AMT after the SALT cap: a worked example for ISO exercise.

The AMT — Alternative Minimum Tax — is the parallel tax system that catches startup employees who exercise Incentive Stock Options before a liquidity event. Most tech employees first hear about it the year after they exercised, when their CPA calls with a question that starts "so, about that ISO exercise…" and ends with a bill for tens of thousands of dollars they didn't expect.

This post is the worked example you should have read before exercising. We'll walk through one clean scenario — $400K W-2, 10K ISOs at $4 strike with $52 FMV, single filer — and show exactly where the AMT bite comes from. Then we'll cover the AMT credit (which is real and recoverable, often), the disqualifying-disposition trap that turns ISOs into NSOs, and how the post-2017-TCJA SALT cap interacts with it.

How AMT works in 90 seconds

The AMT is a parallel calculation. You compute your "regular" federal tax. You compute your AMT — which uses different rules: fewer deductions, different exemption, certain "preference items" added back. You pay whichever is higher.

For most W-2 earners, regular tax is higher than AMT, so AMT doesn't matter. Two situations flip that:

1. You exercise ISOs and hold past calendar year-end. The "bargain element" — FMV minus strike, times shares — gets added to AMT income but not to regular income. AMT income spikes. Regular tax doesn't. AMT > regular. You owe the difference.
2. Large state-tax + property-tax deductions getting capped. The 2017 Tax Cuts and Jobs Act capped state-and-local-tax deductions at $10K for regular tax purposes — which mostly closed the historical AMT-vs-regular gap that high-state-tax filers used to see. The SALT cap is scheduled to sunset after 2025 unless Congress extends it; if it sunsets, AMT becomes a bigger factor again for CA/NY/NJ residents in 2026 forward.

The worked example

Single filer, California resident. W-2 wages $400K. No other income. Exercises 10,000 ISOs at $4 strike when FMV is $52. Holds the shares past December 31. We'll use 2026 AMT rates (the 2026 AMT exemption for single filers is approximately $88,100, with phase-out starting at $639,300 — these figures get inflation-adjusted annually so confirm with your CPA before using these numbers in your own planning).

The exercise itself cost $40,000 in cash (10,000 × $4 strike). The AMT bite adds another ~$130K. The total cash outlay to exercise + hold is approximately $170,000 — for shares that may or may not be liquid for years.

The AMT credit — the recoverable part

The AMT you pay on ISO bargain elements isn't permanently lost. It generates an AMT credit (Form 8801) that you can use to reduce your regular tax in future years — specifically, in years when your regular tax exceeds your AMT. For most operators with one ISO exercise event, the AMT credit gets fully consumed over the 3–7 years following exercise as their regular tax recovers and they can claim back the credit against ordinary income.

The credit is non-refundable in any single year (you can only use it to reduce regular tax to your AMT level), but it carries forward indefinitely until used.

This means the "real" cost of an ISO exercise that triggers AMT is often closer to the time-value of the cash tied up than the full $130K nominal AMT. If you can recover the $130K credit over 5 years at a 7% real return forgone, the actual permanent cost is approximately 5 × 7% × ($130K / 2 average outstanding) = $22.75K. That's still real money, but it's an order of magnitude less than the headline AMT bill.

The dual-basis problem

When you eventually sell the ISO shares, you have two different cost bases: a regular-tax basis (your strike price, $4/share) and an AMT basis (the FMV at exercise, $52/share). Why does this matter?

• For regular-tax purposes: when you sell, the gain is sale-price minus $4, taxed at LTCG rates (assuming you held >1 year from exercise + >2 years from grant).
• For AMT purposes: when you sell, the gain is sale-price minus $52. Since you already paid AMT on the $48 spread (the bargain element) at exercise, the AMT basis is higher.

Result: your AMT capital gain is lower than your regular capital gain on the eventual sale. This is when the AMT credit recoups — for years where your regular tax > AMT, you can apply the credit to reduce your regular tax bill back toward the AMT level.

The disqualifying-disposition trap

If you sell the ISO shares within the same calendar year as exercise (or within 1 year of exercise, or within 2 years of grant), you trigger a "disqualifying disposition." The shares are retroactively treated as NSOs:

• The bargain element is taxed as ordinary income (W-2-like, your marginal bracket — 32% or 37% federal at HNW levels, plus state).
• The AMT calculation no longer applies to those shares (since they're now NSO-style). No AMT bite.
• You don't get the LTCG-on-spread benefit you exercised early to capture.

For someone in the 37% bracket, an early-disposition exercise of 10,000 ISOs at the same numbers above creates ~$177,600 of federal ordinary income tax on the bargain element. That's more than the AMT bite ($130K). But you have the cash from the sale to pay it.

The math of "exercise-and-hold vs exercise-and-sell" is fundamentally about whether you believe in the company's stock for the next 2-5 years and whether you can fund the AMT in cash. There's no universally correct answer.

Three operational rules for AMT-aware exercise

1. Run the AMT calculation BEFORE you exercise. Most CPAs will model it for you in 30 minutes if you bring your YTD W-2, expected bonus, and the ISO grant details. HELM's Scenario builder runs a simplified AMT estimate against any ISO position you log — useful for a first-pass before talking to your CPA. Both tools agree on the high-level number.
2. Exercise early in the year, not late. Exercising in January gives you 12 months to evaluate whether to do a disqualifying disposition (sell same-year, take ordinary income tax, avoid AMT) or hold (pay AMT, hope for LTCG on eventual sale). Exercising in November forces the decision before you have data on the company's trajectory.
3. Reserve cash for AMT before exercising. Rule of thumb: budget 30% of the bargain element in cash for AMT. If you can't cover that, don't exercise — or exercise fewer shares. The exercise that breaks your cash flow doesn't help you.

The post-SALT-cap dynamics

The 2017 TCJA capped SALT deductions at $10K, which closed a major historical AMT exposure for filers in CA/NY/NJ — they used to deduct large state tax bills against regular tax, which made regular tax artificially low and triggered AMT. With SALT capped, regular tax stayed higher, AMT got triggered less.

The SALT cap is scheduled to sunset at the end of 2025 unless Congress extends it. If it sunsets, AMT exposure expands again for 2026 forward — particularly for HNW operators in high-tax states. The Congressional extension picture is uncertain at the time of writing; check current status before relying on either outcome.

Regardless of the SALT-cap fate, ISO exercises specifically continue to trigger AMT because the bargain element is an AMT preference item that doesn't depend on the SALT mechanics.

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