Tenn. Code § 49-1529
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 this chapter 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 throughout his entire period of active service which would be sufficient to provide for the payment of any state annuity on his account. The rate per centum 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 per centum of the earnable compensation of all members obtained by deducting from the total liabilities of the accumulation account the amount of the funds in hand to the credit of that account and dividing the remainder by one per cent (1%) of the present value of the prospective future earnable compensation of all members as computed on the basis of the 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.
T.C.A. § 49-1529