Equity
From 90 Days to 10 Years: What Extending the Option Exercise Window Really Costs
Extending a 90-day stock option exercise window converts ISOs to NSOs, adds ASC 718 expense, and can trigger 409A penalties if you pick the wrong end date.
By 409.AI Team - 2026-08-18
# From 90 Days to 10 Years: What Extending the Option Exercise Window Really Costs
A senior engineer resigns after four years. They hold 40,000 vested options struck at $0.42 from a 2021 grant. The company's current 409A puts common stock at $6.80. Exercising costs $16,800 in cash, and the $255,200 of spread lands on their alternative minimum tax calculation for shares nobody can sell. The clock says 90 days.
They do the math and walk away. So does the next person.
Somewhere around the third or fourth time this happens, the question reaches the CFO: can we just give people longer? The answer is yes. The mechanics are more interesting than most equity conversations get. Extending the window is legal, common, and cheap to administer, and it quietly converts incentive stock options into nonqualified ones, creates an accounting charge, hands the company a tax deduction it did not have before, and, if you pick the wrong end date, retroactively turns years of option grants into a failed deferred compensation plan.
The 90 days is the tax code showing through your plan document
Founders often assume the three-month window is boilerplate their law firm inserted out of caution. It isn't. It comes straight from the statute.
[IRC Section 422(a)(2)](https://www.govinfo.gov/content/pkg/USCODE-2024-title26/html/USCODE-2024-title26-subtitleA-chap1-subchapD-partII-sec422.htm) grants ISO treatment only if the holder was an employee of the company (or a parent or subsidiary) at all times from the grant date through the day three months before exercise. Section 422(c)(6) stretches that to one year if the person is disabled within the meaning of Section 22(e)(3). Miss the deadline and the exercise is simply not the exercise of an ISO, no matter what the grant agreement calls it.
Here is the part that gets lost. Section 422 does not say the option has to *die* at 90 days. It says ISO treatment stops. Every plan that cancels unexercised options on day 91 is making a choice, not following a rule. The tax code sets a deadline for one tax characterization; the company decided that deadline should also be a forfeiture date.
Once you separate those two ideas, extending the window becomes a design question with a known cost. If you are still working out how strike prices get set in the first place, our [walkthrough of what a 409A valuation is](https://409.ai/articles/what-is-a-409a-valuation-a-comprehensive-guide) covers the ground underneath this one.
Two sets of rules fire when you extend
Section 424: the extension is treated as a brand new grant
Treasury Regulation Section 1.424-1(e)(2) is blunt about it. Any modification, extension, or renewal of the terms of an option is considered the granting of a new option. Paragraph (e)(4)(i) then defines the term, and names this exact fact pattern: a change providing an extension of the period during which an option may be exercised, "such as after termination of employment," is a modification regardless of whether the optionee in fact benefits. Shortening the exercise period, by contrast, is not a modification. The rules run one direction only. ([26 CFR 1.424-1](https://www.govinfo.gov/content/pkg/CFR-2025-title26-vol7/pdf/CFR-2025-title26-vol7-sec1-424-1.pdf))
A deemed new grant has to clear Section 422(b)(4) on its own, meaning a strike price at or above fair market value on the modification date. Our engineer's $0.42 option, re-granted against a $6.80 FMV, fails that test on contact. So the ISO is gone twice over: once because the deemed new option is priced below FMV, and again because any exercise after the three-month mark falls outside Section 422(a)(2) anyway.
One procedural detail is worth knowing before you draft the offer letter. Under paragraph (e)(4)(iii), an *offer* to change the terms of an option that stays open for 30 days or more is itself a modification, effective the date the offer was made, even for people who decline it. An offer open for fewer than 30 days is not. Companies that run extensions as a voluntary election should keep the election period short and close it on schedule.
Section 409A: the part that can actually hurt
Options on the company's own stock, struck at fair market value on the grant date and carrying no separate deferral feature, sit outside Section 409A to begin with. An extension can drag them back in, and the drafting is unforgiving about timing. Under Treasury Regulation Section 1.409A-1(b)(5)(v)(A), if there is an extension, the option "is treated as having had an additional deferral feature from the original date of grant," which makes it a deferral of compensation from that original date rather than from the date you extended.
The consequences under [Section 409A(a)(1)](https://www.govinfo.gov/content/pkg/USCODE-2024-title26/html/USCODE-2024-title26-subtitleA-chap1-subchapD-partI-subpartA-sec409A.htm) fall on the employee: current income inclusion of all vested deferred compensation, a 20 percent additional tax on that amount, and interest at the underpayment rate plus one percentage point, calculated back to the year the compensation was first deferred and no longer at risk of forfeiture.
Then the regulation gives you the way out, and it is the reason the whole practice works. Section 1.409A-1(b)(5)(v)(C)(1) provides that it is *not* an extension if the exercise period is extended to a date no later than the earlier of the latest date on which the option could have expired by its original terms under any circumstances, or the tenth anniversary of the original grant date. ([26 CFR 1.409A-1](https://www.govinfo.gov/content/pkg/CFR-2025-title26-vol6/pdf/CFR-2025-title26-vol6-sec1-409A-1.pdf))
Work it through with real dates. A grant made in March 2019 with a standard ten-year term expires in March 2029. An employee leaves in August 2026 with a 90-day window closing in November. Push that window out to March 2029 and you have gone nowhere the option could not already have gone, so there is no extension and no 409A issue. Push it to 2031 and you have created one, retroactive to 2019.
That is why well-drafted extensions read "the earlier of seven years from termination or the original expiration date" rather than a flat seven years. The trailing clause is doing all the work.
The regulation adds one more rule that matters after a bad quarter. If the option is underwater when you extend it, meaning the exercise price equals or exceeds current fair market value, the change is treated as a modification rather than an extension, which keeps the retroactive deferral problem off the table. Companies working through what a valuation reset does to outstanding grants will find the related mechanics in our piece on [down rounds and underwater options](https://409.ai/articles/down-round-409a-underwater-options-repricing).
What the employee is actually trading
The extension buys time and sells tax treatment. Both halves deserve to be said out loud when you announce it.
At exercise, an ISO produces no regular taxable income, though [the IRS notes](https://www.irs.gov/taxtopics/tc427) that the spread may pull the holder into alternative minimum tax. A nonqualified option produces ordinary income equal to fair market value at exercise less the amount paid. That amount is wages: the company withholds on it and reports it on Form W-2, box 12, code V.
For our engineer, exercising as an NSO at the same $6.80 means $255,200 of ordinary income and a payroll tax withholding obligation the company has to collect, in cash, on stock with no market. Exercising within 90 days as an ISO means no regular income at all, and if they hold two years from grant and one year from transfer under Section 422(a)(1), the entire gain is long-term capital gain.
So the extension is worth the most to people who cannot fund an exercise today and the least to people who can. Anyone with the cash and the conviction is better off exercising inside the three months. Anyone without it was going to forfeit, and now has years to see whether the company works. The full comparison lives in our breakdown of [how ISOs and NSOs are each taxed](https://409.ai/articles/iso-vs-nso-how-stock-options-are-taxed).
Extensions are not the only tool for this problem. Early exercise paired with [an 83(b) election](https://409.ai/articles/the-83b-election-explained-for-founders) moves the tax event to a point when the spread is near zero. A company-run [tender offer or structured secondary](https://409.ai/articles/tender-offers-secondary-sales-409a-valuation) gives departing holders actual cash to exercise with. And [the 83(i) election](https://409.ai/articles/83i-election-qualified-equity-grant-tax-deferral) exists for exactly this squeeze, though almost nobody meets its conditions.
What it costs the company
Three things move, and only one of them is bad.
The tax deduction improves. Under [Section 421(a)(2)](https://www.govinfo.gov/content/pkg/USCODE-2024-title26/html/USCODE-2024-title26-subtitleA-chap1-subchapD-partII-sec421.htm), a qualifying ISO exercise gives the company no compensation deduction at all. Once the option is nonqualified, Section 83(h) allows a deduction equal to the amount the holder includes in income. On $255,200 of spread that is a real number, and it is the quiet reason some CFOs stop resisting.
The accounting expense goes up. Under ASC 718-20-35-3, a modification is accounted for as an exchange of the original award for a new one. The company measures incremental fair value as the fair value of the modified award immediately after the change less the fair value of the original award immediately before it, and recognizes that increment as additional compensation cost. Lengthening the contractual term raises option fair value, so there is always an increment, and for fully vested awards it hits the income statement immediately rather than spreading over a service period. Measuring it takes an option-pricing model and a current common stock FMV, which is the same input your [ASC 718 expense calculation](https://409.ai/articles/asc-718-stock-based-compensation-startup-guide) already runs on. If you need that measurement supported, that is what an [ASC 718 valuation](https://409.ai/products/asc-718) is for.
Overhang persists. Options that would have evaporated in 90 days now sit on the cap table for years, held by people who no longer work there. That changes your available pool, your fully diluted share count, and the allocation math in every future 409A.
Getting it right
Write the long window into the grant agreement from day one if you can. There is no modification to analyze, no 409A extension question, and no awkward election period. The ISO still stops being an ISO three months after termination by operation of Section 422(a)(2), but that happens under the original terms rather than because you changed something.
If you are extending existing grants instead, cap the new deadline at the earlier of the original expiration date or the tenth anniversary of grant, keep any voluntary election open fewer than 30 days, and date a fresh [409A valuation](https://409.ai/products/409a) close to the modification. You need that number twice: to know whether the options are underwater, which changes which regulation applies, and to measure the incremental fair value your auditors will ask about.
The 90-day window is a choice you are allowed to unmake. The date you extend to is not. Stay inside the original term and this is plan design with a manageable accounting entry. Step past it and you have created a nonqualified deferred compensation plan dated to a grant you made years ago, for employees who have already left and cannot fix it. The number that decides both outcomes is the current fair market value of your common stock, which is the one thing worth having settled before the offer letters go out.