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When an employee exercises an incentive stock option, the company picks up a new filing obligation: Form 3921.
The form gives the IRS a record of the exercise, the grant date, the exercise date, what the employee paid, what the shares were worth, and how many shares changed ownership. Get the details or the deadlines wrong, and a good moment for an employee can turn into a costly one for the company.
This guide covers who must file Form 3921, what information it requires, the 2026 Form 3921 IRS deadlines, how to file through IRIS, and why the form matters to employees at tax time.
Form 3921 is an IRS information return that reports the transfer of stock to an employee who exercised an incentive stock option (ISO) under Section 422(b) of the Internal Revenue Code. It reports the exercise itself, not the grant or vesting.
The filing obligation starts the moment an employee exercises an ISO and receives shares. For each exercise, the form records:
Every ISO exercise counts, regardless of the size of the transaction, even a small number of shares can trigger a filing requirement. The company files Copy A with the IRS, gives Copy B to the employee, and keeps Copy C for its own records.
The two forms sound similar but cover different transactions.
Form 3921 reports the exercise of an ISO under Section 422(b), whether the employee sells the shares right away or holds onto them.
Form 3922 reports certain transfers of stock bought through an employee stock purchase plan (ESPP) under Section 423(c). ESPPs let employees buy shares through payroll deductions, often at a discount, and are a separate equity vehicle with its own rules.
A company running both an ISO plan and an ESPP may need to file both forms, sometimes for the same employee.
Any company that transfers stock to an employee under an ISO must file Form 3921. If your startup has granted ISOs to employees, you must ensure that this form has been completed correctly and is filed with the IRS when these options are exercised.
Filing Form 3921 is important because it allows the IRS to monitor ISO exercises accurately. Moreover, the IRS can ensure employees have correctly reported income from exercising these options on their tax returns. The employees can use the data from this form to accurately determine their taxable income from the ISOs.
An exception to filing Form 3921 applies if an employee is a non-resident alien (someone who does not live in the US and is not a US citizen). This exception applies only if you do not need to provide the employee a Form W-2 (a wage and tax statement) for any calendar year from the time the option is granted through the exercise date. In this case, filing Form 3921 for that specific exercise is not mandatory for you.
There are three different copies of the 3921 tax form, i.e., Copy A, Copy B, and Copy C. Each copy serves a different purpose and is intended for a different recipient.
Copy A: Form 3921 has to be filed with the IRS. This copy features all details related to the transaction, including the employee details, the stock option, and the exercise. You need to complete and submit this copy in a timely manner to avoid any probable penalties or legal issues.
Copy B: Must go to the employee who exercised the stock options. This copy serves as a record of the transaction and provides the data required to report income from the exercise of options on their tax return. You must distribute Copy B to the employees by January 31st of the following year. This allows them enough time to file their taxes.
Copy C: Should be kept in your company records. This helps you track the used stock options and the data shared with the IRS and the employees. It is recommended that you keep this copy for four years, the standard period for tax documents.
Form 3921 is short, but it leaves little room for creative interpretation. You will need:
Grant and exercise dates come from the option agreement and transaction records. The exercise price, sometimes called the strike price, is what the employee paid per share. The fair market value is what the share was worth on the exercise date, not the grant date.
For a private company, that fair market value is often set by a recent 409A valuation. A 409A valuation sets the strike price at grant; Form 3921 asks for the fair market value at exercise. Those two figures can differ if the company has grown between the two dates.
Here are the steps on how to correctly fill out and file Form 3921:
1. Get the form. You can download Form 3921 from the official IRS website
2. Fill it out completely. This includes details about the company, the employee, the ISO, and the exercise itself, the grant date, exercise date, exercise price, fair market value, and number of shares. Fill out every field carefully, since even a small error can create problems later.
3. File Copy A with the IRS. The deadline is generally the last day of February if you're filing on paper, or March 31 if you're filing electronically. You can file electronically through the IRS's newer system, IRIS, or by mail to the address listed in the IRS instructions. Check the exact date each year, since it shifts by a day or two whenever it falls on a weekend or holiday.
4. Get Copy B to the employee. The deadline is generally January 31, though it can move a day or two later if that date falls on a weekend or holiday. This gives the employee enough time to use the information when preparing their tax return.
5. Keep Copy C for your records. Good practice is to retain it, or make sure the underlying data can be reconstructed, for at least three years from the filing due date
6. Check whether electronic filing is required. If your company files 10 or more information returns in total during the year, counting W-2s, 1099s, and other forms like 3922 alongside your 3921s, electronic filing becomes mandatory, not optional. Even a small number of ISO exercises can trip this threshold once everything else is added in.
7. Set up electronic filing access early if needed. Electronic filing now goes through the IRS's IRIS system rather than the older FIRE system, which is being phased out. You'll need a Transmitter Control Code (TCC), a five-character ID that verifies your company's identity when filing. Apply well ahead of your deadline, since processing can take several weeks.
Failing to file Form 3921, or filing it with errors, can lead to penalties, so it's worth building in enough time to get the details and deadlines right.
There are specific deadlines to follow when filing Form 3921. Here are the standard dates each year:
1. January 31: This is the usual deadline for providing Copy B of Form 3921 to the employee who exercised the ISO. If this date falls on a weekend or holiday, it moves to the next business day.
2. February 28: (or 29 in a leap year), This is the usual deadline for filing Copy A of Form 3921 with the IRS if filing by paper. This copy must be submitted along with Form 1096, which serves as a transmittal form. Like the deadline above, this shifts to the next business day if it lands on a weekend or holiday.
3. March 31: This is the usual deadline for filing Form 3921 electronically. Note that this is different from what's sometimes quoted elsewhere as April 1, the correct standard date is March 31.
The company files Form 3921, but the numbers on it matter most to the employee. They use it to check for alternative minimum tax (AMT) exposure at exercise and to calculate cost basis when they eventually sell the shares.
The AMT-relevant figure is the spread between the fair market value at exercise and the exercise price. If an employee pays $2 a share for stock worth $12, the $10 difference per share can be an AMT adjustment, even though no cash changed ownership and no shares were sold.
That's why an ISO exercise can produce a tax bill with no matching liquidity. Employees generally use Form 6251 to work out AMT; Form 3921 supplies the inputs, not the final number. The result depends on the employee's broader tax picture, so a qualified tax adviser should be part of that conversation.
When the employee later sells the shares, the sale gets reported separately on Form 1099-B. The original exercise data determines the correct cost basis for that sale.
The IRS applies information-return penalties per form, so a small process failure can scale quickly across a large employee population.
File as soon as possible. Waiting does not make the missed deadline ; it only gives the penalty more room to grow. Filing within 30 days generally keeps the return in the lowest penalty tier.
If the late or incorrect filing resulted from reasonable cause rather than willful neglect, the IRS may waive the penalty. Relief is not automatic. The company generally needs to request it and document what happened, such as a natural disaster or a system failure, as well as the steps taken to correct the problem. Clear shared documentation can also make the correction process easier to support.
If you filed Form 3921 but later discover an error, submit a corrected form promptly and give the employee an updated copy. Do not wait for the employee to find the mismatch while preparing a tax return. Exercises by departing employees deserve the same review because an employee's exit does not erase a reportable exercise.
The best fix, of course, is the one you do not need. A reliable equity management workflow can flag exercises when they occur, preserve the supporting data and make year-end reconciliation considerably less theatrical.
Before filing, confirm that:
When a company gets acquired, ISOs often accelerate and a large batch of employees exercise within the same short window, sometimes right before the deal closes. Which triggers dozens of Form 3921s tied to a company that may be winding down or merging into another entity days later. If the filing gets lost in deal logistics, the acquiring company can inherit that reporting gap along with the cap table, and untangling it after close, once the original HR and equity teams have dispersed, is far harder than filing on time would have been. It's one of the few moments where a routine tax form and a company's biggest transaction collide, and it rarely gets attention until it's already a problem.
Qapita brings option grants, exercises, valuations, and cap table data into one place, so the numbers needed for Form 3921 are ready well before the deadline. See how Qapita keeps your equity records filing-ready. Book a demo
Not automatically. Form 3921 is an information return, not a tax bill. However, exercising an ISO can create an alternative minimum tax adjustment when the fair market value exceeds the exercise price. Employees should review the applicable ISO tax rules with a qualified tax adviser.
Yes. Form 3921 reports the exercise and transfer of shares, not their eventual sale. The company generally files it even when the employee continues to hold the shares. A later sale, including one connected to a cashless exercise, can create separate reporting obligations.
No. Form 3921 is specifically for incentive stock options that meet Section 422 requirements. NSOs have a different option tax treatment and may create wage reporting and withholding obligations when exercised.
Generally, yes. If an employee completes multiple ISO exercises during the calendar year, the company typically prepares a separate Form 3921 for each transfer of shares. This is why tracking each exercise as it happens is safer than trying to reconstruct the year from a single total.
If Copy B is missing, the employee should request another copy from the company. If the information is wrong, the company should prepare a corrected Form 3921 and provide the employee with the corrected statement. Employees should not silently adjust an incorrect equity statement without first asking the company to fix its filing.
