Cal. Rev. & Tax. Code § 19107

Where an overpayment is made by any individual for any year, and a deficiency is owing from the spouse of the taxpayer for the same year, and both spouses notify the Franchise Tax Board in writing prior to the expiration of the time within which credit for the overpayment may be allowed that the overpayment may be credited against the deficiency, no interest shall be assessed on that portion of the deficiency as is extinguished by the credit for the period of time subsequent to the date the overpayment was made.