Form 3921 instructions: A guide for US employees

Exercising incentive stock options can be exciting, but the paperwork may be less straightforward. If you exercised an incentive stock option, or ISO, your employer may send you Form 3921 early the following year.

So, what should you do with it? These Form 3921 instructions explain why you received the form, what each box means, and how the information may affect your alternative minimum tax and the tax you pay when you sell your shares.

We'll also introduce the Wise account, which allows you to send, spend, and receive your money across the globe in over 40 currencies – all at the fair mid-market rate.

Learn more 🔎

What is Form 3921?

Form 3921 is an IRS information return titled “Exercise of an Incentive Stock Option Under Section 422(b).” It records the transfer of company stock that happens when an employee exercises an ISO.¹

An ISO lets you buy employer stock at a fixed exercise price. The IRS generally doesn’t treat the difference between that price and the stock’s fair market value as regular taxable income when you exercise. However, the difference can count under the alternative minimum tax, or AMT, rules.²

The form provides the dates and values needed to evaluate AMT, tax basis, and your holding period. It applies to ISOs, not nonqualified options, restricted stock units, or shares bought through an employee stock purchase plan.²

Who files Form 3921?

Your employer, or another corporation involved in the stock transfer, generally files Form 3921 for each ISO exercise that transfers shares to you. If you exercised more than once during the year, you may receive more than one form.²

You’ll generally receive your copy early in the year after the exercise. For example, a 2025 exercise would be documented on a form sent in early 2026.²

You don’t send your copy back to the IRS. If you expected one but haven’t received it, contact your employer’s payroll, benefits, or stock plan administrator.

Form 3921 instructions: What each box means

First, check your name and taxpayer identification number. Your copy may show only the last four digits, although your employer reports the complete number to the IRS.¹

Box 1: Date option granted

This is the date your employer granted the ISO. It helps determine whether a later sale meets the special ISO holding-period requirements.

Box 2: Date option exercised

This is when you bought the shares. It starts part of the ISO holding-period test and identifies the year that may have an AMT adjustment.

Box 3: Exercise price per share

This is the amount you paid for each share. Multiply it by the number of shares in Box 5 to calculate the total exercise cost.

Box 4: Fair market value per share on exercise date

This is one share’s value when you exercised. The difference between Boxes 4 and 3 is the spread or bargain element and is generally relevant to AMT if you hold the shares beyond the exercise year.

Box 5: Number of shares transferred

This is the number of shares you acquired through that exercise. Use it with the per-share amounts in Boxes 3 and 4.

Box 6: Other corporation information

This identifies the corporation whose stock was transferred if it differs from the transferor named at the top. Otherwise, it may be blank.¹

How to use Form 3921 when filing your taxes

Compare the form with your stock plan records. If a date, share count, price, or value appears wrong, ask the issuer for a corrected form.

Next, determine whether the exercise affects AMT. It generally creates no regular federal income at exercise, but the spread can be included when calculating AMT.³

When the shares were transferable and not subject to a substantial risk of forfeiture at exercise, a basic spread calculation is:⁵

Suppose Form 3921 shows an exercise price of 10 USD in Box 3, a fair market value of 25 USD in Box 4, and 100 shares in Box 5. The potential AMT adjustment is 1,500 USD:

You generally report the adjustment on Form 6251 for the exercise year. This doesn't automatically mean you owe AMT, given that Form 6251 determines whether additional tax is due. ⁴

If you exercised and sold in the same calendar year, the spread is generally treated under the regular tax rules rather than as an AMT adjustment.

Share restrictions can change the calculation, so consider professional help when the spread is large, or the shares are private or restricted.²

Looking for smart ways to transfer money internationally? Let us introduce you to Wise

Send money to 140+ countries with the mid-market exchange rate and low, transparent fees with Wise. Set up a free Wise account online or in the Wise app, to transfer money fast in 40+ currencies.

Over 50% of Wise payments arrive instantly* — and all Wise transfers are deposited directly into your recipient's bank account for convenience.

No ongoing fees, no hidden charges and no hassle — just fast, transparent international transfers that can beat the banks.

Get started with Wise

*Transaction speed claimed depends on funds availability, approval by Wise’s proprietary verification system and systems availability of our partners’ banking system, and may not be available for all transactions.

What happens when you sell ISO shares?

Form 3921 becomes useful again when you sell the stock. The tax result depends in part on how long you held it.

To satisfy the ISO holding-period requirement, you generally must wait until the later of:

• One year after the shares were transferred to you, or
• Two years after the option was granted.²

A sale after both periods is generally a qualifying disposition. The difference between the sale proceeds and your regular tax basis (usually the exercise price plus certain costs) is generally treated as capital gain or loss.⁴

Selling earlier is generally a disqualifying disposition. Part of the result may be ordinary compensation income and the rest capital gain or loss. Your employer may report the compensation as wages on Form W-2.⁴

Basis needs attention. If a disqualifying disposition creates wage income, you generally add that income to the exercise cost when calculating basis. The figures reported by a broker may therefore need an adjustment on Form 8949.⁴

AMT creates a second basis calculation. If you include an ISO spread as an AMT adjustment, your AMT basis generally increases by that amount. Keep regular-tax and AMT records until sale. The difference can affect Form 6251 and may relate to an AMT credit.⁴

Common Form 3921 mistakes to avoid

• Ignoring the form because no tax was withheld: An ISO exercise may still affect AMT even when it produces no regular taxable income
• Attaching Form 3921 to Form 1040: It is normally a recordkeeping form, not a form the employee files with the return
• Assuming the 1099-B basis is complete: Stock-option basis may need an adjustment on Form 8949
• Losing track of dates: Boxes 1 and 2 help determine whether a sale is qualifying or disqualifying
• Combining separate exercises: Keep each Form 3921 and match the shares to the correct transaction when selling
• Forgetting state taxes: States may apply their own ISO and AMT rules, so federal treatment doesn’t answer every state-tax question

FAQs

Do I need to report Form 3921 on my tax return?

You generally don’t enter Form 3921 as a standalone item or attach it to Form 1040. However, its figures may be needed for Form 6251 in the year you exercise and for Form 8949 and Schedule D when you sell the shares.

What if I received Form 3921 but didn’t sell the stock?

You may still need to calculate an AMT adjustment for the exercise year. Keep the form even if no AMT is due because you’ll need the information when you later dispose of the shares.

What if I sold the shares in the same year I exercised?

When acquisition and disposition happen in the same year, the spread is generally handled under the regular tax rules instead of as an AMT adjustment. You must still report the sale correctly and determine whether it was a disqualifying disposition.²

Bottom line

Form 3921 can affect taxes in more than one year. Check it, calculate any potential AMT adjustment, and preserve its dates, prices, and share count until you sell. If the numbers are significant or the transactions are complicated, personalized advice can help prevent an expensive reporting mistake.

With Wise, you can send secure and trackable large amount transfers to 140+ countries worldwide with transparent fees and the fair mid-market exchange rate.

Have a look at the main benefits for using Wise to send large transfers:

• Dedicated support for large transfers
• Fast and easy setup with no physical paperwork
• Upfront, transparent fees
• Fully trackable transfers
• Fast transfer times
• Two-factor authentication and real-time notifications

🚀 Get started with Wise

Sources

1. IRS – Form 3921, including instructions for employees
2. Carta – Incentive Stock Options: How ISOs Work and Tax Treatment
3. Fidelity – Learn About Alternative Minimum Tax
4. Charles Schwab – ISO Taxes: A Guide
5. IRS – Publication 525, Taxable and Nontaxable: Income

Sources checked 09/28/2026