40 ILCS 5/15-136.1
Effective January 1, nearest the first anniversary of retirement, or January 1, nearest the annuitant's 65th birthday, whichever is later, the annuitant shall receive a supplemental annuity of 0.125% of the monthly retirement annuity which was provided under Rule 1, Rule 2, or Rule 3 of Section 15-136, multiplied by the number of full months which elapsed from the date of retirement through December 31, 1971, 0.1667% of such annuity multiplied by the number of full months which elapsed from January 1, 1972 through December 31, 1977, and 0.25% of such annuity multiplied by the number of full months which elapsed from January 1, 1978 to the effective date of the supplemental annuity.
On each January 1 thereafter during the annuitant's lifetime, he or she shall receive an additional supplemental annuity of 3% of the monthly annuity provided under Rule 1, Rule 2 or Rule 3 of Section 15-136. The change made in this Section by P.A. 81-970 is effective January 1, 1980 and applies to each annuitant whose status as an employee terminated before August 15, 1969.
The supplemental annuity is payable only if the annuitant files with the board, an agreement to pay to the system, an amount equal to 1% of his or her monthly final rate of earnings multiplied by the number of years of service credited on the date of retirement. The payment shall be made in a lump sum, and if it is received by the board more than 30 days after the effective date of the supplemental annuity, the supplemental annuity shall be deferred to the first day of the month following receipt of the payment.
Beginning January 1, 1990, all automatic annual increases payable under this Section shall be calculated as a percentage of the total annuity payable at the time of the increase, including all increases previously granted under this Article.
40 ILCS 5/15-136.1