What Are Option Grants and How Do They Work?

A stock option grant is your employer’s promise that you can buy a set number of company shares at a locked-in price after you’ve earned the right to do so. How stock option grants work comes down to four moments: the grant, when the price and terms are fixed; vesting, when the options become yours to use; exercise, when you actually buy the shares; and sale, when you cash out. The tax bill at each moment depends on whether the grant is an incentive stock option (ISO) or a non-qualified stock option (NSO), and the difference between those two paths can be worth tens of thousands of dollars on the same number of shares.

The Life of an Option Grant

The clock starts on the grant date. That’s when your company issues you the right to buy a specific number of shares, and it’s the date your exercise price (also called the strike price) is set. Companies almost always fix the strike at the stock’s fair market value on that day. Setting it lower carries serious tax penalties, which we’ll come back to.

You can’t buy shares right away. Options become available on a vesting schedule, and a common one is four-year vesting with a one-year cliff: you earn nothing for the first twelve months, then 25% of your options vest at once on your one-year anniversary, with the remaining 75% vesting in monthly or quarterly installments over the following three years.

Once options are vested, you exercise them by paying the strike price for each share. If the stock is worth more than what you’re paying, the options are “in the money.” If the stock has dropped below your strike, they’re “underwater,” and there’s no reason to exercise since you’d be overpaying for shares you could buy on the open market. After you exercise, you own actual shares and become a shareholder.

ISOs vs. NSOs

The tax code splits stock options into two categories, and which one you hold controls when and how much tax you owe.

ISOs come with strict eligibility rules. They can only go to employees, not contractors, advisors, or board members. The option must be granted under a shareholder-approved plan, can’t be exercisable more than ten years after the grant date, and the strike price must be at least equal to the stock’s fair market value when granted.¹ There’s also a $100,000 annual cap: if the fair market value of stock becoming first exercisable in any calendar year exceeds $100,000, the excess options are automatically reclassified as NSOs.²

NSOs are the default. Any option that doesn’t meet every ISO requirement is an NSO. Because NSOs carry no statutory eligibility restrictions, companies can grant them to employees, independent contractors, directors, and outside advisors.

What You Owe When You Exercise NSOs

NSO taxation is straightforward. Nothing happens at grant, nothing happens at vesting, and the tax bill arrives when you exercise.

At exercise, you owe ordinary income tax on the “spread,” which is the difference between the stock’s current market value and the strike price. If your strike is $5 and the stock is worth $25 the day you exercise, you have $20 per share of ordinary income. That income shows up on your W-2 in Box 1, and your employer withholds federal income tax, Social Security, and Medicare as with a regular paycheck.³ Federal withholding on supplemental wages like option exercises is typically a flat 22% for amounts up to $1 million and 37% above that, which often underpays your actual tax bracket, so plan for a possible balance due at filing time.

After exercise, your tax basis in each share equals the strike price plus the ordinary income you already recognized. From there, any further gain or loss is a capital gains event. Sell within one year of exercise and you pay short-term capital gains rates, which match ordinary income rates. Hold longer than one year and the gain qualifies for long-term capital gains rates, which top out at 20% for most high earners in 2026.⁴ If the stock drops after exercise, you can claim a capital loss.

What You Owe When You Exercise ISOs

ISOs offer a genuinely better tax deal, with more complexity. When you exercise an ISO, you owe zero regular federal income tax on the spread. No withholding, no W-2 entry, no Social Security or Medicare hit.⁵

The catch is the alternative minimum tax. The spread at exercise counts as an AMT adjustment item, which can push you into owing AMT even if you’ve never dealt with it before.⁶ A large ISO exercise can blow past the AMT exemption thresholds easily. You calculate your AMT exposure on Form 6251, and if the AMT exceeds your regular tax, you pay the difference.⁷

Qualifying Dispositions

The full ISO tax advantage only kicks in if you meet two holding requirements when you sell: at least two years from the grant date and at least one year from the exercise date.¹ Meet both, and the entire gain from strike price to sale price is taxed as long-term capital gain. No ordinary income, no employment taxes.

Disqualifying Dispositions

Sell before satisfying both holding periods and you trigger a disqualifying disposition, which retroactively converts part of your gain to ordinary income. The ordinary income portion equals the lesser of two amounts: the actual gain you realized on the sale, or the spread that existed on the day you exercised. Any remaining gain above the exercise-date fair market value is taxed as a capital gain, short-term or long-term depending on how long you held the shares after exercise.⁴

The “lesser of” rule matters when the stock drops after exercise. If you exercised at a $20 spread but sold at only a $12 gain, you owe ordinary income tax on $12 per share, not $20.

Getting AMT Back Later

AMT paid on an ISO exercise isn’t gone forever. Every dollar of AMT you pay on the ISO spread generates a minimum tax credit under IRC Section 53, which you can use in future tax years when your regular tax exceeds your tentative minimum tax.⁸ The credit never expires. In practice, recovering the full amount often takes several years, and the time value of waiting is a real cost that people routinely underestimate when planning large ISO exercises.

How You Pay the Strike Price

When you’re ready to exercise, companies typically offer a few ways to pay:

Cash exercise. You pay the strike price out of pocket and receive the shares. This requires the most upfront capital but gives you the most control over holding period and tax timing.
Sell-to-cover. You exercise and immediately sell just enough shares to cover the strike price, taxes, and fees, keeping the rest. This is the most common method at public companies because it requires no cash outlay.
Cashless exercise (same-day sale). You exercise and sell all the shares in a single transaction, pocketing the after-tax spread in cash. You never hold stock, which eliminates market risk and also eliminates any chance of long-term capital gains treatment.

For ISOs specifically, a cashless exercise or same-day sale will almost certainly trigger a disqualifying disposition, because you can’t meet the one-year-from-exercise holding period if you sell immediately. The ISO tax advantage only works when you hold the shares.

Deadlines That Can Erase the Grant

Stock options don’t last forever. ISOs cannot have a term longer than ten years from the grant date under federal law.¹ Most NSO plans also use a ten-year term, though they aren’t legally required to. Any options you haven’t exercised by the expiration date simply vanish.

The more pressing deadline hits when you leave the company. Most option plans give departing employees a window, often just 90 days, to exercise any vested options before they’re forfeited. For ISOs, that window isn’t just company policy: federal law requires ISOs to be exercised within three months of leaving employment to retain their tax-favored status.¹ If a company extends the window, any ISOs exercised after day 90 automatically convert to NSOs and lose their preferential treatment.

This creates a real financial squeeze at private companies. You may need substantial cash to exercise within 90 days, and there’s no liquid market to sell shares and offset the cost. Some companies have started offering extended post-termination exercise windows of one to ten years, but the ISO-to-NSO conversion after 90 days still applies.

Early Exercise and the 83(b) Election

Some companies, particularly startups, let you exercise options before they vest. This is called early exercise, and it exists for one reason: to start the clock on long-term capital gains treatment as early as possible. When you early-exercise, you buy shares that the company can claw back if you leave before they vest. Those unvested shares are considered restricted property.

Early exercise only makes tax sense if you file an 83(b) election with the IRS. The election tells the IRS you want to recognize income now, at the time of transfer, based on the current spread between fair market value and what you paid.⁹ At a startup where the strike price equals fair market value, that spread is zero, so your taxable income is zero. From there, all appreciation qualifies for capital gains treatment once you meet the applicable holding periods.

The deadline is absolute. You must file the 83(b) election within 30 days of receiving the shares.⁹ No extensions, no exceptions. Miss it by a single day and the election is gone permanently. Send it by certified mail so you have proof of the postmark. The risk is that if you leave the company and forfeit unvested shares, you lose the money you spent exercising them and cannot claim a deduction for the forfeiture.

Section 409A and Underpriced Strike Prices

Stock options must be granted with an exercise price at or above the stock’s fair market value on the grant date. Get this wrong and the options fall under Section 409A’s deferred compensation rules, which impose a 20% additional tax on the option holder plus interest calculated from the year the options vested.¹⁰ The penalty falls on you as the option holder, not on the company.

For public companies, fair market value is easy to establish from the trading price. Private companies rely on a formal appraisal, commonly called a 409A valuation, typically updated at least annually or after major events like a funding round. If you’re joining a startup, the valuation date matters, because a grant issued right before a new funding round might lock in a significantly lower strike price than one issued right after.

Deferral for Private Company Employees

Employees at private companies face a unique problem: they owe tax on option exercises even though there’s no public market where they can sell shares to cover the bill. Section 83(i) addresses this by allowing eligible employees of private companies to defer the income from exercising stock options for up to five years from the date the stock vests.⁹

The eligibility requirements are narrow. The company’s stock cannot be publicly traded on an established market. The company must grant options to at least 80% of its U.S. employees under a written plan. And several categories of employees are excluded entirely: anyone who owns 1% or more of the company, the CEO, the CFO, the four highest-compensated officers, and family members of any of these individuals.

The deferral ends at the earliest of five events: the stock becomes transferable, you become an excluded employee, the company goes public, five years pass from the vesting date, or you revoke the election. One trap worth knowing: the tax owed is calculated based on the stock’s value at the time you made the election, not the value when the deferral ends. If the stock drops during the deferral period, you still owe tax on the original higher amount.

1
Office of the Law Revision Counsel. 26 U.S.C. 422 – Incentive Stock Options
2
eCFR. 26 CFR 1.422-4
3
Internal Revenue Service. Announcement 2002-108
4
Internal Revenue Service. Topic No. 427, Stock Options
5
Office of the Law Revision Counsel. 26 U.S.C. 421 – General Rules
6
Internal Revenue Service. Instructions for Form 6251
7
Internal Revenue Service. Form 6251 – Alternative Minimum Tax, Individuals
8
Office of the Law Revision Counsel. 26 U.S.C. 53 – Credit for Prior Year Minimum Tax Liability
9
Office of the Law Revision Counsel. 26 U.S.C. 83 – Property Transferred in Connection With Performance of Services
10
Office of the Law Revision Counsel. 26 U.S.C. 409A – Inclusion in Gross Income of Deferred Compensation Under Nonqualified Deferred Compensation Plans