If you're a federal employee under FERS, your retirement rests on what's often called a three-legged stool: your FERS pension, your Thrift Savings Plan (TSP), and Social Security. The calculator above estimates the first leg. Here's how that number is built, how your retirement age changes it, and where the other two legs come in.
How the FERS pension is calculated
Your FERS basic annuity comes from a straightforward formula with three ingredients:
- Your high-3 — the average of your three highest consecutive years of basic pay (usually, but not always, your final three years).
- Your years of creditable service — how long you've worked under FERS, including unused sick leave in many cases.
- Your multiplier — 1.0% in most cases, or 1.1% if you retire at age 62 or later with at least 20 years of service.
Put together, the formula is: high-3 × years of service × multiplier. That's the same math the quick estimate above runs, and it's the foundation of every FERS retirement projection.
Federal Employee Note
The 1.1% multiplier is one of the most overlooked levers in federal retirement. Staying until age 62 with 20+ years isn't just one more year of salary in your high-3 — it permanently raises your pension by about 10% for the rest of your life.
Retirement age examples
The clearest way to see how timing matters is to run the same person at different ages. Assume a high-3 of $90,000:
Retiring at your MRA (age 57) with 30 years
$90,000 × 30 × 1.0% = $27,000/year (about $2,250/month)
Plus the FERS Special Retirement Supplement until age 62 — more on that below.
Retiring at age 62 with 30 years
$90,000 × 30 × 1.1% = $29,700/year (about $2,475/month)
The 1.1% multiplier adds roughly $2,700 a year for life, and Social Security is now available.
Retiring at age 60 with 20 years
$90,000 × 20 × 1.0% = $18,000/year (about $1,500/month)
Eligible for an immediate, unreduced annuity, plus the supplement until 62.
When can you actually retire under FERS?
You qualify for an immediate, unreduced annuity at your Minimum Retirement Age (MRA) with 30 years, at age 60 with 20 years, or at age 62 with 5 years. You can also leave at your MRA with at least 10 years (the "MRA+10" option), but that annuity is reduced for each year you're under 62. Your MRA falls between 55 and 57 depending on the year you were born — 57 for anyone born in 1970 or later.
The FERS Special Retirement Supplement
If you retire before 62 with an immediate, unreduced annuity, FERS pays you an extra monthly amount called the Special Retirement Supplement. It's designed to approximate the Social Security benefit you earned during your federal career, and it bridges the income gap until you reach 62 and can claim Social Security itself.
A rough way to picture it: take the Social Security benefit you'd be entitled to at 62, then multiply by your years of FERS service divided by 40. Someone with 30 years of service would receive roughly 30/40 — about three-quarters — of that estimated benefit each month until 62.
Watch Out
The supplement is subject to a Social Security earnings test. If you take another job after retiring and earn above the annual limit, your supplement can be reduced or paused. It also ends the month you turn 62, whether or not you actually claim Social Security then.
How your TSP fits in
Your pension is guaranteed income, but it's rarely enough on its own — and that's by design. The TSP is the second leg of the stool, and for most federal employees it ends up being the largest single source of retirement income. The government matches your contributions up to 5%, your balance grows tax-deferred (or tax-free in the Roth TSP), and how you draw it down in retirement is entirely up to you.
Because the TSP depends on your balance, your contribution rate, your investment mix, and how many years it keeps compounding, it's the piece a one-line formula can't capture. That's exactly where the full calculator earns its keep — it projects your TSP forward to your retirement date and translates the balance into realistic monthly income alongside your pension and Social Security.
Pro Tip
Always contribute at least 5% of your salary to your TSP. Anything less leaves free matching money on the table — it's an immediate, guaranteed return you won't find anywhere else.
Putting all three legs together
The pension estimate above answers one question: what will my FERS annuity be? But the question that actually keeps federal employees up at night is the bigger one — will my total income be enough to retire when I want to? Answering that means stacking the pension, the supplement, your TSP withdrawals, and Social Security into a single monthly number, and then testing what happens if you retire two years earlier, or later.
That's what the complete Stone Rose Federal Retirement Calculator is built to do. It takes the pension math you've seen here and adds every other moving part, so you walk away with a projected monthly retirement income instead of a single piece of the puzzle.
Frequently asked questions
How is the FERS pension calculated?
High-3 average salary × years of creditable service × 1.0% (or 1.1% if you retire at 62+ with at least 20 years). A $90,000 high-3 with 30 years yields $27,000/year at 1.0% or $29,700/year at 1.1%.
What's the difference between retiring at my MRA and at 62?
Retiring at 62+ with 20+ years raises your multiplier from 1.0% to 1.1% — about a 10% larger pension for life. Retiring earlier can still work because the FERS supplement bridges your income to 62, but the multiplier bump is only available at 62.
What is the FERS Special Retirement Supplement?
An extra monthly payment that approximates the Social Security you earned in federal service, paid from retirement until age 62. It's generally available with an immediate, unreduced annuity and is subject to a Social Security earnings test.
Does this calculator include my TSP and Social Security?
The quick estimate here is pension-only. The full Federal Retirement Calculator models your TSP growth and withdrawals, Social Security timing, the supplement, and additional accounts to project your total monthly income.
When can I retire under FERS?
Immediate, unreduced annuity at your MRA with 30 years, age 60 with 20 years, or age 62 with 5 years. MRA+10 is also possible but reduced. Your MRA is 55–57 depending on your birth year.