ISO 90-Day Exercise Window + AMT Trap at Layoff

Who this applies to#

When you are laid off, every vested incentive stock option you hold enters a countdown. Under 26 U.S.C. § 422(a)(2), an ISO retains its special tax status only if exercised while the holder is employed or within three months of separation. Miss that window and the option automatically converts to a nonqualified stock option (NSO), permanently surrendering the favorable tax treatment ISOs offer: no income at exercise, potential for long-term capital gain treatment on the full spread, and the ability to defer ordinary income recognition until you sell. The three-month clock is non-negotiable by statute. Neither your employer nor a new employer can restart it, and severance pay does not extend it. The clock begins on your official last day of employment — not the date USCIS processes anything, not the date you receive your final paycheck, and not the date your health insurance ends. Your termination letter or the official last day in your separation agreement is day zero. This creates a decision that must be made quickly, often under financial stress, and under a tax rule that is counterintuitive: exercising an ISO does not generate ordinary income, but it does generate an Alternative Minimum Tax (AMT) preference item equal to the full spread between the exercise price and the fair market value on the day of exercise.

What changes for you#

The AMT trap is the central hazard of ISO exercise at layoff. Under 26 U.S.C. § 56(b)(3), when you exercise an ISO, the spread — the difference between the FMV of the shares on the exercise date and the amount you paid (the strike price) — is included in your Alternative Minimum Taxable Income (AMTI), even though it is not ordinary income under the regular tax system. This preference item is added to your other AMTI, and if your total AMTI after the AMT exemption exceeds your regular taxable income plus the AMT threshold, you owe AMT at 26% on the first $244,500 of excess AMTI and 28% above that (2026 thresholds per Rev. Proc. 2025-32, adjusted annually for inflation). The trap closes when the stock price later drops. If you exercise ISOs in April of your layoff year at a $50 spread and the stock falls to $10 by December, you owe AMT on the $50 spread but can only sell the stock for $10 over strike — a net loss after tax. The § 56(b)(3) rule does provide one partial escape: if you complete a disqualifying disposition of the shares in the same calendar year as exercise (selling before meeting the two-year/one-year ISO holding periods), the AMT preference item is limited to the actual gain on that sale. This is the statutory mechanism embedded in § 56(b)(3)’s cross-reference to § 422(c)(2). For ISOs held through the window and exercised, the path to long-term capital gain treatment requires satisfying both of two holding periods: the shares must be sold more than two years after the option grant date AND more than one year after the exercise date. If both holding periods are met, the entire spread (plus any post-exercise appreciation) is taxed at long-term capital gains rates — currently 15% or 20% depending on income — rather than as ordinary income. If either holding period is missed (a disqualifying disposition), the spread at exercise is ordinary income reported on your W-2 in the year of sale. The AMT credit under 26 U.S.C. § 53 partially mitigates the AMT paid at exercise. The credit can offset your regular tax liability in future years when you owe less AMT than regular tax — but the carryforward can take years to fully recover, and it does not help with the year-of-exercise cash flow problem. If you face a large AMT bill from ISO exercise and cannot pay it, the IRS offers installment agreements, but interest accrues from the original due date.

Decision tree#

1. If You hold ISOs and your layoff date is approaching

   Then → Calculate the spread on all vested ISOs (current FMV minus strike price) and model the AMT liability before deciding whether to exercise during the 3-month window. The spread is an AMT preference item whether or not you sell the stock.

   Else: If you hold NSOs, the 3-month ISO window does not apply — NSO exercise timing is driven by your grant agreement and ordinary income recognition at exercise under 26 CFR § 1.83-7.

2. If The AMT cost of exercising all ISOs now exceeds the cash you have available

   Then → Consider exercising only the tranches with the largest spread while leaving underwater or low-spread ISOs to lapse. Consult a tax advisor about the AMT credit carryforward under 26 U.S.C. § 53, which can offset future regular tax in years you do not owe AMT.

   Else: If the total AMT liability is manageable, exercise within the 90-day window to lock in ISO status and start the clock for long-term capital gain treatment (2-year hold from grant date AND 1-year hold from exercise date).

3. If Your ISOs are deeply in-the-money and you cannot pay the AMT without selling shares

   Then → A same-day-sale (disqualifying disposition) may be better than missing the window: you pay ordinary income tax on the spread in the exercise year but avoid a large AMT bill with no offsetting cash. IRS Publication 525 covers both outcomes.

   Else: If you can hold through year-end and the stock price drops before December 31, a disqualifying disposition in the same tax year the ISO was exercised can limit the AMT damage under the § 422(c)(2) rule via § 56(b)(3) — the inclusion is capped at actual gain.

Calculate your numbers#

Inputs default to federal assumptions; adjust to your specifics.

Action steps#

• Identify your official last day of employment — that is day zero of the 3-month ISO window. Confirm the date in writing with HR before signing any separation agreement.
• Pull your complete stock option grant agreement(s) and note the grant date, strike price, number of vested ISOs, and expiration date for each grant.
• Calculate the current spread on each ISO grant (FMV minus strike price) and model the resulting AMT preference item — multiply the aggregate spread by 26–28% to estimate AMT exposure before the regular tax computation.
• Determine whether you can pay the estimated AMT out of pocket without selling shares; if not, consider exercising only high-spread grants or a disqualifying same-year sale to cap the AMT at actual gain.
• If you plan to hold exercised shares for long-term capital gain treatment, confirm the two-year grant date and one-year exercise date holding periods per 26 U.S.C. § 422(a)(1).
• File IRS Form 6251 in the year of exercise to calculate your AMT liability and the resulting AMT credit carryforward under 26 U.S.C. § 53.
• Consult a CPA or tax attorney before the 90-day deadline expires — the AMT modeling is complex and errors after expiration are irreversible.

FAQ#

What exactly happens if I miss the 3-month ISO exercise window?

Any unexercised ISO automatically converts to a nonqualified stock option (NSO) the day after the window closes. You do not lose the option itself — you can still exercise, but you lose ISO tax treatment permanently. When you exercise an NSO, the spread at exercise is ordinary income reported on your W-2, subject to supplemental wage withholding (22% federal for the first $1M cumulative). The ISO preference — no income at exercise, long-term cap gain on the full spread — is gone.

How is AMT calculated when I exercise ISOs?

Under 26 U.S.C. § 56(b)(3), the spread at exercise (FMV on exercise date minus strike price) is added to your Alternative Minimum Taxable Income. You then compare your tentative minimum tax (AMTI minus the AMT exemption, times 26% or 28%) against your regular tax. If your tentative minimum tax exceeds your regular tax, you owe the difference as AMT. The spread does not generate ordinary income under the regular tax system — which is why the AMT was designed to capture it.

Is there any way to reduce the AMT impact if I exercise during the 90-day window?

Two options exist. First, if the stock price declines after you exercise but before December 31, you can do a disqualifying disposition (sell the shares in the same calendar year) — the § 56(b)(3) cross-reference to § 422(c)(2) caps the AMT preference at actual gain rather than the full exercise-date spread. Second, if you pay AMT in the exercise year, the amount becomes an AMT credit under 26 U.S.C. § 53 that can offset your regular tax in future years when you owe less AMT.

Does exercising ISOs count as income that affects my unemployment insurance eligibility?

No. Exercising an ISO does not generate ordinary income in the year of exercise (the AMT preference is not reportable income for unemployment purposes). The stock you acquire is not wages. Unemployment insurance eligibility is based on your prior wages from employment, not investment income.

My employer offered to extend the exercise window beyond 3 months — is that allowed?

The employer can extend the window beyond 3 months in the grant agreement, but doing so immediately converts the option to an NSO for federal tax purposes — the ISO statutory definition in § 422(a)(2) is absolute. An option exercisable more than 3 months after termination is not an ISO by statute. Some employers deliberately grant "extended window NSOs" with 1–5 year post-termination exercise windows because the ISO window is too short for employees to manage the AMT decision.

What is the holding period for ISO shares to get long-term capital gain treatment?

Two conditions must both be satisfied: the shares must be sold (1) more than two years after the option grant date AND (2) more than one year after the exercise date. Both holding periods must be met simultaneously. If either period is missed — a disqualifying disposition — the spread at exercise is treated as ordinary income in the year of sale, and only the post-exercise appreciation (if any) qualifies for capital gain treatment.

Can I exercise ISOs after I start a new job if I am still within the 3-month window?

Yes. The window is measured from separation from the granting employer, not from the date you start new employment. As long as you exercise within 3 months of leaving the company that granted the ISOs, the ISO tax rules apply regardless of whether you have already started your next job. Coordinate the timing carefully: the last day with the original employer is day zero, not the start date at the new employer.

Sources#