Illinois TRS Calculator: How to Use It
Both Illinois TRS tiers use the same 2.2% multiplier. That is where the similarity ends. Tier 2 members face an 8-year FAS window, a salary cap, and a retirement age 7 years later than Tier 1. The calculator shows exactly how large that gap is for your specific numbers.
What this calculator does
The Illinois TRS Calculator applies the 2.2% formula to your tier-appropriate final average salary and projected service years. For Tier 2 it limits the average to $129,192.26, the 2026-27 earnings limit. It checks every eligibility path, including Tier 1's age 62 with 5 years, and projects the COLA with its real start date: no earlier than 61 for Tier 1 (3% compounded after a catch-up) and no earlier than 67 for Tier 2 (simple, 1.5% assumed).
What each input means
Membership tier
Joined TRS before January 1, 2011: Tier 1. Joined on or after January 1, 2011: Tier 2. Your tier appears on your TRS annual benefit statement. If you left and returned to teaching in Illinois, the gap length and whether you took a refund of contributions determines your tier on return. Contact TRS if you have any uncertainty.
Current age and years of creditable service
Creditable service is your total TRS-credited years, including part-time service that has been converted to full-time equivalents. Decimals are accepted. The calculator projects your service at your planned retirement age by adding the gap between your current age and your target date.
Final average salary
For Tier 1: the average of your highest 4 consecutive years within the last 10. For Tier 2: the highest 8 consecutive years within the last 10, with each year limited to that year's earnings limit ($129,192.26 for 2026-27). Enter your current annual salary as a starting point. If your salary has been rising, the actual FAS at retirement will be higher. If you are Tier 2 and earn above the cap, the calculator automatically applies it.
Planned retirement age
Tier 1 members can retire unreduced at 60 with 10+ years, 62 with 5+ years, or 55 with 35+ years. Tier 2 members need 67 with 10+ years.
Understanding the outputs
The 75% of FAS benefit cap appears once you have accumulated enough service. Tier 1 members hit it at approximately 34 years (34 x 2.2% = 74.8%). Tier 2 members hit the same threshold at the same service level, but their FAS is lower due to the longer averaging window and salary cap, so the capped dollar amount is also lower.
The COLA projections show a meaningful long-term difference between the tiers. A Tier 1 member retiring at 61 with $4,000 a month reaches about $6,232 after 15 increases at 3% compounded. A Tier 2 member retiring at 67 with $3,200 a month and 15 increases at 1.5% simple reaches $3,920. Retire earlier than 61 or 67 and the first increase waits.
Illinois TRS members generally do not participate in Social Security from their teaching employment. WEP and GPO rules previously applied if you had other Social Security credits, but both were repealed in January 2025.
The 8-year FAS window in practice
A Tier 2 teacher who spent years 1-8 earning $45,000-$60,000 but now earns $90,000 faces an 8-year average that pulls heavily from the lower-salary years. A 4-year average would capture mostly the higher years. The difference can reduce the calculated FAS by $10,000 to $20,000, translating into $2,200 to $4,400 less per year in pension income at a 22-year service level.
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Frequently asked questions
What is the difference between Illinois TRS Tier 1 and Tier 2?
Both use 2.2% per year. Tier 1 (joined before Jan 1, 2011): 4-year FAS window, earnings limited only by the federal cap ($360,000 for 2026-27, for members who joined after June 30, 1996), unreduced at 60/10, 62/5 or 55/35, 3% compounding COLA from age 61 at the earliest. Tier 2 (joined Jan 1, 2011+): 8-year FAS window, earnings limited to $129,192.26 for 2026-27, unreduced at 67/10, simple lesser-of-3%-or-half-CPI-U COLA from age 67 at the earliest.
How does the Illinois TRS benefit formula work?
2.2% x years of service x final average salary, capped at 75% of FAS. The cap is hit at approximately 34 years of service. Any additional service beyond that does not increase the benefit.
When can I retire without a penalty under Illinois TRS?
Tier 1: age 60 with 10+ years, age 62 with 5+ years, or age 55 with 35+ years. Early option: age 55 with 20+ years at 0.5%/month reduction before 60. Tier 2: age 67 with 10+ years. Early option: age 62 with 10+ years at 0.5%/month before 67.
How does the Illinois TRS COLA work differently for each tier?
Tier 1: the first increase comes January 1 after the later of your first retirement anniversary or age 61, catching up 3% for each full year retired; after that, 3% compounded. Tier 2: starting January 1 on or after the later of age 67 or your first anniversary, the lesser of 3% or half of CPI-U, figured on the original benefit (no compounding).
What is the Illinois TRS salary cap for Tier 2 members?
TRS applies it by school year: $127,283.01 for July 2025-June 2026 and $129,192.26 for July 2026-June 2027. It rises each year by 3% or half of CPI-U, whichever is less. Earnings above it don't count toward final average salary. Confirm the current figure with TRS.