Financial Glossary
Form 3921
Form 3921 is an IRS information return that employers must file and furnish to employees each time an employee exercises an incentive stock option. It reports the exercise date, the fair market value of the stock on the exercise date, the exercise price paid, and the number of shares acquired. The form provides the data employees need to calculate potential alternative minimum tax exposure and establish their cost basis for future sale. Employers who fail to file or furnish Form 3921 by the required deadlines face per-form penalties that compound with volume.
Problem & Application
A startup with 40 employees has 12 option holders who exercise ISOs in the same calendar year. Each exercise is a separate reportable event requiring its own Form 3921. The company's HR software tracks option grants but does not automatically generate the IRS filing. A bookkeeper manually compiles the data: grant date, exercise date, fair market value per share on exercise date (using the most recent 409A valuation), exercise price, and share count. If the 409A valuation is stale -- more than 12 months old -- the fair market value figure becomes legally unreliable and can expose both the company and the employee to IRS scrutiny. Filing accurate, timely Form 3921s also helps employees plan whether to hold shares through the ISO qualifying disposition period or sell immediately, a decision with meaningful personal tax consequences.
In Short
Form 3921 ensures that ISOs are reported correctly for tax purposes, which helps avoid penalties and supports employee compliance.