Updated October 2026
Nearly every US state teacher retirement system — CalSTRS, Texas TRS, Illinois TRS, and dozens more — pays a defined-benefit pension built from the same three-part formula: Annual pension = Final Average Salary (FAS) × Years of Service × Multiplier. The exact numbers behind each part differ state by state (and often tier by tier within the same state), but the structure is identical everywhere. This page walks through what each part actually means and why small differences compound into large ones.
FAS is not your final year's salary — it's an average over a defined period, and that period varies enormously by state: some use your highest single year, others average your highest 3, 5, or even 8 years. A state that averages 8 years instead of 3 will generally produce a lower FAS for someone whose salary rose sharply near retirement, because more lower-paid years dilute the average. This is one of the biggest reasons two teachers with identical final salaries can retire with noticeably different pensions.
This is your total credited service time, which usually means full-time years actually worked but can also include purchased service credit (military time, time in another state's system) or partial credit for part-time years, depending on your plan's rules. Vesting requirements (often 5-10 years) must be met before any pension is payable at all, regardless of the formula.
The multiplier (also called the "benefit factor" or "accrual rate") is set by your state's retirement system and is often tiered — by your hire date, your age at retirement, or your total years of service. Because it's multiplied against your entire FAS × years figure, even a 0.2 percentage-point difference in multiplier is a 10% swing in your whole pension. That's exactly what the calculator's sensitivity table shows: hold FAS and years fixed, and watch how much the final number moves as the multiplier changes by just a few tenths of a point.
Take a teacher with a $75,000 FAS, 28 years of service, and a 2.2% multiplier (roughly in line with several large state systems): $75,000 × 28 × 0.022 = $46,200/year, or $3,850/month. Now change only the multiplier to 2.0%: $75,000 × 28 × 0.020 = $42,000/year — a $4,200/year difference from a 0.2-point change alone, with FAS and years held completely constant.
This formula is the right shape everywhere, but every state attaches its own rules to each variable: FAS averaging periods, age-graded or service-graded multiplier tables, hire-date tiers that can differ sharply for people hired before vs. after a reform year, and separate provisions for cost-of-living adjustments and Social Security interactions that aren't modeled in a simple formula at all. Use this calculator to understand the mechanics and sanity-check a number — then confirm your exact figure with your own state system's official member portal or benefit calculator before making any retirement decision.
This is an educational estimate, not financial or retirement advice. Multiplier and FAS rules shown anywhere on this site are illustrative and change over time — verify your exact figures with your state's official pension system.