Updated October 7, 2026. Quick answer: Form 6251 figures the alternative minimum tax, a separate tax imposed in addition to regular tax. Part I adds adjustments and preferences to taxable income to reach AMTI, Part II subtracts an exemption of $88,100 for single filers or $137,000 for joint filers in 2025, and applies 26% up to $239,100 and 28% above it. Exercising incentive stock options is one of the common line 2i adjustments. Tax paid can come back later as a credit on Form 8801.
More IRS forms and schedules for individual filers, read line by line: Form 8911 instructions and Form 3800 instructions.
More IRS forms and schedules, read line by line: Form 8801 instructions.
Foreign tax credit (Form 1116) and alternative minimum tax (Form 6251) for 2025, read line by line: Form 6251 line 1, Form 6251 line 2a and Form 6251 line 2l.
Schedule 3 (Form 1040) for 2025, read line by line: Schedule 3 lines 6a to 6e.
Schedule 2 (Form 1040) for 2025, read line by line: Schedule 2 lines 2 and 3.
The shareholder’s Schedule K-1 (Form 1120-S), boxes 13 to 19: Schedule K-1 boxes 14 and 15.
The partner’s Schedule K-1 (Form 1065), read box by box: Schedule K-1 box 17 and Schedule K-1 box 21.
The partner’s Schedule K-1 (Form 1065), read box by box: Schedule K-1 box 6 and Schedule K-1 box 9.
More IRS forms and schedules, read line by line: Schedule 2 instructions.
More IRS forms and schedules, read line by line: Form 4952 instructions.
What the AMT is and who files Form 6251
“Use Form 6251 to figure the amount, if any, of your alternative minimum tax (AMT). The AMT is a separate tax that is imposed in addition to your regular tax.” The IRS explains why it exists: “The AMT sets a limit on the amount these benefits can be used to reduce total tax.”
The first filing test is simple: “Form 6251, line 7, is greater than line 10.” The other three tests involve credits and negative adjustments on lines 2c through 3. One test reads “You claim the qualified electric vehicle credit (Form 8834), the personal-use part of the alternative fuel vehicle refueling property credit (Form 8911), or the credit for prior year minimum tax (Form 8801).”
2025 exemption amounts and the phaseout
The instructions open with the changed figures: “The exemption amount on Form 6251, line 5, has increased to $88,100 ($137,000 if married filing jointly or qualifying surviving spouse; $68,500 if married filing separately).”
They add: “the amount used to determine the phaseout of your exemption has increased to $626,350 ($1,252,700 if married filing jointly or qualifying surviving spouse).”
| Filing status | Exemption (line 5) | Phaseout begins above | Exemption is zero at |
|---|---|---|---|
| Single or head of household | $88,100 | $626,350 | $978,750 |
| Married filing jointly or qualifying surviving spouse | $137,000 | $1,252,700 | $1,800,700 |
| Married filing separately | $68,500 | $626,350 | $900,350 |
The last column comes from the Exemption Worksheet note, which says the exemption is zero when line 4 is “equal to or more than $978,750 if single or head of household, $1,800,700 if married filing jointly or qualifying surviving spouse, or $900,350 if married filing separately”.
Worked example: the Exemption Worksheet
The worksheet takes the base exemption, subtracts 25% of AMTI above the phaseout threshold, and floors the result at zero. In this computed illustration, take a single filer with AMTI of $700,000 on line 4. The excess over $626,350 is $73,650. Multiplying by 25% gives $18,412.50. The exemption on line 5 is $88,100 minus $18,412.50, which is computed as $69,687.50. The arithmetic is worked here from the printed worksheet steps; the IRS does not print this example.
The worksheet’s own steps: “Subtract line 3 from line 2. If zero or less, enter -0-” then “Multiply line 4 by 25% (0.25)” then “Subtract line 5 from line 1. If zero or less, enter -0-.” For the year-specific limits in other tax years, see the 2026 AMT exemption page and the 2027 page.
Part I: the adjustments on lines 2a to 3
Part I starts from taxable income and adds items taxed differently under the AMT. Line 2a is the first: “Enter the amount of all taxes from Schedule A (Form 1040), line 7, except any generation-skipping transfer taxes on income distributions.” Without Schedule A the standard deduction amount goes there instead. The standard deduction matters in a second way: “the standard deduction isn’t allowed for the AMT”.
| Line | What it captures |
|---|---|
| 2a | Taxes from Schedule A line 7, or the standard deduction |
| 2b | Refunds of state or local taxes, entered as a negative |
| 2c | Investment interest, difference between regular tax and AMT |
| 2g | Interest from specified private activity bonds |
| 2h | Qualified small business stock, 7% of the excluded gain |
| 2i | Exercise of incentive stock options |
| 2k to 2n | Disposition of property, depreciation, passive activities, loss limitations |
Private activity bonds are covered by “Each payer of this type of interest should send you a Form 1099-INT showing the amount of this interest in box 9.” Line 4 then combines lines 1b through 3 into AMTI.
Incentive stock options on line 2i
The ISO rule is the one most employees meet. “For the regular tax, no income is recognized when an incentive stock option (ISO), as defined in section 422(b), is exercised. However, this rule doesn’t apply for the AMT.”
The IRS example uses a Form 3921 with $10 in box 3, $25 in box 4 and 100 shares in box 5. The FMV of all the shares is $2,500 and the amount paid is $1,000, and the IRS says “Your adjustment is $1,500”. Two related rules matter. Selling in the same year removes the adjustment: “If you acquired stock by exercising an ISO and you disposed of that stock in the same year, the tax treatment under the regular tax and the AMT is the same, and no adjustment is required.” And the basis rises: “Increase your AMT basis in any stock acquired through the exercise of an ISO by the amount of the adjustment.”
See the ISO bargain element calculator and the disqualifying disposition page.
Part II: the 26% and 28% rates, and Part III
For the 2025 return: “the 26% tax rate applies to the first $239,100 ($119,550 if married filing separately) of taxable excess (the amount on line 6).” Line 7 on the form reads “Otherwise, multiply line 6 by 28% (0.28) and subtract $4,782 ($2,391 if married filing separately) from the result.”
The subtraction keeps the two rates continuous. Computed here, at the $239,100 breakpoint 26% is $62,166 and 28% is $66,948. Subtracting $4,782 from $66,948 leaves $62,166 again. These products are computed here.
Filers with capital gain distributions, qualified dividends, or a gain on both Schedule D lines 15 and 16 complete Part III instead: “complete Part III on the back and enter the amount from line 40 here.” Part III applies the maximum capital gains rates to the AMT.
The credit for prior year minimum tax
Form 8801 is the next step: “if you paid AMT for 2024 or you had a minimum tax credit carryforward on your 2024 Form 8801.” The forward-looking sentence is: “If you pay AMT for 2025, you may be able to take a credit on Form 8801 for 2026.” Recovery is covered on the AMT credit page.
Which revision applies
The edition read for this page is the 2025 Form 6251 and its instructions, dated Jan 8, 2026, which were the revision irs.gov served when they were read on 2026-10-07 and which apply to returns filed in 2026. A later revision can change the amounts, so check the form in use. “For the latest information about developments related to Form 6251 and its instructions, such as legislation enacted after they were published, go to IRS.gov/Form6251.”
Every Form 6251 line and part page in one table
Each row links to the page that reads a line, group of lines or part of Form 6251. The right column is the summary each page carries.
| Page | What it covers |
|---|---|
| Form 6251 Line 1: Starting Income (2025 Return) | What goes on Form 6251 lines 1a and 1b for 2025: the two subtractions that start the alternative minimum taxable income and where each number comes from. |
| Form 6251 Lines 2a to 2c: Taxes, Refunds, Interest (2025) | What goes on Form 6251 lines 2a, 2b and 2c for 2025: taxes from Schedule A, state tax refunds as a negative, and the AMT investment interest difference. |
| Form 6251 Lines 2d to 2h: Depletion, NOL, Bonds, QSBS | What goes on Form 6251 lines 2d to 2h for 2025: depletion, the net operating loss lines, private activity bond interest and qualified small business stock. |
| Form 6251 Line 2i: Incentive Stock Options (2025 Return) | What goes on Form 6251 line 2i for 2025: the excess of the stock’s value over what you paid when you exercise an incentive stock option. |
| Form 6251 Line 2k: Disposition of Property (2025 Return) | What goes on Form 6251 line 2k for 2025: the AMT difference in gain or loss from Forms 4797, 4684, 8949 and Schedule D, and when it is negative. |
| Form 6251 Line 2l: Post-1986 Depreciation (2025 Return) | What goes on Form 6251 line 2l for 2025: the AMT difference on depreciation for property placed in service after 1986, and which property is left out. |
| Form 6251 Lines 2m to 2t: Passive and Cost Adjustments (2025) | Form 6251 lines 2m to 2t on the 2025 return: passive activities, loss limits, and the cost adjustments each line asks for, in the IRS’s words. |
| Form 6251 Lines 3 and 4: Other Adjustments and AMTI (2025) | Form 6251 lines 3 and 4 on the 2025 return: what other adjustments go on line 3 and how line 4 totals alternative minimum taxable income. |
| Form 6251 Lines 5 to 7: Exemption and AMT Base (2025 Return) | Form 6251 lines 5 to 7 on the 2025 return: the exemption, the subtraction on line 6 and how line 7 is figured, including Part III and Form 2555 filers. |
| Form 6251 Lines 8 to 11: AMT Foreign Tax Credit and AMT | Form 6251 lines 8 to 11 on the 2025 return: the AMT foreign tax credit, tentative minimum tax, the regular tax on line 10 and the AMT on line 11. |
| Form 6251 Part III Lines 12 to 40: Capital Gains Rates (2025) | Form 6251 Part III on the 2025 return: who completes lines 12 to 40, what lines 13 to 15 pull from your worksheets, and how line 40 returns to line 7. |
Common mistakes
- Using the full exemption without checking AMTI against the phaseout threshold. Above $626,350 for single filers the Exemption Worksheet reduces it by 25% of the excess.
- Skipping the ISO adjustment because no stock was sold. Line 2i applies on exercise unless the stock is disposed of in the same year.
- Assuming the standard deduction carries over. It is not allowed for the AMT, so line 2a adds it back when Schedule A is not filed.
Related: AMT exemption 2026, ISO AMT bargain element calculator, AMT credit recovery, and NSO vs ISO tax.
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- Instructions for Form 6251 (2025): https://www.irs.gov/pub/irs-pdf/i6251.pdf
- Form 6251 (2025): https://www.irs.gov/pub/irs-pdf/f6251.pdf
Read from the IRS documents linked above on October 7, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.