California Code, Revenue and Taxation Code - RTC § 60511

Interest shall be paid upon any refund of tax at the modified adjusted rate per month established pursuant to Section 6591.5 from the first day of the calendar month following the day a properly completed claim for refund was received by the board on any claim that has not been paid within 20 calendar days of the receipt of a properly completed claim form by the board.

The interest shall be paid to the last day of the month following the date upon which the claim is approved by the board.

No interest shall be granted on credits taken on tax returns.