Incentive Stock Options: When to Exercise, What It Costs, and How to Plan

Few things feel better than seeing the words "stock options" in a job offer. Few things feel worse than a tax bill on stock you haven't even sold yet. Incentive stock options, or ISOs, can deliver both, sometimes in the same year. The difference usually comes down to timing: when you exercise, how much you exercise, and how long you hold. Let's break down how ISOs work, how they're taxed, and how to make a plan before the IRS makes one for you.

First, what is an ISO?

An incentive stock option gives you the right, but not the obligation, to buy a set number of shares of your company's stock at a fixed price, called the strike or exercise price. That price is locked in on the day the options are granted. Like RSUs, options usually vest over time, and you can only exercise the ones that have vested.

What makes an ISO special is its tax treatment. Handled correctly, the entire gain can end up taxed at long term capital gains rates instead of ordinary income rates.¹ Handled carelessly, it can generate a tax bill on money you never actually received. More on that shortly.

Is it even worth exercising?

Before taxes enter the picture, start with a simple question: is the stock trading above your strike price?

If your strike price is $10 and the stock is trading at $8, exercising makes no sense. You would be paying $10 for something anyone can buy on the open market for $8. Think of it like a coupon for a $10 burger when the burger is on the menu for $8. Nobody hands over the coupon to pay more. In the finance world these options are called "underwater," and the right move is usually to wait.

When the stock is above your strike price, the options are "in the money." If the stock is at $30 and your strike is $10, each option has $20 of value built in. That difference is called the spread, and it's where all the value, and all the tax questions, live.

Two dates matter no matter what the stock is doing:

• Expiration. ISOs generally must be exercised within 10 years of the grant date, and many plans set a shorter term.⁵ Options that expire unused are worth nothing.
• Leaving your job. If you leave, you typically have only three months to exercise and keep ISO tax treatment.² Some plans cut you off even sooner.

Taxes, part one: exercising is tax free, mostly

When you exercise an ISO, you generally owe no regular income tax. No W2 income, no withholding, nothing.¹ Sounds great, right?

Here is the catch. The spread at exercise counts as income for the alternative minimum tax, the parallel tax system that exists mostly to keep tax preparers humble.^1,3 If the spread is big enough, it can push you into AMT and create a real tax bill in April, even though you haven't sold a single share.

For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, and it starts to phase out at $500,000 of income for singles and $1,000,000 for joint filers.⁴ Income above the exemption is taxed at AMT rates of 26% and 28%.³ Whether you owe anything depends on how your regular tax compares to your AMT, which is why this is a "run the numbers first" decision.

The good news: AMT paid because of an ISO exercise is often recoverable later as a credit against your regular tax, claimed on Form 8801.⁶ The bad news: "later" can mean several years.

Taxes, part two: when you sell

This is where the holding period rules come in, and they decide whether your gain gets the good tax treatment or the ordinary one.

• Qualifying disposition. Hold the shares at least 2 years from the grant date and at least 1 year from the exercise date. Do that, and your entire gain above the strike price is taxed as a long term capital gain.²
• Disqualifying disposition. Sell before meeting both holding periods, and the spread at exercise gets taxed as ordinary income, generally limited to your actual gain if the stock has dropped. Anything above that is a capital gain.²

Let's put numbers on it. Say you exercise 5,000 options with a $10 strike when the stock is at $30. It costs you $50,000 to exercise, and your spread is $100,000.

• Hold for the qualifying period and sell at $40: Your $150,000 gain is all long term capital gain.
• Sell right away at $30: The $100,000 spread is ordinary income, just like a bonus.
• Hold, and the stock falls to $12 the following year: This is the one that keeps people up at night. Your AMT is based on the $100,000 spread on the day you exercised, so you could owe tax on that full amount. Meanwhile, your shares are now worth $60,000, only $10,000 more than the $50,000 you paid. In plain English, you could owe tax on $100,000 of profit you will never actually see. Plenty of tech employees learned this the hard way when stocks crashed in 2000.

Your employer will send you Form 3921 for each year you exercise.⁷ It lists the grant date, exercise date, strike price, and market value at exercise. Keep every one of them. Your cost basis for regular tax and for AMT can be different numbers, and your future self (and your tax preparer) will need both.

How to plan your exercise

Exercise in bite sized pieces. Rather than exercising everything at once, many people exercise just enough each year to stay under the point where AMT kicks in. Over several years, that can move a lot of options into the long term capital gains lane with little or no AMT.

Exercise early in the year. If you exercise in January and the stock tanks by November, you can sell those shares before December 31. A sale in the same calendar year wipes out the AMT adjustment, because regular tax and AMT treat the sale the same way.³ You would owe ordinary income tax on the (smaller) gain, but you dodge the phantom income problem. Exercise in December and you lose that escape hatch.

Know the $100,000 rule. Only $100,000 worth of ISOs, measured by the stock value at grant, can first become exercisable in any one calendar year. Anything above that is automatically treated as a nonqualified stock option, which is taxed as ordinary income at exercise.⁵ Big grants and accelerated vesting are where this sneaks up on people.

Consider the exercise and sell. Sometimes the simplest move is the right one. Exercising and selling the same day gives up the capital gains treatment, but it also gives up the risk. If company stock is already a big chunk of your net worth, locking in the gain can be worth more than the tax savings. Our article on concentrated positions goes deeper on this.

Mind the calendar if you are leaving. Changing jobs? Retiring? Being acquired? Find out your post termination exercise window before your last day, not after. Three months sounds like plenty of time, right up until you are learning a new job, a new commute, and a new benefits portal all at once.

The bottom line

ISOs can be one of the most valuable parts of your compensation, but the value depends on the stock price, the calendar, and how you exercise. When the options are in the money, the question becomes when to exercise, how much, and how long to hold, and the tax answer can swing by tens of thousands of dollars. At Swan Wealth we model your exercise alongside your income, AMT exposure, and overall portfolio so you get the most out of your options without an April surprise. If you have ISOs vesting, expiring, or you are about to change jobs, give us a call.

This is general education, not personalized tax or investment advice. Examples are hypothetical and simplified, and ignore state taxes. How and when to exercise depends on your grant terms, income, and the rest of your portfolio, so let's look at your numbers before you exercise.

Sources

1. IRS, "Topic no. 427, Stock options": no income when an ISO is granted or exercised, possible alternative minimum tax in the year of exercise, and special holding period requirements for capital gain treatment. irs.gov/taxtopics/tc427
2. IRS, Publication 525, "Taxable and Nontaxable Income," Incentive Stock Options section: holding periods of 2 years from grant and 1 year from exercise, ordinary income on a disqualifying disposition, and the requirement to exercise within 3 months after leaving employment. irs.gov/publications/p525
3. IRS, "Instructions for Form 6251, Alternative Minimum Tax, Individuals": ISO adjustment on line 2i, no adjustment required when stock is acquired and disposed of in the same year, and the 26% and 28% AMT rates. irs.gov/instructions/i6251
4. IRS, "IRS releases tax inflation adjustments for tax year 2026, including amendments from the One, Big, Beautiful Bill": 2026 AMT exemption of $90,100 single and $140,200 married filing jointly, phasing out at $500,000 and $1,000,000. irs.gov/newsroom
5. 26 U.S.C. § 422, "Incentive stock options": 10 year maximum option term and the $100,000 per year limitation. uscode.house.gov
6. IRS, "About Form 8801, Credit for Prior Year Minimum Tax." irs.gov/forms-pubs/about-form-8801
7. IRS, "About Form 3921, Exercise of an Incentive Stock Option Under Section 422(b)." irs.gov/forms-pubs/about-form-3921