Mo. Rev. Stat. § 86.157
On the basis of regular interest and of such mortality and other tables as shall be adopted by the board of trustees, the actuary engaged by the board to make each valuation required by sections 86.010 to 86.193 during the period over which the accrued liability contribution is payable, immediately after making such valuation, shall determine the uniform and constant percentage of the earnable compensation of the average new entrant, which, if contributed throughout his entire period of active service, would be sufficient to provide for the payment of any death benefit or pension payable on his account. The rate percent so determined shall be known as "the normal contribution rate". After the accrued liability contribution has ceased to be payable the normal contribution rate shall be the rate percent of the earnable compensation of all members obtained by deducting from the total liabilities of the fund the amount of the funds in hand to the credit of the fund and dividing the remainder by one percent of the present value of the prospective future compensation of all members as computed on the basis of mortality and service tables adopted by the board of trustees and regular interest. The normal rate of contribution shall be determined by the actuary after each valuation.
§ 86.157, RSMo