What this line means
The alternative minimum tax (AMT) calculated on Form 6251. The AMT is a parallel tax system that recalculates your tax liability by adding back certain deductions — most commonly state and local tax deductions, certain interest deductions, and incentive stock option exercises. If the AMT calculation produces a higher tax than your regular tax, the difference goes here.
Does this apply to you?
- You claimed large state and local tax deductions on Schedule A
- You exercised incentive stock options (ISOs) during the year
- You have significant tax-exempt interest from private activity bonds
- You claimed accelerated depreciation on business or rental property
- Your income exceeds approximately $200,000 and you itemize deductions
Easy to overlook
The AMT exemption shields most filers For 2025, the AMT exemption is $88,100 for single filers and $137,000 for married filing jointly. 1 Your AMT taxable income must exceed these amounts before the AMT kicks in. The exemption phases out at higher incomes — starting at $626,350 for single filers and $1,252,700 for married filing jointly — but most middle-income filers are fully protected by the exemption. You still must complete Form 6251 to verify you do not owe AMT, even if the result is zero. IRS Form 6251 Instructions — Alternative Minimum Tax
Exercising incentive stock options is the most common AMT trigger for high-income earners When you exercise an ISO, the difference between the exercise price and the fair market value (the “bargain element”) is not taxed as regular income — but it is added to your AMT income. 2 A tech employee who exercises $200,000 worth of ISOs at a $50,000 exercise price adds $150,000 to AMT income in one year. This catches employees by surprise because they owe AMT despite not selling the shares or receiving cash. General filing pattern — AMT triggered by large state tax deductions
Watch out for this
Assuming you do not owe AMT because you have never owed it before. The AMT is event-driven — it often appears in a single year when you exercise ISOs, realize a large capital gain, or move to a high-tax state. Tax software flags this automatically, but paper filers who skip Form 6251 because they “never had to fill it out” can miss a four- or five-figure tax liability.
Footnotes
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IRS Form 6251 Instructions, AMT Exemption Amount. https://www.irs.gov/instructions/i6251 ↩
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IRS Form 6251 Instructions, Incentive Stock Options. https://www.irs.gov/instructions/i6251 ↩