Cal. Gov. Code § 21033
A member electing to receive credit for public service shall contribute in a lump sum or by installment payments over that period and subject to minimum payments as may be prescribed by regulations of the board an amount equal to (a) the contributions he or she would have made to this system for the period for which current service credit is granted, assuming that the rate of contribution under his or her employer's formula at the rate age applicable to him or her at the beginning of his or her first subsequent period of service in membership and his or her compensation earnable on that date had applied to him or her during the period for which credit is granted, plus (b) the added contribution that may be specially required under this article as a condition for crediting particular public service, plus (c) the interest which would have accrued to those contributions if they had been deposited at the beginning date of his or her first subsequent period of service in membership, from that date until the date of completion of payments, and (d) if he or she elects to contribute in other than one sum, interest on the unpaid balance of the amount payable to the retirement fund, beginning on the date of the election to receive credit. The beginning date of the first subsequent period of service for purposes of computation of contribution and interest shall be deemed to be the end of the period of service credited for a member who has no subsequent return to service. For a member who is subject to Section 21076 or 21076.5, and Section 21077, the service and contribution rate to be used for purposes of computation shall be deemed to be the service and contribution rate that would have been used had the member not been subject to Section 21076 or 21076.5, and Section 21077.
Ca. Gov. Code § 21033