Stock Option Post-Termination Exercise
Post-termination exercise window — the deadline and the last day the market is open to act.
Written and maintained by Paul Clark, Redmoon Software · Rules last verified · Sources
These calculators are for informational purposes only and do not constitute legal, financial, or professional advice.
How the Stock Option Post-Termination Exercise works
The Stock Option Post-Termination Exercise calculator returns the last day a departing employee can exercise vested options, and separately the last day the market is actually open to do it. The default window is 90 days, which is the standard term in the great majority of US plans, and it is adjustable because plans differ.
The window itself runs in <strong>calendar days</strong>, not trading days — a distinction this page previously got wrong in its own description. Ninety days from a Friday departure is ninety calendar days later regardless of what the market is doing. Where trading days do matter is at the end: if that ninetieth day is a weekend or a market holiday, you cannot place an exercise on it, so the calculator also reports the last day the market is open at or before the deadline. That figure is computed against the exchange calendar rather than the federal one, which matters because the market closes on Good Friday and does not close on Columbus Day or Veterans Day.
Three things worth knowing that the arithmetic will not tell you. The 90-day window is a tax rule as much as a plan term: incentive stock options generally lose ISO treatment if exercised more than 90 days after termination, converting to non-qualified options with ordinary-income consequences at exercise. Some plans extend the window for death or disability, commonly to twelve months. And exercising is a purchase — you need the strike price in cash, plus in most cases withholding on the spread, which for an appreciated private company can be a large bill with no market to sell into. Model the tax before the deadline forces the decision.
Worked example
An employee’s last day is Wednesday, 1 April 2026. Ninety calendar days later is Tuesday, 30 June 2026 — that is the deadline in the plan document. Because 30 June is a Tuesday and the market is open, it is also the last day to act. Had the ninetieth day fallen on Good Friday, the deadline in the plan would still have been that day, but the last day to actually place the exercise would have been the preceding Thursday, which is the figure the calculator surfaces.
Frequently asked questions
Is the 90-day window in calendar days or trading days?
Calendar days. Plan documents almost universally express the post-termination exercise period in calendar days or months, so weekends and holidays run inside it. Trading days matter only for the practical question of when you can place the order, which is why this calculator reports the deadline and the last open market day separately rather than conflating them.
What happens if I let the window lapse?
The vested options expire and are returned to the plan. There is no grace period and no general right to reinstate — this is one of the cleanest deadlines in equity compensation, and options worth a great deal have been lost to it. If the strike cost is the obstacle, address it well before the final week, because financing and cashless-exercise arrangements take time to put in place.
Does exercising inside 90 days preserve ISO treatment?
For incentive stock options, exercising within 90 days of termination is generally what preserves ISO status; exercise after that window typically converts them to non-qualified options, with the spread taxed as ordinary income at exercise. Note that ISO exercise can also trigger alternative minimum tax even inside the window. This is genuinely tax advice territory — model it with an adviser rather than from a date alone.
What this calculator does not do
A limitation you know about costs far less than one you find after the deadline. These are the specific things this tool cannot work out for you.
- The 90-day window is a tax rule, not a company rule. Your plan documents set the actual expiry, and the two can differ.
- Exercising an ISO after the statutory window does not void the option — it reclassifies it as a non-qualified option, with different tax consequences.
- It does not model AMT exposure, which is frequently the larger consideration.
Where these rules come from
The periods this calculator applies are taken from the primary sources below rather than from secondary summaries. Verify against them before relying on a date that matters.
- 26 U.S.C. § 422
Incentive stock option requirements, including the three-month post-termination exercise rule.