If you exercised an Incentive Stock Option (ISO), you may receive Form 3921, Exercise of an Incentive Stock Option Under Section 422(b). While receiving this form doesn't always mean you'll owe tax, it contains important information you'll need for future tax reporting.
In most cases, exercising an ISO by itself does not create regular taxable income. However, the exercise may affect your Alternative Minimum Tax (AMT) calculation and should be retained with your tax records.
What Is Form 3921?
Form 3921 reports information about the exercise of an Incentive Stock Option, including:
- The date the option was granted
- The date the option was exercised
- The exercise price paid for the stock
- The fair market value of the stock on the exercise date
- The number of shares acquired
This information helps determine whether an AMT adjustment is required and may also be needed when the stock is eventually sold.
Do I Owe Tax When I Exercise an ISO?
Generally, no regular income is recognized when you exercise an Incentive Stock Option.
However, if your return is subject to the Alternative Minimum Tax (AMT), you may need to include an adjustment based on the difference between:
- The fair market value of the stock on the exercise date, and
- The amount you paid to acquire the stock.
This difference is often referred to as the ISO "spread" and becomes part of the stock's AMT basis.
What If I Sold the Stock in the Same Year I Exercised the Option?
If you exercised and sold the stock during the same tax year, an AMT adjustment is generally not required.
Instead, the sale is reported in the year of disposition, and the gain or loss is calculated using the appropriate basis and holding-period rules.
Do I Need to Enter Form 3921 in My Tax Return?
Not necessarily.
Form 3921 is primarily an informational document. Many taxpayers do not directly enter the form into their return unless it affects an AMT calculation or the stock was sold during the tax year.
The information reported on Form 3921 should be kept with your tax records and used when determining the gain or loss on a future sale of the stock.
Why Should I Keep Form 3921?
Keep Form 3921 for your records because you'll need it when the stock is sold or otherwise disposed of in a future year.
The information reported on the form can help you:
- Determine your cost basis.
- Calculate any gain or loss from the sale.
- Calculate any AMT-related adjustments.
- Ensure the sale is reported accurately on your tax return.
Failing to keep Form 3921 may make it more difficult to accurately calculate the taxable gain or loss when you eventually sell the shares.
Before You File
If you exercised an Incentive Stock Option during 2026, review whether an Alternative Minimum Tax adjustment may apply to your return. If you continue to hold the shares after the exercise, keep Form 3921 with your permanent tax records so it will be available when you sell the stock in a future tax year.