Cost basis, Form 3921 and Form 3922
These two information returns carry the numbers you need to compute basis on option and ESPP shares.
Form 3921
Issued after an ISO exercise, it reports the strike price, fair market value at exercise and share count — the inputs for your AMT adjustment and dual cost basis.
Form 3922
Issued for ESPP share transfers, it provides the offering date price, purchase date price and actual purchase price needed to split ordinary income from capital gain.
Keep them forever
You may sell those shares years later. Without these forms the basis calculation becomes guesswork and usually resolves in the IRS's favour.
Educational content, not tax advice. Your outcome depends on your grant documents, income and state. Equity Tax Engine models your actual position — join the waitlist.