40 ILCS 5/5-207
All gains from investment and all interest earnings shall be credited, and all losses from investments shall be charged to this reserve. From this reserve shall be transferred all amounts due in interest upon balances existing in the city contribution, the salary deduction, the prior service annuity, and the gift reserves.
Such amounts as shall be necessary, according to the American Experience Table of Mortality and interest at 4% per year or the Combined Annuity Mortality Table with 3% per annum as to the assets or liabilities to which either Table may be applicable in accordance with the provisions of this Article, to establish a balance in the annuity payment reserve equal to the liabilities chargeable thereto (including among such liabilities and in addition to all other liabilities of such reserve the present values of all annuities entered upon or fixed, and not entered upon to be charged to such reserve) shall be transferred to the annuity payment reserve at least once each year.
That portion of the annual investment earnings on the fund's invested assets exclusive of gains or losses on sales or exchanges of assets during the year on the fund's invested assets as required by Section 5-167.2 of this Article shall be transferred from the investment and interest reserve to the Supplementary Payment Reserve set forth in Section 5-167.2.
Any balance in the investment and interest reserve shall be either charged or credited to the Prior Service Annuity Reserve depending on whether a deficiency or surplus exists in investment and interest reserve.
40 ILCS 5/5-207