The Ninety-Day Clock: What happens to my stock options if I quit?
Incentive stock options keep their tax break for only three months after you leave. Exercise later and the gain is taxed like salary, not stock.
Someone who leaves a startup usually has 90 days to exercise their stock options, meaning buy the shares at the price the grant promised. That deadline is in the option agreement, and it is the one people know about.
There is a second one, and it is in the tax code. An incentive stock option keeps its favorable tax treatment only if you exercise within three months of your last day. On day 91 the option still exists, but the same exercise is taxed like a bonus, at wage rates, instead of like a stock sale at the lower capital gains rate.
Two clocks, one number. That is the whole problem.
How much money are we talking about?
Enough that the day matters.
Christine is leaving a private company with 20,000 vested incentive stock options at a $4 strike, the price she is allowed to pay per share, on stock now worth $24 a share. Exercising means writing an $80,000 check for private stock she cannot sell yet.
It also creates a $400,000 gap between what she pays and what the shares are worth. Whether that gap is taxed at capital gains rates or wage rates depends on which side of day 90 she exercises, and the difference runs to five figures.
Wait, what actually happens to my options when I leave?
Unvested options return to the company. Vested options are yours to exercise, for a limited time.
The time limit comes from your option agreement, not from the IRS. Most plans give you 90 days after your last day to exercise vested options, and anything you have not exercised by then expires. Some companies have stretched that window to five, seven, or ten years, so their employees are not forced to write a large check in the middle of a job change. The IRS does not object to a longer window. It just stops treating the option the same way.
Before going further, it helps to know what kind of option you hold. Startups grant two kinds:
- An incentive stock option (ISO) creates no regular income when you exercise. The gap between your strike and the share's value, the spread, shows up only in the alternative minimum tax. That is a second tax the IRS figures alongside the regular one, and you pay it in any year it comes out higher. That letter is the long version. Hold the shares long enough and the entire gain from your strike price is taxed as a long-term capital gain, 20% federal plus the 3.8% investment tax.
- A nonstatutory stock option (NSO) creates income the day you exercise. The spread is treated as wages: taxed at your ordinary rate, up to 37% federal, plus Medicare taxes, reported on a W-2, with withholding taken at exercise.
Your grant paperwork says which one you have. Christine's are ISOs, which is why the second clock matters.
Why does the 90th day change my taxes?
Because the tax code only lets an ISO be exercised by an employee.
Section 422 requires that you be an employee of the company, its parent, or a subsidiary at all times from the grant date until three months before the exercise date. That is the rule that makes the option "incentive" in the first place. Once you have been gone longer than three months, the exercise no longer qualifies, and the tax code treats it the only other way it can: as an NSO.
Nothing on the option itself changes. Your strike, your share count, your expiration date all stay the same. Only the way the gain is taxed flips.
The clock counts employment, not involvement. Moving between the company and a parent or subsidiary does not start it. Staying on as a contractor or advisor does, even if you still have a badge and a seat on the cap table, because an ISO can only be held by an employee. If the company is open to it, ask for the change to be documented as a leave of absence: a leave of up to three months, or longer when the right to return is guaranteed by contract, counts as continued employment.
Two edge cases bend the schedule. If you leave because of a disability, the three months becomes twelve. If an option holder passes away, the clock does not run at all for the family who inherits the options. Everyone else is on the standard schedule.
How much does exercising on day 91 actually cost?
The same exercise, one day apart, produces two different tax bills. Christine files single on a $220,000 salary, and the spread on her exercise is $400,000 either way.
- EmployedIncentive stock option
- Spread counted only by the AMT calculation
- $118,600 in April, credited back later
- 90 days after leavingStill an incentive stock option
- Same exercise, same AMT calculation
- $118,600 in April, credited back later
- Day 91 onwardNonstatutory stock option
- Spread taxed as wages, up to 37% plus Medicare
- $147,800 at exercise, not credited back
Within 90 days, the exercise is an ISO exercise. Her regular tax does not move. The AMT calculation adds the $400,000 spread to her income and comes out $118,600 higher than her regular tax, so that is the check she writes in April. It is a prepayment, not a cost: the IRS records the $118,600 as a minimum tax credit and subtracts it from her tax bills in later years, usually the year she sells. At the sale, the whole gain from $4 upward is a long-term capital gain.
On day 91, the exercise is an NSO exercise. The $400,000 is added to her wages. It costs $138,400 in additional income tax and $9,400 in Medicare taxes, about $147,800 total, and it is due at exercise. Because she no longer works there, the company will typically ask her to pay the withholding in cash before it releases the shares. None of it comes back. In exchange, the IRS treats her as having paid $24 a share, so only growth above $24 is a capital gain later.
Suppose she holds the shares and sells at $50 three years later. The ISO path owes capital gains tax on $920,000, every dollar above her $4 strike. The NSO path owes it on $520,000, the growth above $24, because the first $400,000 was already taxed as wages.
| Exercised within 90 days | Exercised on day 91 | |
|---|---|---|
| Federal tax at exercise | $118,600 | $147,800 |
| Tax at sale | $219,000 | $123,800 |
| AMT credit returned | −$118,600 | — |
| Lifetime federal tax | $219,000 | $271,600 |
Christine's exercise run both ways, rounded. Single filer, $220,000 salary, 2026 federal rules, before state tax. Gains at sale are taxed at 23.8%, and the AMT credit is assumed to return in full by the year of sale.
The difference is about $52,600, or roughly 13 cents on every dollar of spread. That is the gap between the 23.8% capital gains rate and the roughly 37% she pays all-in on wages, applied to $400,000, and it exists because she exercised one day too late. All of this is before state tax. California taxes both kinds of income at the same rates, so the state does not widen the gap, but it does add its own bill on top of every number above.
My company gave me ten years to exercise. Doesn't that solve it?
It solves the first clock. It cannot touch the second.
An extended window means your options do not expire on day 90. It does not keep them ISOs. Companies with long windows know this, which is why their agreements usually say the options convert to NSOs three months after termination. Some plans skip a step and grant NSOs from the start.
The extended window still changes the decision, though, because it changes when you have to pay. With 90 days, Christine has to find $80,000 for the shares and $118,600 for the AMT within one quarter, for private stock she cannot sell and that may never be worth $24. With ten years, she can wait for a tender offer or an IPO and exercise on the same day she sells. Every dollar of the spread is taxed as wages at that point, but the money to pay it arrives at the same moment, and if the company never gets there, she is out nothing.
That is the honest trade. The ISO path is cheaper in total. The NSO path never asks you to put your own cash at risk.
What should I ask before my last day?
Three questions, in this order. Ask the equity administrator or the stock plan portal, not your manager:
- How many days do I have to exercise after termination? Read the number in the plan, not the number people repeat.
- Which of my vested options are ISOs and which are NSOs? Grants often mix the two, and the clock only matters for the first kind.
- What is the current 409A price, and what is my spread? The 409A is the company's formal appraisal of a private share. The gap between it and your strike is the number both tax calculations run on.
If the plan converts your options to NSOs after 90 days, ask what the withholding process looks like for a former employee. Most companies require the cash up front, and the flat 22% that payroll withholds on anything other than a regular paycheck is almost never the rate you actually owe.
When is exercising inside the 90 days the right call?
When you can afford to be wrong about the company, and when the spread is worth protecting.
The ISO path asks for two checks on private stock: the strike price now and the AMT in April. Christine's total is almost $200,000, and if the company never sells, none of it comes back. Exercising inside the window makes sense when you could absorb that outcome, when you believe the shares will be worth more than $24, and when the spread is large enough that 13 cents on the dollar matters. At a $400,000 spread it is $52,600. At a $40,000 spread it is closer to $4,000, and the AMT's own limit may cover the whole exercise anyway.
Start with the plan document, not the tax code. Find your window, find your spread, and decide before day 90 does it for you.
If you cannot fund the exercise, letting the options convert is a rational choice, not a mistake. It costs a higher rate later in exchange for never being out of pocket. The real mistake is not knowing there were two clocks until the second one has already run out.