Cal. Government Code § 21051

(a) A member electing to receive credit for service subject to this section shall contribute, in accordance with Section 21050, an amount equal to the following: (1) The contributions the member would have made to the 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 the member during the period for which credit is granted. (2) The interest that would have accrued on 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. (3) If the member is authorized under Section 21050 to contribute in other than a lump-sum payment, interest on the unpaid balance of the amounts payable under paragraphs (1) and (2), which interest shall begin to accrue as of the date of the election to receive credit. (b) The beginning date of the first subsequent period of service, for purposes of computation of contributions 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.