FERS Pension: How the Federal Formula Actually Works

Federal retirement runs on one small formula, a retirement-age table most employees never read, and a TSP match that is easy to leave on the table. Here is all three, with the arithmetic shown.

By RetirePlot Editorial · Updated 2026-10-24 · 9 min read

FERS — the Federal Employees Retirement System — is a three-legged stool: a defined-benefit annuity, Social Security, and the Thrift Savings Plan. Each leg is modest alone; the system works because they stack. This guide shows the annuity formula, the retirement-age table that controls it, and what the TSP match adds on top.

The three legs of FERS

The legs are deliberately uncorrelated in the ways that matter: the annuity is inflation-exposed but market-proof, the TSP is market-driven but flexible, and Social Security sits in between. A plan that leans on only one leg inherits that leg's specific risk — which is why OPM's own retirement briefings treat the three as a system, not a menu.

The annuity formula, with numbers

The core computation fits on an index card:

Everything in that line is knowable years in advance: the high-3 rises on a predictable salary schedule, service years tick annually, and only the retirement date — which picks the multiplier — is yours to choose.

The high-3 is the average of your highest three consecutive years of basic pay (typically your last three). The multiplier is 1% per year of service — rising to 1.1% if you retire at age 62 or later with at least 20 years. Worked example, computed by the same engine the site's calculators use — high-3 of $98,000, 22 years of service:

Working two more years is worth $2,156 a year for the rest of your life in this example — the 1.1% tier plus two more years of service both pay. That gap is the single most underappreciated number in federal retirement planning. One more variable hides in the election paperwork: choosing a survivor annuity for a spouse reduces the monthly benefit while both are alive, in exchange for the survivor keeping an income afterward — and declining it requires your spouse's notarized consent. The calculator above shows the gross annuity; your election determines how much of it you actually keep.

When you are allowed to retire

Eligibility is a matrix of age and service. The three routes most employees weigh:

The MRA+10 reduction is where careers quietly get expensive: leaving at 57 with 20 years means five years of 5% compounding-off-the-top. Postponing the annuity start date to 62 avoids the reduction, at the cost of no income (and no FEHB continuation option) in between — an OPM tradeoff worth modeling before you sign anything. Service history can also add years: certain prior military and federal service is creditable after making a deposit, priced under OPM rules. For veterans, redeeming military time is often the highest-return "purchase" in the whole system — each added year raises the annuity at the full multiplier.

Two less-common routes complete the matrix, both with strings attached:

• Postponed retirement (MRA+10): leave now, start the annuity at 62 — the reduction disappears, but you get nothing (and usually no FEHB continuation) until then.
• Deferred retirement: resign before your MRA with at least 5 years — the annuity waits until 62 or 60/20, with no supplement and typically no retiree health benefits.

The FERS supplement

Retire under MRA+30 (or at 60 with 20 years) and OPM pays a special retirement supplement from your retirement date until age 62 — an estimate of the Social Security you earned from federal service, so you are not bridging three years on savings alone. It ends at 62 no matter when you claim Social Security, and it is subject to an earnings test if you work in between. One more wrinkle for early retirees: FERS cost-of-living adjustments on the annuity begin at age 62, so an MRA+30 retiree's pension can be fixed in nominal dollars for up to seven years — inflation is a real planning input for early federal retirees, not an abstraction.

Application mechanics matter here too: the supplement is computed and paid by OPM as part of the annuity package, not claimed separately from the SSA. Retirement paperwork runs through your agency's HR into OPM's online portal, and the pre-separation estimate is worth reconciling line by line against the first annuity statement.

The TSP leg and the 5% match

The Thrift Savings Plan works like a 401(k) with unusually low fees: agencies put in 1% automatically and match dollar-for-dollar up to another 4% — so contributing 5% of salary captures the full 5% agency contribution. Federal limits are the same ones in the 2026 limits guide, including catch-ups. One projection to size the leg — 5% deferral on a $98,000 salary with the full match, 7% returns, 0.04% fees, over the same 22 years:

The agency contributes about $133,765 of the projected $615,464 — money that exists only if you contribute your 5%. Below 5%, every skipped point of deferral is a point of match declined. Fees deserve one line too: the TSP's expense ratios sit among the lowest in the industry, and over a 22-year career the gap against a typical retail plan compounds into a visibly larger balance — a quiet annuity of its own. Note also that the Roth TSP option exists and follows the same federal limits; agency matching contributions, however, are always deposited on the traditional (pre-tax) side, so even a Roth-only contributor ends up holding a mixed balance.

Withdrawal flexibility has improved in recent years — partial withdrawals and installment payments are now available without forcing a full liquidation — but the TSP's real strength at retirement remains its fee level and its simplicity, not its feature count.

Putting the three legs together

Stack the example: the annuity at 62 pays $23,716 a year, Social Security (claimable from 62 with a reduction, or later at a bonus) covers a further slice, and the TSP fills whatever is left — tested against spending exactly the way the how-much-do-I-need guide describes. Federal employees often discover their annuity covers less of the total than assumed; that is not a flaw in FERS, it is the design. Before running your own numbers, gather four inputs:

• Your service computation date (SCD) — the start of creditable service, from your SF-50 or eOPF record.
• A high-3 estimate — the average of your highest three consecutive years of basic pay, usually your last three.
• Your age at the intended retirement date — it selects the eligibility route and the multiplier tier.
• A Social Security estimate — from your SSA statement, for the leg only the SSA can price.
• Your survivor-annuity election — the default protects a spouse at a cost to the monthly amount, and changing it requires spousal consent.

With those four, the formula on this page produces your gross annuity in one multiplication — and the calculators below the fold turn it into a monthly picture alongside the other two legs.

Sources and verification

1. OPM — FERS information (eligibility, annuity computation, supplement): opm.gov/retirement-services
2. OPM — FERS eligibility categories: opm.gov/retirement-services/fers-information
3. Thrift Savings Plan — contribution and match rules: tsp.gov
4. Social Security Administration — benefit estimates: ssa.gov
5. IRS Publication 721 — Tax Guide to U.S. Civil Service Retirement Benefits (taxation of the annuity): irs.gov/publications/p721

Want the formula against your own SCD and high-3? The FERS pension calculator computes the annuity and the 1.0%-vs-1.1% crossover directly.