At the end of each fiscal year the board may credit to all contributions held in the fund at June 30th of the then current fiscal year, such interest in excess of the current rate as it deems proper in the light of the earnings on the fund during that fiscal year, but not more than the difference between such earnings and the interest credited at the current rate to contributions during that year.
Source:
Section 9353.4, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=9353.4..