For a participant who first becomes a participant of this System before August 10, 2009 (the effective date of Public Act 96-207):
For a participant who first becomes a participant of this System on or after August 10, 2009 (the effective date of Public Act 96-207) and before January 1, 2011 (the effective date of Public Act 96-889), the average monthly salary obtained by dividing the total salary of the participant during the period of: (1) the 48 consecutive months of service within the last 120 months of service in which the total compensation was the highest, or (2) the total period of service, if less than 48 months, by the number of months of service in that period.
For a participant who first becomes a participant of this System on or after January 1, 2011 (the effective date of Public Act 96-889), the average monthly salary obtained by dividing the total salary of the participant during the 96 consecutive months of service within the last 120 months of service in which the total compensation was the highest by the number of months of service in that period; however, beginning January 1, 2011, the highest salary for annuity purposes may not exceed $106,800, except that that amount shall annually thereafter be increased by the lesser of (i) 3% of that amount, including all previous adjustments, or (ii) the annual unadjusted percentage increase (but not less than zero) in the consumer price index-u for the 12 months ending with the September preceding each November 1. "Consumer price index-u" means the index published by the Bureau of Labor Statistics of the United States Department of Labor that measures the average change in prices of goods and services purchased by all urban consumers, United States city average, all items, 1982-84 = 100. The new amount resulting from each annual adjustment shall be determined by the Public Pension Division of the Department of Insurance and made available to the Board by November 1 of each year.
40 ILCS 5/2-108.1