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Leaving a startup — whether by choice, a layoff, or a life change — starts a clock that most employees don't fully understand until it's already ticking. That clock is the post-termination exercise period (PTEP): the limited window you have to exercise your vested stock options after your employment ends. Miss the deadline, and options you spent years earning can quietly disappear.
For a lot of people, the post-termination exercise period is the single most consequential — and least discussed — clause in their entire equity package. In my years writing about equity compensation, I've seen too many talented employees walk away from tens of thousands of dollars simply because no one explained the standard 90-day exercise window for stock options to them before they resigned. This guide breaks down what the PTEP is, why that 90-day default exists, what exercising actually costs, and the strategies available when the deadline is bearing down.
A post-termination exercise period (PTEP) is the amount of time — defined in your company's stock plan and your individual grant agreement — during which you can exercise your vested options after leaving the company. Vesting earns you the right to buy shares at your strike price; the PTEP governs how long that right survives once you are no longer an employee. Any vested options you haven't exercised by the end of the window are typically forfeited back to the company's option pool.
The most common default is 90 days. From your last day of employment, you generally have three months to come up with the cash to exercise — and, in many cases, to cover the tax bill that exercising can trigger. Unvested options are usually cancelled immediately on termination, so the PTEP applies only to the options you have already vested. Understanding the PTEP stock options rules buried in your paperwork is something worth doing long before you hand in your notice.
There's an important tax wrinkle here. Incentive stock options (ISOs) lose their favorable tax status if you exercise more than 90 days after leaving — after that, they are treated as non-qualified stock options (NSOs) for tax purposes. This threshold, described in the IRS guidance on stock options, is a big reason the 90-day exercise window for stock options became an industry norm in the first place.
It's a common misconception that the law requires a 90-day window. It doesn't. The only hard rule the tax code imposes is the ISO-to-NSO conversion described above; everything else is convention. Historically, companies adopted the 90-day exercise window because it was simple to administer, aligned neatly with the ISO threshold, and — bluntly — because it let departing employees' unexercised options flow back into the pool for future hires.
That default made more sense in an era when startups went public within a few years. Today, companies stay private far longer, which means an employee who leaves after four years may face a decade or more before any liquidity event. The 90-day clock, designed for a faster era, can force an uncomfortable choice: pay a large sum out of pocket to exercise illiquid shares, or forfeit them entirely.
Exercising isn't free. Your exercise cost equals your strike price multiplied by the number of options you're exercising. Consider an employee with 20,000 vested options at a $2.00 strike price. Exercising all of them costs $40,000 in cash — before any taxes. If the company's current 409A fair market value is $12.00 per share, that $10.00 spread per share can also create a taxable event.
How that spread is taxed depends on the option type. For NSOs, the spread is taxed as ordinary income at exercise. For ISOs, the spread is generally not subject to ordinary income tax at exercise, but it is a preference item for the alternative minimum tax (AMT) — a trap that has blindsided many employees who exercised into a paper gain and then owed real cash to the IRS. Every situation is different, so consult a qualified tax professional before you exercise; the figures here are illustrative, not advice. If you're weighing whether the cost is worth it, our guide on how to pay for stock options walks through the funding paths.
Stack the pieces together and the squeeze is obvious: within the 90-day exercise window, a departing employee might need $40,000 to exercise plus a five-figure tax liability, all to own shares they cannot sell. For many, that is simply not feasible, and the options lapse.
A concrete example makes the countdown real. Imagine Maya, a senior engineer who joined a Series B startup and is now leaving after four years. She has 15,000 vested ISOs at a $1.50 strike, and the latest 409A pegs fair market value at $9.00. To exercise everything within her 90-day exercise window for stock options, she needs $22,500 in cash. The $7.50-per-share spread — $112,500 in total — becomes an AMT preference item, potentially adding a five-figure tax bill on top. Maya's shares, meanwhile, remain completely illiquid; there is no public market and no announced tender offer.
Maya's realistic choices come into focus quickly. She can scrape together enough to exercise and hold, tying up meaningful savings in one illiquid bet. She can exercise only a portion to manage the AMT hit. She can seek third-party financing. Or she can let some or all of the options go. None of these is obviously the right answer — it depends on her conviction in the company, her liquidity, her tax situation, and how concentrated she's willing to be. That is exactly why starting the analysis before the PTEP clock starts matters so much.
When your PTEP is counting down, you generally have a handful of paths. You can exercise and hold, betting on a future exit. You can exercise and sell through a secondary market or a company tender offer, if one is available, to recoup your costs. You can pursue third-party option financing, where an outside party funds the exercise and taxes in exchange for a share of the upside. Or you can let the options expire. Deciding whether to buy in at all is its own analysis — our complete guide on whether you should buy your equity is a good starting point.
Whatever you choose, be honest about the risk. Concentrating a large chunk of your net worth in a single private company is exactly the trap that leaves so many stock and option holders exposed. According to investor-education resources published by the SEC, diversification is one of the most reliable ways to manage that kind of single-position risk — and the past performance of any one startup is never a guarantee of future results.
Recognizing how punishing the 90-day default can be, a growing number of companies have moved toward extending the post-termination exercise period — sometimes to seven or even ten years after departure. This shift gained real momentum in the mid-2010s, when firms like Pinterest, Quora, and Coinbase publicly adopted extended windows, framing them as a fairer deal for employees who helped build the company.
The trade-off is nuanced: extending the window past 90 days converts ISOs to NSOs, so the more generous policy carries a tax cost of its own. Heading into 2026, with the IPO pipeline still thawing and many companies choosing to stay private longer, an extended PTEP has become one of the more valuable — and negotiable — terms in an equity package. It's worth asking about before you sign an offer, not after you resign.
Here's the strategic tension at the heart of every PTEP decision: a ticking deadline pressures you to double down on a single company at the worst possible moment for objectivity. The healthier question isn't just “can I afford to exercise?” but “do I want this much of my wealth tied to one outcome?” Equity pooling offers a different path — instead of betting everything on your employer's exit, you can gain diversified exposure across a portfolio of startups. Our introduction to equity pooling explains how the model works.
If you're staring down a post-termination exercise period and weighing your choices, it helps to model the numbers first. Aption's equity simulator lets you see how a diversified equity position compares to holding a single concentrated stake, and if pooling looks like a fit, you can get a personalized offer to explore your options. The goal is simple: make your PTEP stock options decision from a position of information and choice, rather than a last-minute scramble against the clock.
Rachel Stern is a contributing author. The author name used in this article may be a pen name or pseudonym and is used for illustrative and editorial purposes only. This article is for informational purposes only and does not constitute investment, tax, or legal advice. Consult qualified professionals before making financial decisions. Past performance and hypothetical scenarios are not guarantees of future results.
Rachel is a private wealth blogger focused on equity compensation, tax planning, and portfolio diversification strategies for tech professionals.