AMT Risk on Incentive Stock Options: Who Gets Hit

Exercise 10,000 incentive stock options with a $40 spread between strike and fair market value, and you’ve just added $400,000 of phantom income to your alternative minimum taxable income — income you can’t spend, on shares you haven’t sold. For a married couple in California, that single non-cash event can trigger a federal AMT bill north of $90,000, due in April, payable in actual dollars. The shares might be worth nothing by then.

That gap — between paper value at exercise and cash owed at filing — is the entire AMT problem for ISO holders. The 2026 rules made it sharper. The One Big Beautiful Bill Act (OBBBA, P.L. 119-1), enacted July 2025, kept the higher exemption amounts permanent but cut the phaseout thresholds roughly in half and doubled the phaseout rate. More high earners with sizable spreads will owe AMT in 2026 than in 2025, even with identical exercises.

The key numbers at a glance

Source: IRS Rev. Proc. 2025-32 (2026); Rev. Proc. 2024-40 (2025); OBBBA §70105, §70107. Single-filer 2026 phaseout begins at $500,000.

How the ISO bargain element becomes a tax preference

An ISO produces no regular taxable income at grant or exercise. That’s the entire appeal — and the trap. Under the regular tax system, you exercise, you hold, and nothing happens until you sell. The AMT system disagrees.

When you exercise and hold ISOs past year-end, the spread between your strike price and the fair market value at exercise — the bargain element — becomes an AMT preference item. It gets added back to your income inside the parallel AMT calculation, even though you received no cash and sold nothing. A 10,000-share exercise at a $5 strike with a $45 FMV generates a $400,000 spread. Zero regular income. $400,000 of additional alternative minimum taxable income.

The mechanics run in five steps on IRS Form 6251. Start with regular taxable income. Add back the ISO bargain element and other preferences to reach AMTI. Subtract the exemption (which itself phases out at higher income). Apply 26% to taxable excess up to $244,500 and 28% above that for 2026. Compare the resulting tentative minimum tax against your regular tax — you owe the difference. The distinction between the spread at exercise and a later disqualifying disposition matters here, and those mechanics are unpacked in our ISO and NSO tax cost comparison.

What OBBBA changed, and why 2026 hits harder

The headline relief survived. OBBBA made the TCJA-era exemption amounts permanent and kept them inflation-indexed, so the $140,200 MFJ shield for 2026 isn’t going away. The damage is in the phaseout.

Two changes compound. First, the income level where the exemption begins to vanish dropped sharply — for married couples filing jointly, from $1,252,700 in 2025 to $1,000,000 in 2026. Second, the phaseout rate doubled, from 25 cents per dollar of AMTI above the threshold to 50 cents. Above the threshold, your exemption now erodes twice as fast, and it starts eroding $252,700 of income earlier.

Consider a married couple with $1.1 million of AMTI after an ISO exercise. In 2026 they sit $100,000 over the $1,000,000 threshold. At the 50% rate, that strips $50,000 off the $140,200 exemption, leaving roughly $90,200 of shield. Under 2025 rules — higher threshold, slower phaseout — the same couple would have kept their full exemption. The exercise didn’t change. The law did. This is the kind of year-boundary timing that turns a routine vest-and-hold decision into a six-figure swing, a theme that recurs across equity compensation tax planning.

Source: IRS Rev. Proc. 2025-32, Rev. Proc. 2024-40; OBBBA §70107. 2026 phaseout: 50% of AMTI over $1,000,000. 2025 phaseout: 25% of AMTI over $1,252,700. Exemption fully phased out at $1,280,400 (2026) and $1,800,700 (2025).

Who actually gets hit

The AMT is narrow by design. The Tax Policy Center estimates the number of AMT taxpayers fell to roughly 200,000 after TCJA, down from over five million in 2017. Most $150k+ households never see it in a normal year. ISO exercises are the exception that pulls otherwise-unaffected earners into the parallel system.

Three profiles carry real exposure. The first: an employee at a private company exercising and holding ISOs with a large spread, where the bargain element alone can dwarf salary. The second: a high earner in a high-tax state, where lost SALT deductions inside AMT stack on top of the ISO preference. The third, newly enlarged for 2026: couples between $1 million and $1.28 million of AMTI, who under the old phaseout kept most of their exemption and now watch it disappear.

Salary alone rarely triggers AMT — wages are taxed the same under both systems, so they don’t create a gap. What creates the gap is a large add-back the regular system ignores. The ISO bargain element is the cleanest example: a number that exists only inside Form 6251. The bigger the spread relative to your regular tax, the more likely tentative minimum tax exceeds regular tax, and the larger your check.

Modeling the cost: three ISO scenarios

The table below models exercise-and-hold for a married couple filing jointly in 2026, varying the spread and base income. Each assumes the couple holds past year-end (triggering the preference) and has no other major add-backs beyond SALT. Regular tax is estimated from 2026 ordinary brackets; AMT owed is the excess of tentative minimum tax over regular tax.

Illustrative model by Finluxy using IRS Rev. Proc. 2025-32 rates (26% to $244,500 taxable excess, 28% above; 50% exemption phaseout over $1,000,000 AMTI). AMT owed is tentative minimum tax minus estimated regular tax; figures rounded and exclude state tax, foreign tax credits, and other preferences. Actual liability requires full-return modeling on Form 6251.

Scenario C shows the 2026 trap in isolation. The higher base income pushes AMTI past $1 million, the phaseout strips $50,000 off the exemption, and the marginal cost of the same $600,000 spread climbs versus Scenario B despite identical option mechanics. The decision to exercise now versus stagger across tax years — explored in our vest, sell, or hold tax math — is where most of the controllable cost lives.

The Finluxy Equity After-Tax Yield on an ISO exercise-and-sale

AMT on a held ISO is a timing cost, not always a permanent one — you generally recover it later as a minimum tax credit if you eventually pay more regular tax than AMT. The cleaner yield comparison is the disqualifying disposition: exercise and sell in the same year. No AMT preference applies, but the entire spread becomes ordinary income, taxed at full marginal rates plus state and Medicare.

The Finluxy Equity After-Tax Yield measures net after-tax proceeds as a percentage of pre-tax fair market value at the event: (FMV − total taxes paid) ÷ FMV × 100. Modeled below for a $400,000 bargain element on a same-year disqualifying disposition, for a top-bracket couple, comparing a no-income-tax state against California.

Finluxy calculation. Federal top ordinary rate 37% (IRS, 2026 brackets); additional Medicare 0.9% on wage income over $250,000 MFJ (IRS); California top marginal rate 13.3% including 1% Behavioral Health Services surcharge over $1M (CA FTB / MHSA). Assumes spread is W-2 compensation already past the Social Security wage base; ignores deductions. Same-year sale, so no AMT preference.

A California couple keeps under half of an ISO disqualifying disposition’s pre-tax value — a 48.8% yield that mirrors what equity holders see on RSU vests in the same state. If they instead held for the qualifying period (two years from grant, one from exercise), the gain converts to long-term capital gains and the yield rises substantially, but they take AMT risk in the exercise year and market risk on the shares. That trade — AMT timing cost and concentration risk now, versus a higher yield later — is the core ISO decision. Whether the qualifying hold pays off depends on the same logic as an 83(b) election’s tax gamble: you accept a tax cost today to start a capital gains clock, betting the shares hold value.

What most coverage overlooks

The standard ISO warning fixates on the exercise spread. The 2026 dataset shows the bigger 2026 swing comes from the phaseout cliff between $1 million and $1.28 million of AMTI, where the doubled phaseout rate erases the exemption entirely. A couple at $1.28 million of AMTI in 2026 has zero exemption; the same couple in 2025 still held $130,175 of shield. That $140,200 difference, taxed at 26–28%, is roughly $36,000 to $39,000 of additional AMT created purely by the law change — independent of how large the ISO spread is.

Put differently: in 2026, base income now amplifies ISO AMT cost in a way it didn’t in 2025. A high salary that pushes AMTI over $1 million doesn’t just add ordinary tax — it strips the exemption that would have softened the ISO preference. Most ISO commentary still treats salary and the bargain element as separate problems. Under the new phaseout, they interact, and the interaction is where the surprise bills come from.

Methodology

What this means for a $150k+ household

At $150k of household income with no equity event, AMT is almost certainly irrelevant — the exemption covers you comfortably. The exposure switches on with the exercise. A single-year ISO exercise with a large spread is the most common way a $150k–$400k household lands on Form 6251, and the cost is fully a function of timing you control.

Three thresholds deserve a place in any exercise decision. The 26%/28% breakpoint at $244,500 of taxable excess sets the marginal AMT rate on the spread. The $1,000,000 AMTI phaseout (MFJ; $500,000 single) determines whether your exemption survives — and crossing it in 2026 is far costlier than it was in 2025. And the qualifying holding period — two years from grant, one from exercise — decides whether your eventual sale is taxed as long-term capital gain or as ordinary income at rates that, in California, leave under half the value. Households near the $1 million AMTI line have the most to gain from spreading exercises across tax years to stay under the phaseout, or from modeling a partial exercise that keeps AMTI below the cliff. The minimum tax credit recovers AMT over time only if you later pay more in regular tax, so for someone planning to leave a high-tax state or expecting lower future income, the credit may not come back cleanly — which makes the year-of-exercise cost closer to permanent than the “it’s just timing” framing suggests. Running the numbers on Form 6251 before exercising, ideally with a preparer who models multiple exercise years, is the difference between a planned cost and an April surprise.