When an employee exercises an incentive stock option, the company has a reporting obligation to both the employee and the tax authority.
The information required is simple in principle and awkward in practice for a private company, because it depends on values at specific dates that have to have been established at the time rather than estimated afterwards.
This covers what an exercise is, who has to report it, what information the form carries, why it matters to the employee's own position, and the records a company should be keeping as grants and exercises happen.
Corporations that grant incentive stock options (ISOs) to employees must file Form 3921 every year an employee exercises an ISO. This information return tells the IRS about the exercise price, the fair market value at exercise, and the number of shares acquired. Employees use Form 3921 to calculate their alternative minimum tax (AMT) exposure. Here is everything a corporation needs to know to file correctly.
What Is an ISO Exercise?
An ISO is a type of employee stock option that receives favorable tax treatment. When an employee exercises an ISO (buys shares at the grant price), there is no regular income tax at the time of exercise. However, the spread between the exercise price and the fair market value on the exercise date is an AMT preference item for the employee.
Companies that keep their cap table current find this reporting trivial. Companies that reconstruct it from board consents and emails at the year end find it slow, and the errors land on employees' personal returns, which costs goodwill as well as time.
Ankit Sarawagi, CPA, CA, MBA · LinkedInWho Must File Form 3921?
Any corporation that transfers shares to an employee upon exercise of an ISO must file Form 3921 for each exercise during the calendar year. If the same employee exercises multiple ISOs during the year, a separate Form 3921 is required for each exercise.
What Information Goes on Form 3921?
| Box | Information Required |
|---|---|
| Payer (corporation) | Corporation name, address, and EIN |
| Recipient (employee) | Employee name, address, and SSN |
| Box 1, Date of grant | The date the ISO was originally granted to the employee |
| Box 2, Date exercised | The date the employee exercised the option |
| Box 3, Exercise price per share | The price per share the employee paid (strike price) |
| Box 4, FMV per share on exercise date | Fair market value of one share on the exercise date |
| Box 5, Number of shares transferred | Total number of shares acquired in this exercise |
Filing Deadlines
| Filing Method | Deadline |
|---|---|
| Copy B to employee (recipient) | January 31 of the year following the exercise |
| Copy A to IRS, paper | February 28 of the year following the exercise |
| Copy A to IRS, electronic (e-file) | March 31 of the year following the exercise |
Pro Tip: If you are filing more than 10 information returns (counting all types: W-2, 1099, 3921, etc.) for the year, you are required to e-file beginning with tax year 2023.
Employee AMT Implications
Employees use Form 3921 to calculate the ISO adjustment for the alternative minimum tax. The AMT preference is the difference between Box 4 (FMV) and Box 3 (exercise price), multiplied by Box 5 (shares). If the employee holds the shares for a qualifying period (more than 2 years from grant date AND more than 1 year from exercise date), any sale profit is taxed as long-term capital gain.
If the holding period requirements are NOT met (disqualifying disposition), the spread at exercise becomes ordinary income in the year of sale, the employer may need to issue a corrected or supplemental W-2.
Recordkeeping for ISO Grants
- Keep ISO grant agreements documenting the grant date, number of shares, and exercise price
- Maintain stock ledger records of all ISO exercises
- Document the FMV calculation method used at each exercise date (409A valuation, market price for public companies)
- Track holding periods to identify qualifying vs disqualifying dispositions
Correcting Form 3921
If you need to correct a filed Form 3921 (wrong FMV, wrong number of shares, wrong dates), prepare a corrected form with the 'Corrected' box checked, file the corrected Copy A with the IRS, and send the corrected Copy B to the employee.
Book a free consultation and we will take the return off your desk.
Frequently Asked Questions
Do S-corporations file Form 3921?
S-corporations cannot grant ISOs (by definition, ISO rules require a C-corporation). S-corporation stock options are typically non-qualified stock options (NSOs), not ISOs. Form 3921 applies only to C-corporations granting ISOs.
What if we did not track FMV at the exercise date for a private company?
You need to determine FMV retroactively using a reasonable method. For private companies, FMV is typically established through a 409A valuation. The IRS expects reasonable, documented FMV for all stock option exercises.
Is there a penalty for not filing Form 3921?
Yes. Penalties are the same as for other information returns, $60 to $310 per form depending on how late the filing is, with a maximum of $630+ for intentional disregard.
What should a company track through the year to make this straightforward?
Each grant, each exercise, the dates of both, the number of shares and the relevant values at each point. Companies that maintain this in a cap table system find the reporting trivial. Companies that reconstruct it from board consents and emails at the year end find it slow, and errors here reach employees' personal returns, which makes them expensive in goodwill as well as in time.
Does the employee have to do anything with the copy they receive?
Keep it, and give it to whoever prepares their return. It does not by itself create a payment obligation at exercise, but it records figures that affect their position both in that year and when the shares are eventually sold. Employees who discard it commonly find the sale year harder to compute than it needed to be.
Written by
Ankit Sarawagi, CPA, CA, MBA
Ankit leads the finance team at Profitjets, where he has worked with 500+ businesses across the US on bookkeeping, tax and CFO-level strategy. He writes about the habits that keep small business books accurate all year. Connect on LinkedIn
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