Most stock option plans give you 90 days from your last day of employment to exercise vested options before they are canceled. That is the post-termination exercise window, and it exists because the Internal Revenue Code requires an incentive stock option to be exercised within three months of leaving the company to keep its favorable tax treatment.1Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Some employers, especially in the startup world, now offer windows of seven or ten years, but the extra time carries tax consequences that most people don’t anticipate.
The 90-Day Default and When It Starts
The clock starts on your last day of employment, whether you quit, were laid off, or lost your job in a restructuring. Equity administration platforms typically hard-code the deadline into your account, and most companies send a final notice confirming when the window closes.
Companies settled on 90 days because anything shorter would feel punitive and anything longer would trigger tax problems for employees holding ISOs. If you don’t submit your exercise request by the cutoff, your vested options are canceled and the shares return to the company’s equity pool. In almost every plan, there is no grace period, no extension request, and no appeals process. Missing the deadline is one of the most expensive mistakes a departing employee can make, and it cannot be undone.
Only Vested Options Are Yours to Exercise
The window applies only to options that have already vested. Anything still on your vesting schedule when you leave is almost always forfeited immediately on your termination date.
People routinely overestimate how much equity they actually own. If your offer letter said 10,000 shares vesting over four years with a one-year cliff, and you leave after two and a half years, roughly 6,250 shares may be vested, depending on whether your plan vests monthly or quarterly. The rest is gone. Your 90-day window applies only to the vested portion. Before you start planning how to fund an exercise, pull your vesting schedule and confirm the exact number of shares available to you.
How Your Type of Departure Changes the Window
Not every exit triggers the standard 90 days. Both the tax code and most equity plans adjust the window based on how you leave.
- Disability. If you leave because of a permanent and total disability, the tax code extends the ISO-qualifying exercise period from three months to one full year, and most plans mirror that extension.1Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options
- Death. When an employee dies while still employed, the executor of the estate typically has 12 months to exercise the vested options, giving the family time to work through probate before the options expire.
- Termination for cause. This is the harshest outcome. Plans generally define cause as serious misconduct, fraud, or criminal activity, and the window often closes on the same day employment ends. Some plans add clawback provisions that let the company recover gains from options exercised shortly before a for-cause termination.
Your plan document controls these variations. The statutory rules set the floor for ISOs; your company’s plan can be more generous with longer windows or more restrictive by forfeiting on the day you leave. Read the termination provisions in your grant agreement carefully.
Extended Windows at Startups
A growing number of technology companies now give departing employees seven or ten years to exercise. Coinbase, Quora, Flexport, Pinterest, and Kickstarter have adopted extended windows, often conditioned on two or three years of service before the extension kicks in. The logic is practical: at a private company with no public market, asking someone to come up with tens or hundreds of thousands of dollars within 90 days to buy illiquid stock is often unreasonable. A longer window lets you wait for an IPO or acquisition before writing a check.
The board must formally amend the equity plan to adopt an extended window, and individual grant agreements are updated to reflect the new expiration. Some companies apply the extension only to shares that vest after the policy change; others make it retroactive. If your company announces an extended window, confirm whether your existing grants are covered or only future ones.
The practical benefit is real, but a longer window does not preserve the tax treatment of an ISO past the 90-day mark. That’s the trap most employees miss.
ISOs Convert to NSOs After 90 Days
Even when your employer offers a generous five- or ten-year window, federal tax law does not care. If you exercise an ISO more than three months after your last day, it automatically loses its incentive stock option status and is taxed as a non-qualified stock option.1Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options No action from you or the company is required. It happens by operation of the tax code.
The difference is significant. With an ISO exercised inside the 90-day window, you owe no regular income tax at exercise. The spread between your strike price and the fair market value is not taxed until you sell the shares, and if you meet the holding period requirements, it is taxed at long-term capital gains rates.
With an NSO, the entire spread at exercise is ordinary income in that year. Your former employer must report it on your W-2 and withhold taxes accordingly.2Internal Revenue Service. Separate Reporting of Nonstatutory Stock Option Income Mandatory withholding includes federal income tax at the 22% supplemental wage rate (37% for amounts over $1 million), Social Security tax at 6.2% up to the $184,500 wage base for 2026, and Medicare tax at 1.45% plus an additional 0.9% on earnings above $200,000 for single filers.3Social Security Administration. Contribution and Benefit Base If the ISO was exercised within the qualifying window, the company must file Form 3921.4Internal Revenue Service. Instructions for Forms 3921 and 3922
An extended window is valuable because it prevents you from losing your equity outright. It does not preserve the tax deal in your original grant. Every day past the 90-day mark, what you exercise is an NSO.
The AMT Hit on an On-Time ISO Exercise
Exercising ISOs within the 90-day window preserves their favorable tax status, but you can still owe a substantial tax bill the same year. The spread between your strike price and fair market value at exercise is an adjustment for the alternative minimum tax.5Office of the Law Revision Counsel. 26 USC 56 – Adjustments in Computing Alternative Minimum Taxable Income Regular tax rules ignore the spread until sale. The AMT calculation adds it back.
For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, with phaseouts starting at $500,000 and $1,000,000 respectively.6Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 If your ISO spread is large enough to push your AMT income above the exemption, you’ll owe AMT on the excess, even though you haven’t sold a share and may have no cash to cover the tax.
This catches people off guard at startups, where a low strike price and a high 409A valuation can produce an enormous spread. Run the AMT calculation before you submit the exercise request. The tax can reach tens of thousands of dollars on paper gains you cannot yet turn into cash. AMT paid does generate a credit you can use in future years when you sell and pay regular tax, but that credit does not solve an immediate cash crunch.
The Holding Periods for Capital Gains Treatment
Exercising an ISO within 90 days is only the first requirement for long-term capital gains treatment. You must also hold the shares at least one year after exercise and at least two years after the original grant date before selling. Sell before both are met, and the transaction is a disqualifying disposition. The gain is taxed as ordinary income, as if the options had been NSOs from the start.
This creates a real dilemma at private companies. You exercise within 90 days to preserve ISO status, then hold shares you cannot sell, hoping a liquidity event lands after the holding periods close. If the company goes public 11 months after you exercise and you sell right away, you’ve lost the tax benefit you were trying to protect.
Paying for the Exercise When the Shares Aren’t Liquid
The hardest part of exercising at a private company isn’t the paperwork. It’s funding the purchase. Your strike price might be manageable on its own, but AMT on ISOs or income tax withholding on NSOs can push the total far beyond what you have in savings. A few paths exist, none of them free.
- Personal funds. The simplest option. If you can afford it, cash avoids interest and complexity. Just don’t drain your emergency fund to buy illiquid stock in a company that may never have a liquidity event.
- Non-recourse financing. Specialty lenders will front the exercise cost and tax bill using your shares as collateral. These loans are non-recourse, so if the company fails and the shares become worthless, you owe nothing. Origination fees typically run 3% to 6%, interest rates range from roughly 7% to 10%, and many providers also charge an incentive fee (a percentage of the shares’ value at a future liquidity event) that can run 5% to 10% at established pre-IPO companies. Repayment is due when a liquidity event occurs.
- Tender offers. Some private companies periodically run tender offers that let shareholders, including former employees, sell a portion of their shares back to the company or to an outside buyer. Timed right, proceeds from selling some shares can fund the exercise of the rest. SEC rules require these offers to stay open at least 20 business days, and the company typically sets eligibility and sale limits.
Each path trades off cost, risk, and control. Non-recourse financing has grown into a meaningful industry, with deal sizes from $25,000 into the tens of millions and durations of two to five years, but the fees add up and you are sharing your upside with the lender. Run the numbers on what you will actually net before committing.
What to Pull Together Before Your Window Closes
The worst time to start sorting out your options is the week before the window expires. As soon as you know you are leaving, collect the following:
- Number of vested shares. Confirm against your vesting schedule, not your total grant. The equity portal should show a current vested balance.
- Strike price per share. Fixed in your grant agreement. Multiple grants will likely have different strike prices.
- Current fair market value. For public companies, the stock price. For private companies, the most recent 409A valuation. The spread between strike and FMV drives both your tax exposure and whether exercising makes financial sense.
- Exercise deadline. The exact date and time your window closes. Don’t assume exactly 90 calendar days. Check the grant notice.
- Option type. Whether each grant is an ISO or an NSO determines the tax treatment. The grant agreement or equity portal should specify.
With that information in hand, talk to a tax advisor before you exercise. The interaction between ISO status, AMT exposure, NSO withholding, and your overall income for the year is complicated enough that a few hundred dollars of professional advice can save thousands. That conversation matters most if you are exercising past the 90-day mark, since the automatic conversion to NSO treatment changes the withholding obligations significantly.