Do I owe tax when I exercise ISOs if I don't sell any shares?

Exercising and holding incentive stock options creates no regular federal income tax — but the spread (FMV minus strike price, times shares) is an AMT preference item. If your tentative minimum tax exceeds your regular tax after adding the spread, you owe the difference as an AMT bill even though you received no cash and sold nothing.

What is the ISO AMT preference item?

When you exercise ISOs and hold the shares, the spread (FMV minus strike) is added to your alternative minimum taxable income (AMTI) as a preference adjustment. This can push your AMTI well above your regular taxable income, triggering AMT at 26 or 28 percent on the difference — a real cash bill on unrealized appreciation.

Do I ever get the AMT back?

Yes. AMT paid on ISO exercises creates a minimum tax credit (Form 8801) that you carry forward indefinitely. In future years when your regular tax exceeds your tentative minimum tax — typically after you sell the shares and report the gain — you apply the credit to reduce your regular tax. The AMT is deferred cost, not permanent, but the cash may be tied up for years.

Does California tax ISO exercises differently than the IRS?

Yes. California and most states do not conform to federal ISO treatment. In California, the spread at exercise is taxable as ordinary income for state purposes even though it creates no regular federal income. A California employee exercising in-the-money ISOs faces both federal AMT and California state income tax on the same spread — two separate bills on unrealized, illiquid gains.

ISO exercise cost and AMT estimator

Exercising ISOs before a tender offer or IPO can convert future ordinary income into capital gains — but the spread creates a federal AMT bill now, plus state income tax in most states, with no shares sold to pay it. Estimate the real cash outlay before you commit to an exercise.

ISO options to exercise

Strike price per share ($)

Current 409A / FMV per share ($)

Estimated 2026 W-2 and other ordinary income ($) — before this exercise

Filing status

State income tax rate on ordinary income (%) — use 0 for TX, FL, WA, NV

Simplified estimate using 2026 AMT values per IRS Rev. Proc. 2025-32 as amended by OBBBA (July 2025): single exemption $90,100 / MFJ $140,200; phaseout starts at $500K (single) / $1M (MFJ) at 50 cents per dollar; 26% AMT on first $244,500 of AMTI, 28% above. Federal brackets from IRS Rev. Proc. 2025-32. Excludes FICA, NIIT, the standard deduction (slightly overstates regular tax), and any state-level AMT add-ons. State tax line uses your entered rate applied to the full spread — state ISO conformity varies; confirm your state's rules. Model the exact number with a CPA or equity-comp advisor before exercising.

How ISO AMT actually works

Incentive stock options get favorable federal treatment: no regular income tax at exercise. The catch is the alternative minimum tax:

The spread is an AMT preference item. When you exercise and hold ISOs, the spread — (FMV − strike) × shares — is added to your alternative minimum taxable income (AMTI), even though you sold nothing and received no cash.
AMT runs in parallel to regular tax. The IRS computes your regular tax and a tentative minimum tax separately. You owe whichever is higher. If the ISO spread pushes the tentative minimum tax above your regular tax, the difference is an AMT bill, due in April or as a quarterly estimated payment.
The cash is real; the shares aren't liquid yet. Many employees discover the AMT bill after the fact — spread in illiquid shares, unexpected six-figure tax, no cash to pay it. The estimator above quantifies the bill before you commit.

The classic trap: exercising deep-in-the-money ISOs in the year before an IPO — when the 409A is high but shares aren't yet liquid — maximizes AMT exposure. By the time the lockup expires, the stock may have dropped. The tax was real; the value wasn't recoverable.

When to exercise: the spread determines the AMT

AMT exposure grows proportionally with the spread. The best time to exercise ISOs is when the spread is near zero — right after a grant, or early in the company's life when the 409A is close to your strike price. That's usually the opposite of when employees feel the urgency to exercise.

Spread under 20–30% of strike price: AMT is often zero or small. Run the estimator and consider acting.
Spread above the strike price: AMT typically exceeds exercise cost. Know the total before deciding.
Tender or IPO year: Exercising ISOs in a year you already have a large liquidity event stacks a high AMTI on top of high regular income — the worst scenario for AMT. Exercise before that year if the 409A allows it.

The state trap: California and most states tax the spread as ordinary income

California does not conform to federal ISO treatment. For state purposes, the ISO spread at exercise is ordinary income — taxed immediately at state rates whether you sell or not. An employee with a $500K spread at California's 9.3% rate faces a $46,500 state tax bill at exercise, on top of any federal AMT.

Other states that tax ISO exercise spreads as ordinary income include New York, New Jersey, Pennsylvania, and most others. States with no income tax — Texas, Florida, Washington, Nevada, Wyoming, South Dakota, Alaska — create no state bill on the spread. Oregon, Massachusetts, and Colorado have different partial conformity rules; verify with a local CPA before exercising.

The AMT credit: you get it back

AMT paid on ISO exercises is not a permanent cost. It becomes a minimum tax credit (reported on Form 8801) that carries forward indefinitely. In future years when your regular tax exceeds your tentative minimum tax — typically in the year you sell the shares and report the long-term capital gain — you apply the credit dollar-for-dollar against your regular tax.

The credit softens the long-run cost of early exercise. The problem is timing: the cash is due this year; the credit may not be usable for three to five years. Some employees fund the AMT bill from other savings. Others exercise tranches across multiple years to spread the AMT over time rather than triggering it all at once.

NSO vs ISO sequencing

If you hold both NSOs and ISOs, the sequencing matters. NSO exercise creates immediate ordinary income — withholding covers most or all of the tax, and the spread doesn't create AMT. ISO exercise creates AMT instead of ordinary income. In a year with available AMT capacity (regular tax already high, spread modest), exercising ISOs uses the AMT buffer efficiently. In a year with a large RSU settlement or salary spike, the regular tax may already exceed your tentative minimum tax — making ISO exercise AMT-free that year too. The early exercise guide covers the full decision framework.

Related tools

Tender-offer net proceeds

If the tender opens before you exercise, estimate after-tax proceeds on shares or unexercised options in the window — including which instrument order minimizes total tax.

RSU settlement tax estimator

RSUs settle at the IPO at 22% supplemental withholding — estimate the federal and state gap and your quarterly payment deadline.

Early exercise and 83(b)

The 30-day 83(b) deadline, QSBS clocks, NSO vs ISO tradeoffs, and the full early-exercise decision framework for pre-IPO employees.

Model the real AMT before you exercise

The estimator gives you the shape of the number. A fee-only equity-comp advisor gives you the exact figure: FICA, NIIT, multi-state allocation, AMT credit timing, NSO vs ISO tranche sequencing, and whether exercising now vs. waiting for the tender changes the after-tax outcome. Free match, no obligation.