FERS vs CSRS: Which Federal Retirement System Are You Under (and Why It Changes Everything)
If you were first hired by the federal government on or after January 1, 1984, you're almost certainly under FERS (Federal Employees Retirement System). Hired before that and never left? You may be one of the shrinking group still under CSRS (Civil Service Retirement System). The two systems calculate retirement income so differently that using the wrong assumptions can throw a retirement estimate off by six figures over a lifetime.
The one-sentence difference
CSRS is a single big pension. FERS is a smaller pension plus Social Security plus the TSP with matching — three streams instead of one.
Pension formulas, side by side
CSRS uses a tiered formula on your high-3 average salary: 1.5% for the first 5 years, 1.75% for years 5–10, and 2% for everything beyond 10, capped at 80% of high-3 (about 41 years, 11 months of service). A 30-year CSRS career replaces roughly 56.25% of high-3 — before any unused sick leave credit.
FERS uses a flat 1% of high-3 per year of service — bumped to 1.1% if you retire at 62 or later with at least 20 years. That 62/20 bump is the single most consequential timing decision in FERS: 30 years × 1.1% = 33% of high-3 instead of 30%. On a $100,000 high-3 that's $3,000 more per year, every year, with COLAs compounding on top.
Social Security
CSRS employees generally didn't pay into Social Security for their federal service. Eligible FERS employees can receive the FERS Special Retirement Supplement after an immediate unreduced retirement before 62. It estimates the Social Security earned during FERS service and ends around age 62 under OPM's month-of-entitlement rules.
TSP matching
Under FERS the government automatically contributes 1% of salary and matches up to another 4% (full match at a 5% employee contribution). CSRS employees can use the TSP but get no match. Over a 30-year career, the FERS match alone — invested — routinely grows into several hundred thousand dollars. Any FERS estimate that looks only at the pension misses a third of the picture.
COLAs: the quiet difference
CSRS annuities get the full CPI adjustment every year. FERS gets the "diet COLA": full CPI when inflation is 2% or less, 2% flat when inflation is 2–3%, and CPI minus 1% when it's above 3% — and in most cases FERS COLAs don't begin until age 62. Over a 25-year retirement in inflationary decades, this gap compounds into real money, and most self-made spreadsheets ignore it entirely.
Survivor benefits
CSRS: a full survivor annuity is 55% of the base annuity, costing just under 10% of the annuity. FERS: 50% (cost: 10% reduction) or 25% (cost: 5%). Electing less than a full survivor benefit for a spouse requires notarized spousal consent in both systems.
Which is "better"?
Neither, universally. CSRS front-loads certainty (bigger pension, full COLA); FERS spreads risk and reward across three streams and rewards long TSP discipline and smart claiming ages. What matters is that your projection uses your system's actual rules — the right accrual rate, the right COLA behavior, the right Social Security interaction.
FAQ
I have both CSRS and FERS service. What am I?
Likely a "CSRS Offset" or a FERS transferee with a CSRS component. Your annuity is computed in two pieces under two formulas — this is exactly the situation where generic calculators fail.
Does unused sick leave count in both systems?
Yes — it's added to service time for the annuity computation (not for eligibility) in both, using OPM's 2,087-hour conversion.
Where do I check which system I'm in?
Block 30 of your SF-50 (retirement plan code): codes K, KR, L, M, N are FERS variants; 1 and 6 are CSRS; C/E are CSRS Offset.
Want the number, not the theory? The FERS Report calculator runs your high-3, service years, sick leave, survivor election, and the 62/20 multiplier in about two minutes. The $29 report provides the written pension computation and verification checklist.
Educational content only — not financial, tax, or legal advice. Verify your figures with OPM and your HR retirement specialist before making retirement decisions.