Tier I — those who joined TRS before July 1, 1973.
Tier II — those who joined TRS after June 30, 1973 and before July 27, 1976
Tier III — those who joined TRS after July 26, 1976 and before September 1, 1983
All Tier III members may retire under Tier IV.
Tier IV (age 62) — those who joined TRS after August 31, 1983 but prior to Feb. 28, 2008. Many Tier IV members have opted into the 55/25 plan.
Tier IV (55/27) — those who joined after Feb. 28, 2008 but prior to April 1, 2012.
Tier VI — those who joined the retirement system after March 31, 2012.