When to Exercise Stock Options: Vesting, Expiration, and AMT

The best time to exercise stock options sits at the intersection of three deadlines: the date your shares vest, the date the grant expires, and the tax year in which an exercise will hit your return. Vested options generally must be exercised within 10 years of the grant date, and if you leave your employer you may have as little as 90 days to act before Incentive Stock Options lose their favorable tax treatment.¹ Between those outer limits, the right moment depends on whether your grant is an ISO or a Non-Qualified Stock Option (NSO), how much the stock has appreciated since the grant, and whether an exercise this year would push you into the Alternative Minimum Tax.

Wait Until Your Options Vest

You cannot exercise a stock option the day you receive it. Companies use vesting schedules that determine when you actually earn the right to buy. A typical structure includes a one-year cliff, meaning no options vest until you have completed 12 months of employment. Leave before the cliff date and you forfeit the entire grant.

After the cliff, the rest of the grant vests in monthly or quarterly installments over the following two or three years, so a full four-year vest is common. Each installment becomes its own tranche you can choose to exercise on its own schedule. That gives you flexibility: you don’t have to exercise a tranche the moment it vests, and spreading exercises across tranches can help spread the tax bill across years.

The 90-Day Clock After You Leave

Once you leave a job, whether you quit or are let go, the deadline to exercise your vested options tightens. Federal tax law requires ISOs to be exercised within three months of your last day of employment to keep ISO tax treatment.¹ Miss that window and your ISOs automatically convert to NSOs, and any spread becomes ordinary income rather than a potential long-term capital gain.

Most companies set their post-termination exercise period at exactly 90 days to match the federal rule, though some plans extend it, and many extend to a year for departures caused by disability or death.² Even where a plan grants a longer window, any exercise after three months loses ISO status. If you miss the plan’s deadline entirely, the vested options are cancelled and returned to the company’s equity pool.

If you are planning to leave, work backward from your last day. Confirm your PTEP length, decide which tranches you want to exercise, and line up the cash for the exercise price and any taxes before you give notice.

The 10-Year Expiration Deadline

Every option grant carries an outer expiration date separate from the post-termination window. Federal law caps ISOs at 10 years from the grant date.¹ Once the decade passes the option expires permanently, even if you are still employed and the shares are fully vested. There is no mechanism to revive an expired option. NSO expiration terms are set by the company’s plan and usually follow the same 10-year convention, though no statutory cap applies to NSOs.

The practical implication: if you’re sitting on vested, in-the-money options that are approaching year nine, waiting for a better price is a bet against a hard deadline.

Timing ISO Exercises Around Holding Periods and AMT

ISOs get their special treatment only if you meet two holding periods: at least one year after exercise and at least two years after the original grant.¹ Clear both and the entire profit on sale is a long-term capital gain, taxed at a maximum federal rate of 20% for 2026.³ No regular income tax is owed at exercise when you hold through both periods.⁴

Sell before either period ends and you have a disqualifying disposition. The spread between your exercise price and the stock’s fair market value on the exercise date becomes ordinary income, taxed at rates up to 37% for 2026, and only gain above that exercise-date value gets capital gains treatment.⁴

The timing consequence is direct. If you want the long-term capital gains outcome, exercise at least one year before you intend to sell, and at least two years after the grant. If your grant is only 18 months old, exercising and immediately selling at IPO defeats the entire ISO benefit.

The AMT Trap on ISO Exercises

A qualifying ISO exercise produces no regular income tax, but it can still trigger the Alternative Minimum Tax. Under AMT, the spread between your exercise price and the fair market value on the exercise date is an adjustment that raises your AMT income in the year of exercise, regardless of whether you sell the shares.⁵ You could owe real tax on a paper gain.

For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, phasing out at $500,000 and $1,000,000 respectively.³ If a full exercise would push your AMT income well above the exemption, splitting the exercise across two or more tax years can keep each year’s spread manageable. Running the AMT calculation before you exercise, not after, is the point at which timing decisions get made.

The $100,000 Annual ISO Cap

Federal law limits the value of ISOs that can become exercisable for the first time in a single calendar year to $100,000, measured at the grant-date fair market value.¹ Anything above that threshold is treated as NSO for tax purposes even if your grant calls it an ISO. On a large or overlapping grant, part of what you exercise may carry NSO consequences no matter when you act.

Timing NSO Exercises

NSOs are simpler and, at exercise, usually more expensive. The spread between your exercise price and the fair market value on the exercise date is ordinary income in the year you exercise, whether or not you sell.⁶ Your employer reports the spread as wages and withholds federal income tax, Social Security tax (6.2% on earnings up to $184,500 in 2026), and Medicare tax at 1.45%, plus the additional 0.9% Medicare tax on earnings above $200,000.⁷

Because the tax hits in the year of exercise, NSO timing is largely income-year management. Exercising in a lower-income year, spreading across two calendar years, or pairing an exercise with deductible events can matter more than the exact date. After exercise, further appreciation is a separate capital gain; hold more than a year after exercise for long-term rates, and sell inside a year to be taxed at ordinary rates up to 37% for 2026.³

Early Exercise and the 83(b) Election

Some plans allow you to exercise before vesting. The reason to do it is tax timing. In a young company the exercise price and fair market value are usually close, so the spread at exercise is small or zero, and exercising early means little or no taxable income today.

To lock that in, you must file an 83(b) election with the IRS within 30 days of exercising.⁸ The election tells the IRS to tax you now, at today’s value, rather than later at each vesting date’s value. The 30-day deadline is absolute and cannot be extended.⁹ Miss it and you pay ordinary income tax on the spread at each vesting date, which can be far larger if the company has grown.

Early exercise also starts the ISO holding-period clocks and, for stock in a qualifying small business, the five-year clock for excluding up to $10 million in gain under the qualified small business stock rules. The downside: if you leave before those shares vest, the company can repurchase the unvested shares, usually at your original exercise price, and you paid for stock you never kept.

Timing Around IPOs and Acquisitions

A liquidity event can compress or rearrange every deadline above. After an IPO, insiders are typically bound by a lock-up agreement that blocks sales for around 180 days.¹⁰ You can still exercise during the lock-up, and doing so starts the one-year capital gains clock, so an exercise timed to the start of the lock-up can position you to sell at long-term rates soon after it lifts. You just can’t rely on the shares themselves to cover the exercise price or taxes until the lock-up expires.

In an acquisition, change-of-control provisions in the equity plan may accelerate vesting. Single-trigger acceleration vests all unvested options on close; double-trigger acceleration, which is more common, vests them only if you are also terminated without cause or resign for good reason within a set window after close. Either way, the plan documents will dictate the timing, and the exercise deadline may be compressed to the closing date. Review the plan well before a deal is signed.

Other Tax Factors That Move the Best Date

Net Investment Income Tax

Capital gains on exercised stock may be subject to the 3.8% Net Investment Income Tax if your modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly).¹¹ Those thresholds are not indexed for inflation, and a large exercise or sale can easily cross them, bringing the effective top federal rate on long-term gains to 23.8%.

State Income Taxes

Stock option income is subject to state income tax in most states. Top marginal rates run from 0% to over 13%, and the combined federal and state burden on an NSO exercise or an ISO disqualifying disposition can exceed 50% in the highest-tax states. State treatment of capital gains varies too. If a move is on the horizon, the state you exercise in and the state you sell in can both matter.

Wash Sale Rules

Selling company shares at a loss and exercising options within 30 days before or after that sale creates a wash sale.¹² The loss is temporarily disallowed and added to the basis of the newly acquired shares. An option exercise counts as an acquisition, so pairing a tax-loss sale with a nearby exercise can wipe out the loss you were trying to claim.

Watch for Forfeiture and Clawback Provisions

Vesting doesn’t always guarantee the options survive. Many plans forfeit vested but unexercised options if you are terminated for cause, typically defined to cover fraud, serious misconduct, or material policy breaches. Some plans require you to repay profits from prior exercises if you violate post-employment restrictions such as non-compete or non-solicitation clauses. Enforcement varies by state, and states hostile to non-competes may refuse to enforce forfeiture tied to them. If you are considering joining a competitor or starting a similar business, read your grant agreement’s forfeiture language before you count on the standard 90-day window.

1
Office of the Law Revision Counsel. 26 U.S. Code 422 – Incentive Stock Options
2
Carta. Post-Termination Exercise Period (PTEP)
3
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
4
Office of the Law Revision Counsel. 26 U.S. Code 421 – General Rules
5
Office of the Law Revision Counsel. 26 U.S. Code 56 – Adjustments in Computing Alternative Minimum Taxable Income
6
Internal Revenue Service. Topic No. 427, Stock Options
7
Social Security Administration. Contribution and Benefit Base
8
Office of the Law Revision Counsel. 26 U.S. Code 83 – Property Transferred in Connection With Performance of Services
9
Internal Revenue Service. Form 15620 – Section 83(b) Election Instructions
10
U.S. Securities and Exchange Commission. Initial Public Offerings, Lockup Agreements
11
Office of the Law Revision Counsel. 26 U.S. Code 1411 – Imposition of Tax
12
Office of the Law Revision Counsel. 26 U.S. Code 1091 – Loss From Wash Sales of Stock or Securities