Updated October 30, 2026. Quick answer: In the State Employees’ Retirement System of Illinois, a regular formula Tier 2 member (joined after December 31, 2010) needs a minimum of 10 years of credited service and can retire at age 67, or between ages 62 and 67 with a pension reduced one half of one percent for each month under 67. Tier 1 regular formula members (joined before January 1, 2011) can retire at age 60 with 8 years, or at any age under the Rule of 85.
Tier 2
“This information applies to individuals who became a member of SERS or a reciprocal system after December 31, 2010.” “To receive a pension benefit, you must have a minimum of 10 years of credited service with SERS. You may retire at: Age 67, with 10 years of service credit .” “A regular formula member can retire between the ages of 62-67 with 10 years of service with a pension reduced 1/2 of 1% for each month under age 67.”
Tier 1
“This information applies to individuals who became a member of SERS or a reciprocal system before January 1, 2011.” “You may retire at: Age 60, with 8 years of service credit .” The Rule of 85: “Any age, when your age (years & whole months) plus years of service credit (years & whole months) equal 85 years (1020 months) ( Rule of 85 ).” “A regular formula member can retire between the ages of 55-59 with 25-29 years of service with a pension reduced 1/2 of 1% for each month under age 60.”
What the pension is based on
“Coordinated: 1.67% for each year of service Non-Coordinated: 2.2% for each year of service”. Tier 1 pay: “Final average compensation is the 48 highest consecutive months of service within the last 120 months of service.” Tier 2 pay: “For regular formula employees, final average compensation is the average of the 96 highest consecutive months of service within the last 120 months of service.”
A worked example with invented numbers
Take an invented coordinated Tier 2 member with 25 years of service who retires at 67. That is 25 years at 1.67%, or 41.75% (computed) of a final average salary of $70,000 (invented, for the computation), which comes to $29,225 a year (computed).
Now take the same member retiring at 62, 60 months before 67. That is 25 years at 1.67%, or 41.75% (computed) of a final average salary of $70,000 (invented, for the computation), which comes to $29,225 a year (computed). The reduction is 60 months under age 67 at 1/2 of 1% each, which is 30% (computed). The pension after the reduction is $20,458 a year (computed).
What the documents do not say
The Tier 1 page prints a minimum of 8 years only on the age 60 line, so this page does not claim 8 years for the Rule of 85. Tier 2 pages print no rule of N and no age-plus-service route, and no source read uses the label Tier 3. The alternative formulas are not summarized, and the statute text was not read. Neither page prints a revision date. Other member groups are not covered.
Common mistakes
- Using the Tier 1 ages for someone who joined after December 31, 2010.
- Reading 85 as an age. It is age plus service credit, in years and whole months.
- Forgetting that the formula depends on Social Security coordination: the factor differs for coordinated and non-coordinated members.
Related: Illinois SERS retirement decisions, the Illinois SERS COLA for 2027, how public pension decisions work, and whether Illinois taxes pensions.
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Answer againSources
- State Retirement Systems of Illinois (SERS), Tier 2 Regular Formula: ilsrs.illinois.gov
- State Retirement Systems of Illinois (SERS), Tier 1 Regular Formula: ilsrs.illinois.gov
- Related official page (not quoted): IRS Tax Topic 410, Pensions and annuities: www.irs.gov
- Related official page (not quoted): IRS Tax Topic 411, Pensions: the General Rule and the Simplified Method: www.irs.gov
Read from the primary documents linked above on October 30, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer or the IRS itself is the right place to confirm anything consequential.