40 ILCS 5/9-118

"Effective rate of interest", "interest at the effective rate", or "interest": Interest at 4% per annum for a present employee, or for a future entrant or re-entrant who was a participant or contributor on January 1, 1954; and at 3% per annum for a future entrant or re-entrant who becomes a contributor after January 1, 1954. In all cases involving reserves, credits, transfers, and charges, "effective rate of interest", "interest at the effective rate" or "interest" shall be applied at these rates.