For Federal Taxes:
The tax return for your income earned in 2019 was due in April 2020, has a 3 year deadline, so It must be filed by April 2023.
The tax return for the income earned in 2020 was due in April 2021, has a 3 year deadline, so it must be filed by April 2024.
And so forth.
If you fail to file by the three year deadline, you will not be able to get a refund. If you owe them money, they may already be looking for you, end interest and penalties may be piling up. It is also possible to be in an in-between condition where they have enough information to know you should have filed, and they think you owe them money, but in reality you are due a refund because of things they don't currently have in their records.
For California:
Statute of limitations
SOL is a time limit imposed by law on the right of taxpayers to file a
claim for refund.
Generally, you must file your claim for refund by the later of:
- 1 year from the date of overpayment
- 4 years after the original return due date.
If you filed before the due date, you have 4 years from the original return due date to file a claim.
- If you filed after the extension, the return is late. You have 4 years from the original return due date to file a claim.
- If you made payments and never filed a tax return, you have 4 years from the original return due date to file a claim.
- 4 years after the date of a timely filed return, if filed within the extension period.
Note on Federal deadlines: they changed during the health crisis, Most years the deadline is in April but 2020 and 2021 were different.