What Is Form 3921? Definition, How It Works and Examples

Form 3921 reports one event: an employee exercised an ISO. An ISO is a stock option that gets special tax treatment. You generally owe no regular income tax when you exercise it. The IRS still wants a record of the exercise, so the company files a copy of the form with the IRS and gives you one. The IRS instructions require a separate form for each transfer of shares.

The form has two jobs for you. First, it supports the alternative minimum tax (AMT), a second tax calculation that can apply in the year you exercise. Second, it shows the dates and values you need when you later sell the shares. The IRS says these figures help you work out your capital and ordinary income. See how to exercise stock options for the steps before the form arrives.

The form covers ISOs only. A non-qualified stock option has no Form 3921, because its spread is taxed as income at exercise. A similar form, Form 3922, covers purchases under an employee stock purchase plan. Our page on ISO vs NSO explains the difference between the two option types.

The form has six numbered boxes. It also carries the company’s details and your name, address and taxpayer identification number.

The fair market value in box 4 is the price a willing buyer would pay on the exercise date. A private company has no stock exchange price, so the company sets this value, often with an outside appraisal. See 409A valuation for how that appraisal works.

It is a short statement and carries no tax calculation. Near the top you find the company that transferred the stock and your own details. Below that sit boxes 1 through 6, filled with dates, dollar amounts and a share count. There are no calculations on it and no line that says how much tax you owe.

Whatever the format, it should show the same boxes. Check each date and dollar figure against your option agreement and exercise confirmation. A wrong date in box 1 or 2 can change whether a later sale qualifies for the better tax treatment.

The company that transfers the stock files the form. That includes related companies and agents who handle the share transfer for it. A company need not send a form to a nonresident alien employee who was not required to receive a Form W-2 for the period from the grant year through the exercise year.

If you exercised in 2026, the form is due to you in early 2027 under the same January 31 rule. If it does not arrive, ask your stock plan administrator or your company’s finance team. The IRS gets its copy from the company, so you do not file one yourself.

An employee at a private company exercises 10,000 ISOs in 2026. The options were granted on March 3, 2024 with an exercise price of $1.50. On the exercise date of June 10, 2026, the company’s appraisal sets the share value at $8.

There is no regular income tax on the $65,000 spread in 2026. For AMT, the spread is generally an adjustment in the year of exercise, which can raise the AMT bill. The employee’s basis for regular tax is the $15,000 paid. The two years from the grant date ended on March 3, 2026, so a sale after June 10, 2027 would meet both holding periods and the gain would be taxed as a capital gain. A sale sooner is a disqualifying disposition, and the IRS then treats part of the profit as ordinary income. See AMT and cost basis for how those two numbers carry forward.

• Ignoring it because no tax was dueThere may be no regular tax at exercise, but the AMT can apply. The spread is the number to check.
• Waiting for a form that never comesIf you exercised and nothing arrived by February, ask the company. A missing form does not remove the exercise from your records.
• Not matching the form to your own recordsA wrong date or share count can change your holding periods and your basis. Compare the form with your exercise confirmation.
• Expecting a form for every option typeForm 3921 covers ISOs only. Non-qualified options and RSUs are taxed as income instead.
• Selling too soonA sale within two years of the grant or one year of the exercise turns part of the gain into ordinary income.

Form 3921

The IRS statement a company files and sends to an employee after an incentive stock option exercise.

Incentive stock option (ISO)

A stock option that can avoid regular income tax at exercise if holding periods and other rules are met.

Exercise price

The price per share you pay to buy shares under the option.

Fair market value

The price a willing buyer and seller would agree on. For a private company, an appraisal usually sets it.

Spread

The gap between the fair market value and the exercise price, per share.

Alternative minimum tax (AMT)

A second tax calculation that can apply to the spread in the year of an ISO exercise.

Disqualifying disposition

A sale before the ISO holding periods are met. Part of the profit is then taxed as ordinary income.

Figures were last checked on October 13, 2026. Rules are US federal. Due dates and penalties are for the 2026 filing season, which covers exercises made in 2025. The worked example is illustrative arithmetic. State taxes are not covered.