Alternative Minimum Tax 2026: AMT Exemption, Phaseout, Form 6251

The alternative minimum tax is not a separate tax system for exotic shelters anymore. For many individual taxpayers, the modern AMT shows up through two ordinary facts: a large incentive stock option exercise or deductions that count for regular tax but not for AMT. The calculation still runs through Form 6251, and the 2026 exemption numbers come from Revenue Procedure 2025-32.

What AMT Actually Does

The AMT starts with regular taxable income and rebuilds it under a different rulebook. Some deductions are added back. Some income that regular tax ignores for now is included. The result is alternative minimum taxable income, usually shortened to AMTI. From AMTI you subtract the AMT exemption, apply the AMT rates, and compare tentative minimum tax with regular tax. If tentative minimum tax is higher, the difference is AMT.

The IRS 2025 Instructions for Form 6251 were the latest full instructions available at review time in May 2026. Those instructions describe the purpose of the form: figuring whether you owe AMT, a separate tax imposed in addition to regular tax, when certain tax benefits significantly reduce regular tax. The 2026 exemption and phaseout figures below come from Rev. Proc. 2025-32, not from the 2025 form instructions.

2026 AMT Exemptions and Phaseouts

The phaseout rate is effectively 25 cents of exemption lost for each dollar of AMTI above the threshold. For a single filer with AMTI of $540,000, the excess over the $500,000 threshold is $40,000, so the exemption is reduced by $10,000. The $90,100 exemption becomes $80,100. Once AMTI reaches the complete phaseout amount, the exemption is gone.

Rev. Proc. 2025-32 also gives the 2026 AMT rate breakpoints. The 28% AMT rate applies to excess taxable income above $244,500 for all taxpayers except married filing separately; the married-filing-separately breakpoint is $122,250. Below those breakpoints, the AMT rate is 26%. Capital gains and qualified dividends can still receive preferential rate treatment inside the AMT calculation, which is one reason Form 6251 can be more complicated than the two-rate summary suggests.

The Big 2026 Triggers

The most visible AMT trigger for employees at private companies is the incentive stock option. The Form 6251 instructions say that for regular tax, no income is recognized when an ISO is exercised, but that rule generally does not apply for AMT. Instead, line 2i includes the excess of the fair market value of the stock over the amount paid for the stock, unless the shares are sold in the same year and the regular and AMT treatment line up.

State and local taxes are another recurring item. Under Form 6251, certain taxes deducted for regular tax are not allowed for AMT and are added back. That is why high-income taxpayers in high-tax states can see AMT pressure even without stock options, although the larger post-2017 AMT exemptions made this less common for many households. Private activity bond interest, depreciation differences, passive activity adjustments, and basis differences can also matter.

Worked Example: Sofia Exercises ISOs

Sofia is single and works for a late-stage software company. In 2026 she exercises 20,000 incentive stock options at a $5 strike price when the fair market value is $22. She does not sell the shares before year-end. The AMT adjustment is the bargain element: 20,000 × ($22 − $5) = $340,000. Her regular taxable income before AMT adjustments is $240,000, and her regular return includes a $10,000 state and local tax deduction that must be added back for AMT.

Her rough AMTI is therefore $240,000 + $340,000 + $10,000 = $590,000. Because she is single, the 2026 exemption starts at $90,100 and begins to phase out above $500,000. Sofia is $90,000 over the threshold, so she loses 25% × $90,000 = $22,500 of exemption. Her allowed exemption is $67,600. Her AMT taxable excess is $590,000 − $67,600 = $522,400.

Using the 2026 AMT rate breakpoint for an unmarried taxpayer, the first $244,500 of taxable excess is taxed at 26%, or $63,570. The remaining $277,900 is taxed at 28%, or $77,812. Tentative minimum tax is about $141,382 before credits. If Sofia's regular tax is $68,000, the rough AMT is $73,382. This is a simplified screen; actual Form 6251 may change the result through capital gain worksheets, credits, prior-year AMT credit, and other lines.

Worked Example: Ben and Jules Avoid AMT

Ben and Jules file jointly. Their 2026 AMTI is $230,000 after adding back a modest state tax deduction. Their joint exemption is $140,200 and does not phase out because their AMTI is below $1,000,000. Their taxable excess is $230,000 − $140,200 = $89,800. At 26%, tentative minimum tax is $23,348. If their regular tax is $31,000, they owe no AMT because regular tax is already higher than tentative minimum tax.

This example shows why AMT is not triggered merely by having a preference item. AMT is a comparison. A household can have an addback and still owe no AMT if the exemption and regular tax absorb it. Conversely, an ISO exercise can be large enough to create AMT even when the regular tax return looks ordinary.

ISO Planning Before Exercise

For ISOs, the key planning variable is the spread on the exercise date. A smaller spread means a smaller AMT adjustment. Exercising early in the year gives more time to watch the stock and potentially sell before year-end if the AMT cost becomes unacceptable, but selling too soon can create a disqualifying disposition for regular tax. Exercising late in the year gives less time for a same-year exit. Neither timing rule is universally better; the right answer depends on liquidity, concentration risk, expected valuation, and cash available for tax.

Ask for a current 409A or fair-market-value notice before exercise. Keep Form 3921. Track regular basis and AMT basis separately. If you pay AMT because of an ISO exercise and later sell the stock, you may have an AMT credit or a different AMT gain calculation. That is a place for careful software or a tax professional, not a napkin calculation.

Payroll and Withholding Angle

AMT surprises often happen because withholding is based on regular payroll wages, not on a taxpayer's full AMT exposure from ISOs, private activity bonds, or large addbacks. A W-2 employee can increase withholding on Form W-4, and a self-employed taxpayer can use estimated payments. If you receive a large equity grant or exercise options, run a mid-year projection. For business owners also managing payroll, the employer cost calculator and quarterly estimated tax guide can help separate payroll taxes from income-tax payment planning.

A Practical AMT Screening Routine

A quick screen will not replace Form 6251, but it catches the expensive surprises early. Start with projected taxable income. Add the items you already know are AMT-sensitive: ISO spread if shares will be held past year-end, state and local taxes deducted for regular tax, private activity bond interest, and any depreciation or basis differences your tax software tracked from prior years. Subtract the 2026 exemption for your filing status, then reduce that exemption if AMTI is above the phaseout threshold. Apply 26% and 28% to the excess using the Rev. Proc. 2025-32 breakpoint, then compare the result with projected regular tax.

If tentative minimum tax is only slightly above regular tax, withholding or an estimated payment may solve the cash-flow problem. If the gap is large, the planning choices are more substantive: exercise fewer ISO shares, sell enough shares in the same year to change the tax result, delay an exercise, or avoid stacking several AMT preference items into one year. The point is to make the decision while you still control the transaction.

Common Mistakes

• Assuming no sale means no tax. ISO exercise-and-hold can create AMT without cash proceeds.
• Using 2025 AMT exemptions for 2026 planning. The 2026 amounts are $90,100 single and $140,200 joint under Rev. Proc. 2025-32.
• Forgetting phaseout. High AMTI can reduce or eliminate the exemption, raising the effective AMT cost.
• Ignoring state AMT or state tax treatment. Some states have separate AMT or ISO rules. Federal Form 6251 is not the whole state answer.
• Failing to track AMT basis. ISO shares acquired in an AMT year can have a different basis for AMT than for regular tax.

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