The board shall allow to each fund of the retirement system regular interest on the average amount credited for the preceding year to each fund, with the exception of the expense fund, from the interest and dividends earned from investments. The regular interest shall be at such rate, compounded annually, as shall be determined by the board on the basis of the interest earnings of the retirement system for the preceding year and of the probable earnings to be made in the judgment of the board, during the immediate future. Until changed by the board the regular rate of interest shall be three per cent (3%) per annum.
T.C.A. § 8-3443