The 90-Day Exercise Window: What You Need to Know

The Most Important Deadline You'll Face

If you're leaving a startup — whether by choice, layoff, or termination — the 90-day post-termination exercise period (PTEP) is likely the most consequential financial deadline you'll face. Miss it, and years of vested stock options disappear.

The standard 90-day window means you have exactly 90 calendar days from your last day of employment to exercise any vested stock options. After day 90, those options expire. There are no extensions, no exceptions, and no way to get them back.

Why 90 Days?

The 90-day window exists primarily because of IRS rules around Incentive Stock Options (ISOs). To maintain ISO tax treatment (no ordinary income tax at exercise), the IRS requires that options be exercised within 90 days of termination. If exercised after 90 days, ISOs automatically convert to NSOs, losing their tax advantage.

Most companies set their PTEP at exactly 90 days for ISOs, and many use the same window for NSOs even though the IRS doesn't require it for that option type.

What the Clock Looks Like

Here's a timeline of what happens:

Day 0 — Last day of employment The clock starts. Your vested options are intact, but the countdown begins.

Days 1-30 — Assessment phase Gather your option agreement, check vested shares, calculate exercise cost and tax burden. This is when you should run our calculator.

Days 31-60 — Decision and funding phase Decide how many shares to exercise. Arrange funding — personal savings, financing, or a combination. Start the exercise paperwork with your company.

Days 61-80 — Execution phase Submit your exercise notice and payment. Allow time for processing — some companies take 5-10 business days.

Days 81-90 — Emergency zone If you haven't started the exercise process by now, you're in dangerous territory. Company processes, bank transfers, and administrative delays can eat up these final days.

Day 91 — Game over Unexercised options expire permanently.

What You Need to Exercise

To exercise your stock options, you typically need:

1. Your stock option agreement — this documents your strike price, number of shares, vesting schedule, and PTEP
2. Cash for the exercise cost — number of shares x strike price per share
3. Cash for taxes — AMT (ISOs) or ordinary income tax + FICA (NSOs)
4. A completed exercise notice — your company's stock administrator will provide this form
5. Payment — wire transfer, ACH, or check depending on the company

The Hidden Cost: Taxes

The exercise cost is just the tip of the iceberg. Here's what catches many employees off guard:

For ISOs: The spread (FMV minus strike price) is an AMT adjustment. If you're exercising a significant number of options, the AMT liability can be larger than the exercise cost itself. You won't owe this until you file your tax return, but you need to plan for it.

For NSOs: The spread is immediately taxable as ordinary income. Your company may withhold taxes at exercise, or you may need to make estimated tax payments. Either way, you need the cash.

Example:

• 10,000 options at $2 strike price, $20 FMV
• Exercise cost: $20,000
• Spread: $180,000
• Estimated taxes (ISO in CA): $30,000-50,000 in AMT
• Estimated taxes (NSO in CA): $60,000-80,000 in income tax + FICA
• Total cash needed: $50,000-$100,000

Companies With Extended Exercise Windows

Not all companies use the 90-day standard. Some companies have adopted extended post-termination exercise periods:

• 10 years: Some companies allow ex-employees to exercise for up to 10 years, giving much more breathing room
• 7 years: A middle ground that some companies have adopted
• 1 year: More generous than 90 days but still creates urgency

If your company has an extended PTEP, you have more time to plan — but don't procrastinate. Tax laws change, company valuations change, and your financial situation changes.

Important note about ISOs: Even with an extended PTEP, ISOs lose their ISO tax treatment after 90 days of termination. If you exercise in month 4, they'll be treated as NSOs for tax purposes. This matters because NSOs trigger ordinary income tax and FICA at exercise, while ISOs only trigger AMT.

Strategies for the 90-Day Window

Start Planning Before You Leave

If you know you're leaving (by choice), start planning your exercise strategy while you're still employed. Calculate your costs, explore financing, and save up if possible.

Exercise Partially

You don't have to exercise all or nothing. If you can only afford to exercise 2,000 of your 10,000 vested options, that's better than exercising zero.

Consider Early Exercise

Some companies allow you to exercise options before they vest (early exercise). Combined with an 83(b) election, this can significantly reduce your tax burden. But you need to do this while you're still employed.

Explore Financing

Stock option financing can provide the capital to exercise. Non-recourse financing is particularly attractive because you're protected if the company fails — you only repay from liquidity proceeds.

Talk to a Tax Professional

The tax implications of exercising are complex, especially with ISOs and AMT. A tax professional who specializes in stock compensation can help you optimize your strategy.

Don't Let Your Options Expire

The saddest outcome is letting vested options expire because you didn't plan ahead. According to industry data, about 76% of startup employees never exercise their options. Many of those forfeitures happen during the 90-day window — employees simply run out of time or can't come up with the cash.

Start by understanding your numbers. Our free calculator shows you exactly what exercising would cost, broken down by exercise price, federal taxes, state taxes, and FICA. From there, you can make an informed decision about how to proceed.