California Code, Revenue and Taxation Code - RTC § 12301

(a) The taxes imposed upon insurers by Section 28 of Article XIII of the California Constitution and this part, except with respect to taxes on ocean marine insurance and retaliatory taxes, are due and payable annually on or before April 1 of the year following the calendar year in which the insurer engaged in the business of insurance or transacted insurance in this state. The taxes imposed with respect to ocean marine insurance are due and payable on or before June 15 of that year.

(b) This section shall become operative on July 1, 2013.