Any additional earnings credit declared shall be determined as a specified percentage increase in the closing balance of each employee account and employer account with respect to the Cash Balance Benefit Program measured as of the last day of the plan year. The additional earnings credit shall be credited to employee account and employer account balances as of the date the board declares the additional earnings credit is to be applied. The additional earnings credit shall not be credited to employee accounts and employer accounts that have been transferred to the Annuitant Reserve for payment of an annuity under the Cash Balance Benefit Program.