(a) Effective as of December 31 of each year, the board of trustees shall make the following allocations from the interest fund that in the aggregate equal the net investment income or loss for the year:
(1) to the supplemental disability benefits fund, interest on the mean amount in the supplemental disability benefits fund during that year;
(2) to the supplemental death benefits fund, interest on the mean amount in the supplemental death benefits fund during that year;
(3) to the accounts in the benefit accumulation fund, an amount derived by applying a positive or negative rate, as determined by the board of trustees in its sole discretion to the January 1 balances of that year for each of those accounts; and
(4) to the interest reserve account of the endowment fund, a positive or negative amount as determined by the board of trustees in its sole discretion.

(b) In making allocations under this section, the board of trustees shall, without regard to the amount of net investment income or loss for the calendar year, first allocate interest as specified in § 855.316(a) to those funds or accounts referenced in Subsections (a)(1) and (2) of this section. The board shall then allocate the remaining net investment income or loss between the funds or accounts referenced in Subsections (a)(3) and (4) of this section in rates or amounts determined by the board in its sole discretion. The board of trustees shall accumulate the amount of assets in the interest reserve account of the endowment fund that the board in its sole discretion determines is necessary:
(1) to provide adequate reserves to:
(A) mitigate the effects of future investment return volatility and insufficient net investment income; and
(B) provide reasonable rate stabilization for participating municipalities;
(2) to provide adequate reserves against special and contingency requirements of other funds of the system; and
(3) to provide the amount required for the administration expenses of the system for the following year.
(c) After the requirements of the interest reserve account of the endowment fund have been satisfied, the board of trustees may transfer any of the amount remaining in the interest fund to the general reserves account of the endowment fund to maintain adequate reserves against special requirements of other funds of the retirement system.
(d) After the requirements of the interest reserve account and the general reserves account of the endowment fund have been satisfied, the board of trustees shall transfer any amount remaining in the interest fund to the distributive benefits account of the endowment fund.