ISOs vs NSOs: how stock options are taxed before they fund your early retirement

By Tom, CPA · Updated October 25, 2026

TL;DR: NSOs create ordinary wage income at exercise, equal to the spread between market value and strike price. ISOs create no regular tax at exercise, but the spread counts for AMT. If ISO shares are held more than 2 years from grant and 1 year from exercise, the whole gain is long-term capital gain; sell sooner and part of it becomes ordinary income. Basis reporting on Form 1099-B often needs fixing.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

Stock options are the startup world's version of a lottery ticket that comes with homework. Lavish Larry exercised a pile of ISOs in December, felt rich, and learned about the alternative minimum tax in April. Frugal Fran read Form 3921 first and slept fine. For FIRE seekers at growing companies, options can be the single biggest accelerant, or the single biggest way to owe tax on money that evaporated.

This guide covers federal tax treatment as of Oct 2026, drawing on IRS Topic 427 and Publication 525. State tax rules vary. Restricted stock units are a different animal, covered in the RSU and ESPP guide.

CPA Warning Label: Exercising options can create a tax bill on paper gains you can't spend. If the stock drops before you sell, the tax from exercise may not go away.

NSO tax at exercise

Nonqualified (non-statutory) stock options, or NSOs, are the default kind. They can be granted to employees, contractors and directors.

• At grant: generally no tax, because most options don't have a readily determinable fair market value.
• At exercise: the spread, meaning fair market value at exercise minus the price you pay, is compensation income. For employees it's wages, included on Form W-2 (box 12, code V) and subject to income tax withholding, Social Security and Medicare.
• At sale: your basis is the price you paid plus the income you recognized. Further gain or loss is capital, long-term if you held the shares more than one year after exercise.

Withholding on supplemental wages is often a flat rate that can be lower than your actual marginal bracket. A large NSO exercise in a high-income year can leave you under-withheld. Plan an estimated payment or extra withholding.

Brokerage Form 1099-B basis is a common trap. For options granted in 2014 or later, the reported basis generally doesn't include the compensation income already on your W-2. If you don't adjust it on Form 8949, you can pay tax twice on the same spread.

ISO and AMT

Incentive stock options (ISOs) are statutory options available only to employees. You must be an employee of the granting company (or a related company) from grant until at least 3 months before exercise, with exceptions for disability and death.

• At grant and at exercise: no regular income tax. Your employer reports the exercise on Form 3921.
• But for AMT: the spread at exercise is an adjustment for the alternative minimum tax, reported on Form 6251, if you hold the shares past the end of the calendar year of exercise.

AMT is a parallel tax system. You compute tax both ways and pay the higher amount. As of tax year 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, and it begins to phase out at AMT income of $500,000 and $1,000,000 respectively (IRS Rev. Proc. 2025-32). A large ISO spread can easily push someone over the exemption.

The silver lining is that AMT paid because of ISO exercises often generates a minimum tax credit that can be used in later years when regular tax exceeds AMT. That can be useful in early retirement, when your regular tax may be low. But it isn't instant, and in some years it isn't usable at all.

Exercising and selling ISO shares in the same calendar year generally avoids the AMT adjustment, but it turns the spread into ordinary income (see below).

Qualifying dispositions

To get the full ISO benefit, you must hold the shares more than 2 years after the grant date AND more than 1 year after the exercise date. Then:

• The entire gain, sale price minus exercise price, is long-term capital gain.
• Nothing is ordinary income.

If you sell earlier, it's a disqualifying disposition:

• The lesser of the spread at exercise or the actual gain is generally ordinary compensation income.
• Any additional gain is capital gain, short- or long-term depending on how long you held the shares after exercise.

For FIRE planners, the 2-year/1-year clock collides with concentration risk. Holding a single stock for a year to save taxes only works if the stock doesn't fall more than the tax savings.

Early exercise and 83(b)

Some companies let you exercise options before they vest, receiving restricted stock that vests over time. Normally, restricted property is taxed when it vests, at its value then (Pub 525). A Section 83(b) election lets you instead include the value in income at the time you receive the restricted stock.

• The election must be filed with the IRS within 30 days after the property is transferred. There are no extensions. The IRS has released Form 15620 for making the election.
• 83(b) applies to restricted stock, not to options themselves.
• If you early exercise when the strike equals fair market value, the income you recognize can be close to zero, which starts the capital gain clock early.
• For ISOs, an early exercise with an 83(b) election can also limit the AMT spread.
• Risk: if you leave before vesting and forfeit the shares, or the company fails, you generally can't deduct the income you elected to recognize.

There's also a separate Section 83(i) election that lets certain employees of eligible private companies defer income from qualified equity grants. It's narrow and has many conditions.

Example

Illustration: Fran holds 10,000 options with a $5 strike. The stock is worth $25 when she exercises, a $200,000 spread, and she sells two years later at $40.

Now the worst case: an ISO holder exercises in year 1 at $25 and holds. The stock falls to $6 by the following April. The $200,000 AMT adjustment for year 1 still stands. A sale in year 2 creates a loss for regular tax, but the AMT from year 1 is already owed. This scenario has a long and painful history.

Planning moves people use

• Exercise ISOs in small annual tranches sized to stay under the AMT crossover point, which tax software can estimate by running the return with and without the exercise.
• Exercise early in the calendar year so that, if the stock drops, you can still choose a disqualifying sale before December 31. That converts the AMT problem into ordinary income measured at the lower sale price.
• Exercise NSOs in lower-income years, such as a sabbatical or the first year of early retirement, if the options remain exercisable after you leave. Many plans give departing employees only a short window, often 90 days, so read the plan document.
• Set cash aside for the exercise cost and the tax, so you aren't forced to sell other investments at a bad time.

FIRE takeaways: model exercises across several tax years, use low-income years for exercises when possible, and diversify. Fold the proceeds into your portfolio review and check what the resulting portfolio supports with the withdrawal rate calculator.