In 1983, the Maine Legislature and Administration choose not to participate in the federal Social Security System for Public Service Employees (Legislators, Judges, Troopers, State Employees, Educators and some Municipal Employees) and choose to participate in the Maine Public Service Retirement System (MainePERS).  This decision impacts the method the federal Social Security System uses to determine the Social Security retirement benefits for MainePERS retirees.
Federal Social Security benefits are calculated based on the average monthly earnings over thirty-five years (AIME).  Once the AIME is determined, a three tiered formula is used to calculate the monthly Social Security retirement benefit.  The first $826 of the AIME provides 90% of the AIME as part of the Social Security benefit; the AIME amount between $827 and $4,980 provides 32% of the AIME as part of the Social Security benefit; and the AIME over $4,980 provides 15% of the Social Security benefit.
SOCIAL SECURITY CALCULATION WITHOUT THE WINDFALL PROVISION
The WINDFALL ELIMINATION PROVISION (WEP) changes the formula for determining the Social Security benefit with the intent to take into account the years someone was not paying Social Security because of another public pension versus no Social Security due to no employment.  For MainePERS retirees, the formula changes the percentage in the first tier of the formula from 90% to 40%.  The remaining two tiers are unchanged.
SOCIAL SECURITY CALCULATION WITH WINDFALL ELIMINATION PROVISION
https://www.ssa.gov/pubs/EN-05-10045.pdf
https://www.ssa.gov/benefits/retirement/planner/wep.html