California Code, Revenue and Taxation Code - RTC § 12254

(a) The amount of each prepayment shall be 25 percent of the amount of the annual insurance tax liability reported on the return of the insurer for the preceding calendar year.

(b) In establishing the prepayment amount of an insurer that has acquired the business of another insurer, the amount of tax liability of the acquiring insurer reported for the preceding calendar year shall be deemed to include the amount of tax liability of the acquired insurer reported for that year.

(c) Notwithstanding subdivision (a), for a health insurer subject to Section 12202.2 both of the following shall apply:

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