Conn. Gen. Stat. § 5-156e

Any lump sum payment to a retired member of the state employees retirement system which represents the difference between the preaudit benefit received by the member and the actual benefit to which the member is entitled shall include interest at the rate of five per cent per year from six months following the date of retirement to the date of such lump sum payment. The payment of such interest shall be made from the State Employees Retirement Fund.