California Code, Revenue and Taxation Code - RTC § 46502

(a) Except as provided in subdivision (b), no refund shall be approved by the board after three years from the due date of the payment for the period for which the overpayment was made, or, with respect to determinations made under Article 2 (commencing with Section 46201), Article 3 (commencing with Section 46251) or Article 4 (commencing with Section 46301) of Chapter 3, after six months from the date the determinations become final, or after six months from the date of overpayment, whichever period expires later, unless a claim therefor is filed with the board within that period. No credit shall be approved by the board after the expiration of that period, unless a claim for credit is filed with the board within that period or unless the credit relates to a period for which a waiver is given pursuant to Section 46205.

(b) A refund may be approved by the board for any period for which a waiver is given pursuant to Section 46205 if a claim therefor is filed with the board before the expiration of the period agreed upon.

(c) If the board has made a determination under Article 2 (commencing with Section 46201), Article 3 (commencing with Section 46251), or Article 4 (commencing with Section 46301) of Chapter 3, and if a person's claim for refund was filed timely within the applicable six-month period specified by subdivision (a) or (b), that claim for refund shall be deemed to also apply to that person's later payments in full or partial satisfaction of that determination.