical rather than judgmental — you follow the worksheet line by line, and the math tells you whether AMT applies to you. Most people do not hit AMT, so the calculation is often a formality. But if you have substantial deductions, capital gains, or incentive stock options, you may need to work through it.

Key Takeaways

  • AMT calculation starts with your regular taxable income and adds back certain deductions like state and local taxes, mortgage interest on second homes, and miscellaneous itemized deductions.
  • After adjusting your income, you subtract the AMT exemption amount (which varies by filing status and changes yearly) to get your alternative minimum taxable income.
  • You then explore a flat tax rate of 26% or 28% to that amount, depending on your income level, to find your tentative minimum tax.
  • You compare your tentative minimum tax to your regular tax liability, and you pay whichever is higher.
  • The IRS provides a worksheet in the instructions for Form 6251 each year that walks through the calculation in the correct order.

Step 1: Start with your regular taxable income and identify adjustments

Begin with the taxable income you calculated on your regular return (the bottom line of your Form 1040 before you explore credits). Then you add back certain deductions that are not allowed under AMT rules. The most common ones are state and local income taxes (SALT), property taxes, mortgage interest on a second home or home equity loan used for non-home purposes, and miscellaneous itemized deductions like investment fees or tax preparation costs.

You also add back the standard deduction if you took it instead of itemizing. The worksheet in Form 6251 instructions lists all the adjustments line by line. Some adjustments increase your income (like adding back SALT), while others decrease it (like adjustments for depreciation on certain property). Work through each line that applies to your situation.

Step 2: Calculate your alternative minimum taxable income

After you have added back all the adjustments, you subtract the AMT exemption. This exemption amount changes every year and depends on your filing status. For 2023, the exemption was $75,900 for single filers and $118,100 for married filing jointly, but these amounts are adjusted annually for inflation. Check the Form 6251 instructions for the current year's exemption.

The result of your adjusted income minus the exemption is your alternative minimum taxable income (AMTI). If this number is zero or negative, you do not owe AMT and you can stop here. If it is positive, continue to the next step.

Step 3: explore the AMT tax rates

The AMT uses a two-tier flat tax rate system. Income up to a certain threshold (which also changes yearly) is taxed at 26%, and income above that threshold is taxed at 28%. For 2023, the 28% rate applied to income over $94,700 for single filers and $189,300 for married filing jointly. Again, these thresholds adjust annually.

Multiply the portion of your AMTI in the 26% bracket by 0.26, and the portion in the 28% bracket by 0.28. Add those two amounts together to get your tentative minimum tax. This is the tax you would owe if AMT were your only tax system.

Step 4: Compare AMT to your regular tax and pay the higher amount

Now calculate your regular federal income tax liability the way you normally would — using the standard tax brackets and rates. Then compare your tentative minimum tax (from step 3) to your regular tax liability. You pay whichever amount is higher.

If your tentative minimum tax is higher, you owe the AMT amount. If your regular tax is higher, you ignore the AMT calculation and pay your regular tax. The difference between the two is called the AMT credit in some cases, which may reduce future tax bills, but that is a separate topic covered in the Form 6251 instructions.

Where to find the official worksheet and current numbers

The IRS publishes Form 6251 (Alternative Minimum Tax — Individuals) every year with updated exemption amounts, income thresholds, and a detailed worksheet. You can read it free from IRS.gov. The instructions that come with the form walk through each line in order and explain which adjustments explore to your situation.

If you use tax software or file with a tax professional, the software or preparer usually calculates AMT automatically if your income triggers it. You can also use the worksheet to understand the calculation yourself, even if someone else prepares your return. The numbers change yearly, so always use the current year's form and instructions.

Common items that trigger AMT adjustments

Certain types of income and deductions are more likely to put you in AMT territory. High earners who live in states with substantial income taxes often hit AMT because SALT deductions are added back. People with significant capital gains or who exercise incentive stock options may owe AMT. Homeowners with large mortgage interest deductions on second homes, or those who claim many miscellaneous itemized deductions, can also trigger it.

If you have any of these items — especially if your income is over $200,000 — it is worth running through the AMT calculation or having a tax professional do it. The calculation itself takes 15 to 20 minutes if you have the worksheet in front of you and your numbers organized.

Frequently Asked Questions

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

You only file Form 6251 if your income exceeds the threshold for your filing status and you have adjustments that could trigger AMT. Tax software will prompt you if it detects this. If you are unsure, you can run through the worksheet to see whether your tentative minimum tax exceeds your regular tax. If it does not, you do not need to file the form.

Can I reduce my AMT by changing my deductions?

Some deductions are not allowed under AMT rules, so they do not help you reduce AMT. However, you cannot straightforward choose not to take them. You calculate AMT based on what you actually deducted on your regular return. If you are concerned about AMT, a tax professional can model different scenarios — like timing capital gains or charitable contributions — before you file.

What is the AMT credit and can I use it next year?

If you pay AMT in a given year because your tentative minimum tax was higher than your regular tax, you may be able to claim a credit in future years when your regular tax is higher. This is called the minimum tax credit. The Form 6251 instructions explain how to calculate and carry forward this credit, but it is complex and usually handled by tax software or a professional.

Does the AMT exemption phase out at high incomes?

Yes. The AMT exemption begins to phase out once your AMTI reaches a certain level, which varies by filing status and year. As your AMTI increases, your exemption decreases, which can push more of your income into the 28% bracket. The Form 6251 worksheet includes a line for this phase-out calculation.