California Code, Government Code - GOV § 31615

Regular interest at the actuarial rate, or at the highest rate possible if net earnings, as defined in Section 31613 are not sufficient to credit the full actuarial rate, shall be credited semiannually on June 30 and December 31 to all contributions, reserves, and accounts in the retirement fund, except the Contingency Reserve Account, which have been on deposit for six months immediately prior to those dates.

Interest at the actuarial rate, compounded semiannually, shall be used in the calculation of benefits under any mortality table adopted by the board of supervisors. No interest shall be credited to a member's account after the termination of the member's county service, unless the member has elected, in writing, to leave his or her accumulated contributions in the retirement fund and be granted a deferred retirement allowance, or the surviving spouse of a deceased member or the legally appointed guardian of the member's unmarried children under age 18 has elected to leave a death benefit on deposit as provided for in Section 31781.2.