Alternative Minimum Tax: Model It Before the Transaction
AMT is a second tax calculation, not a second tax bracket. The expensive surprises usually come from incentive stock options and year-end decisions made without running both systems.
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Quick Answer
The alternative minimum tax (AMT) is a parallel federal tax calculation. Form 6251 rebuilds taxable income under AMT rules, subtracts the AMT exemption, calculates tentative minimum tax, and compares it with regular tax. You pay the difference only when the AMT result is higher. For 2026, the exemption is $90,100 for single filers and $140,200 for married couples filing jointly, with phaseouts beginning at $500,000 and $1,000,000 respectively.
How the Alternative Minimum Tax Works
One return, two calculations, one comparison
AMT does not replace the regular tax system. It runs beside it. The regular return allows one set of deductions and timing rules; Form 6251 changes selected items and computes a tentative minimum tax. If that tentative amount exceeds regular tax, the excess becomes AMT on Schedule 2.
| Step | What happens |
|---|---|
| 1. Start with regular taxable income | Use the income and deductions already computed for the regular federal return. |
| 2. Recalculate under AMT rules | Add or subtract Form 6251 adjustments and preference items to arrive at alternative minimum taxable income (AMTI). |
| 3. Apply the exemption and AMT rates | Subtract the allowed exemption, then apply 26% and 28% rates, with separate capital-gain-rate mechanics when applicable. |
| 4. Compare the systems | If tentative minimum tax exceeds regular tax, the difference is AMT. |
The rate is rarely the real issue
AMT uses only two ordinary rates, but it can tax a much larger base. A large ISO bargain element can enter AMTI without producing sale proceeds, while deductions that lowered regular taxable income may disappear in the AMT calculation.
2026 AMT Exemption and Phaseout
Current figures verified against IRS Rev. Proc. 2025-32
| Filing status | 2026 exemption | Phaseout begins |
|---|---|---|
| Single or head of household | $90,100 | $500,000 |
| Married filing jointly or surviving spouse | $140,200 | $1,000,000 |
| Married filing separately | $70,100 | $500,000 |
The exemption is reduced by 25 cents for each dollar of AMTI above the phaseout threshold. After the exemption, the 26% rate applies through $244,500 of AMT taxable excess for most filers in 2026, and 28% applies above that amount. For married filing separately, the 28% threshold is $122,250. Preferential rates for qualified dividends and long-term capital gains still require a separate computation.
Do not compare gross income with the exemption
The exemption applies to AMTI after Form 6251 adjustments, not to salary, AGI, or regular taxable income by itself. A filer below a phaseout threshold can still owe AMT, and a high-income filer can avoid it if regular tax remains higher.
The AMT Triggers That Matter
Transactions and deductions that make the two systems diverge
- Incentive stock options. Exercising and holding ISOs can add the bargain element to AMTI before the stock produces cash.
- State and local taxes. Taxes deducted on Schedule A for regular tax are not deductible in computing AMTI.
- Certain private activity bond interest. Interest that is tax-exempt for regular tax can be an AMT preference item.
- Depreciation and passive-activity differences. Business and investment assets can produce different timing under the two systems.
- Large income events. A conversion, sale, bonus, or business-income spike can shrink the exemption and change whether other adjustments produce AMT.
ISO Exercise Example
How a paper gain creates a real cash requirement
| ISO shares exercised | 10,000 |
| Exercise price | $10 per share |
| Fair market value at exercise | $35 per share |
| Cash paid to exercise | $100,000 |
| Bargain element added for AMT | $250,000 |
| Sale proceeds in the exercise year | $0 if the shares are held |
The AMT adjustment is 10,000 shares multiplied by the $25 spread at exercise: $250,000. The exact AMT is not $250,000 multiplied by a single rate; it depends on the rest of the return, the exemption phaseout, regular tax, and capital-gain items. The key cash-flow problem is simpler: the taxpayer has already paid $100,000 for illiquid shares and may owe tax without selling any.
Exercise size should follow a tax-and-liquidity model
Model several exercise blocks, the share price at exercise, the cash reserve for tax, and the downside if the stock falls after December 31. A smaller staged exercise can preserve more flexibility than a single all-in exercise.
Form 6251 and Planning Decisions
Use the form as a model, not an April surprise
- 01Build a full-year baseline. Project regular taxable income, credits, withholding, estimates, and known AMT adjustments.
- 02Model the transaction in blocks. For ISOs, compare several exercise quantities and prices instead of asking only whether to exercise all or none.
- 03Separate tax cost from cash risk. Include the exercise price, estimated AMT, liquidity window, and downside scenario in the same decision.
- 04Re-run before year-end. Actual compensation, deductions, and share value will change. Refresh the model before another exercise or sale.
- 05Track basis in both systems. ISO shares can carry a regular basis and a different AMT basis. Preserve exercise confirmations and prior Forms 6251 and 8801.
Start with the 2026 tax brackets and calculator for regular-tax context, then coordinate withholding or estimated tax payments with the AMT projection. The bracket tool alone does not calculate AMT.
AMT Credit Recovery
Form 8801 distinguishes temporary differences from permanent ones
AMT adjustments fall into two broad groups. Deferral items change timing but generally do not create a permanent income difference; the ISO adjustment is the planning example most high-income employees encounter. Exclusion items, including certain itemized deductions, create a permanent difference.
Form 8801 calculates the minimum tax credit attributable to deferral items and any carryforward. The credit is limited in a later year by the relationship between regular tax and tentative minimum tax. That is why “you get the AMT back” is too strong: a credit may exist, but the amount usable each year depends on future returns.
Keep a credit schedule beside the ISO lot schedule
Track regular basis, AMT basis, exercise dates, dispositions, prior-year Form 6251 adjustments, Form 8801 credit generated, credit used, and remaining carryforward. Without that history, later recovery and sale reporting become unnecessarily expensive.
Alternative Minimum Tax FAQ
The planning questions behind Form 6251
Primary sources
Continue the equity-compensation plan
Model the Exercise Before the Share Price Sets the Tax
Taxstra models regular tax, AMT, ISO lots, cash needs, and future credit recovery together. Book a free initial consultation before the exercise or year-end deadline.