The deadline to file a 2021 return for a refund is today, April 15, 2025.
The due date for filing an original return to claim a refund is three years from the return's original due date. Filing an automatic 6-month extension does not extend the refund expiration date.
The reference to "3 years before you filed the claim plus any extension of time you had to file you return" above is related to the amount of refund you can claim, not the deadline to claim the refund.
You and the IRS can agree in writing to extend the deadline, but this usually happens if you're being audited for a return you actually filed and the IRS needs more time to complete the audit.
