If I will be receiving a refund from state of California, what is the deadline to file or request an extension?

California State Income Tax Return (Due Date April 18, 2022).  If you cannot file your return by the April 18th deadline, then you should request an extension.

California gives you four years from the due date of the original return to file for a refund.  So for tax year 2021 you would have until April 15, 2026 to file for refund.

If you file for an extension for tax year 2021 the extension request must be filed on or before April 18, 2022