Coast FIRE with a Pension: How Guaranteed Income Shrinks Your Number

A pension is the closest thing to a cheat code in retirement planning — and if you’ll have one, running a Coast FIRE calculator with pension income included can cut your required portfolio dramatically. A pension is a guaranteed income floor: money that shows up every month whether the market cooperates or not. Every dollar of it is a dollar your investments don’t have to produce.

But pensions come with wrinkles that Social Security doesn’t: lump-sum buyout offers, COLA vs fixed payments, and start dates that rarely match your retirement date. This guide walks through each one, then runs a complete worked example. (For the basics of the formula itself, start with What is Coast FIRE?.)

The Core Adjustment: Subtract Guaranteed Income First

The standard Coast FIRE math has two steps:

1. FIRE number = annual retirement spending × 25 (the 4% rule)
2. Coast FIRE number = FIRE number ÷ (1 + real return)^years until retirement

A pension plugs into step 1, exactly like any other guaranteed income stream:

• Portfolio-funded spending = annual spending − annual pension
• Adjusted FIRE number = portfolio-funded spending × 25

Spend $48,000 a year and expect a $1,800/month ($21,600/year) pension? Your portfolio only needs to fund $26,400 a year. Your FIRE number drops from $1,200,000 to $660,000 — a 45% reduction. Then that smaller number gets discounted back to today as usual.

Simple enough. The complications are in the details.

COLA vs Fixed Pensions: The Inflation Trap

The single most important question about your pension: does it have a cost-of-living adjustment?

• COLA pension (common for federal employees and many public plans): payments rise with inflation, so the benefit keeps its purchasing power. You can subtract it from spending directly, since both are effectively in today’s dollars.
• Fixed pension (most private-sector plans): the dollar amount never changes. Inflation quietly eats it alive.

Here’s how much that matters. At 3% inflation, a fixed $2,000/month pension is worth, in today’s dollars:

• After 10 years: $2,000 ÷ 1.03^10 ≈ $1,488/month
• After 20 years: $2,000 ÷ 1.03^20 ≈ $1,107/month
• After 30 years: $2,000 ÷ 1.03^30 ≈ $824/month

A “generous” fixed pension loses almost half its real value over a 20-year retirement. If your pension has no COLA, you must discount it to today’s dollars before subtracting it from your spending target — otherwise you’ll undershoot your Coast FIRE number. The worked example below shows both versions side by side.

Lump Sum vs Monthly Annuity

Many private plans offer a choice: take the monthly annuity for life, or take a one-time lump sum and invest it yourself. There’s no universal right answer, but there’s a useful first-pass test:

Implied payout rate = annual annuity ÷ lump sum offered

• Lump sum offer: $300,000
• Annuity: $21,600/year ($1,800/month)
• Implied payout rate: $21,600 ÷ $300,000 = 7.2%

Compare that to the 4% safe withdrawal rate. A 7.2% payout rate means the plan is offering you far more guaranteed income than the same money would safely generate in the market — which generally favors the annuity, especially if it has a COLA and you’re in good health.

Lean toward the lump sum when the payout rate is low (below ~5%), the pension is fixed with no COLA, you have real doubts about the plan’s solvency, or leaving money to heirs matters to you. Lean toward the annuity when the payout rate is high, there’s a COLA, and longevity runs in your family. And remember: if you take the lump sum, that money simply becomes part of your invested assets in the Coast FIRE calculator — the math doesn’t change, only who manages it.

Bridge Years: When the Pension Starts After You Retire

Pensions typically start at a plan-defined age — often 60 or 65 — not whenever you decide to stop working. Retire at 58 with a pension that starts at 65, and your portfolio carries 100% of your spending for seven years.

Handle it the same way you’d handle any income stream with a delayed start: split your need into a bridge fund (full spending until the pension begins) and a long-term fund (spending minus pension afterward), and discount each piece back to today separately.

Worked Example: Age 40, Retire at 65, $48K Spending

Meet Sam: age 40, plans to retire at 65 with $48,000/year of spending in today’s dollars, and is on track for a $1,800/month pension starting at 65. Assumptions match our calculator: 7% nominal return, 3% inflation, 4% withdrawal rate — a real return of 3.88% (1.07 ÷ 1.03 − 1), and 25 years of compounding between now and retirement.

Scenario A: No pension (baseline)

• FIRE number at 65: $48,000 × 25 = $1,200,000
• Coast FIRE number at 40: $1,200,000 ÷ 1.0388^25 = $1,200,000 ÷ 2.5922 ≈ $462,900

Scenario B: Pension WITH a COLA

The pension keeps pace with inflation, so subtract it directly:

• Portfolio-funded spending: $48,000 − $21,600 = $26,400/year
• FIRE number at 65: $26,400 × 25 = $660,000
• Coast FIRE number at 40: $660,000 ÷ 2.5922 ≈ $254,600

Scenario C: Pension WITHOUT a COLA (fixed)

First, discount the fixed pension to today’s purchasing power. Sam retires in 25 years, and at 3% inflation:

• Real value at 65: $1,800 ÷ 1.03^25 = $1,800 ÷ 2.0938 ≈ $860/month (~$10,300/year in today’s dollars)
• Portfolio-funded spending: $48,000 − $10,300 = $37,700/year
• FIRE number at 65: $37,700 × 25 = $942,100 (approximately)
• Coast FIRE number at 40: $942,100 ÷ 2.5922 ≈ $363,400

Side by Side

Same pension on paper — a $108,800 difference in today’s required balance depending on three letters: COLA. Check your plan documents before you run your numbers. And because Sam’s pension starts at the same age he retires, no bridge fund is needed here; if he retired at 60 instead, he’d add five years of full spending ($240,000, discounted back) on top.

How to Find Out What Your Pension Will Actually Pay

Don’t guess at the benefit amount — get it in writing:

• Request a benefit estimate from your plan administrator. Most plans provide an annual statement or an online estimator showing your projected monthly benefit at different retirement ages.
• Understand the vesting schedule. You’re only entitled to the benefit once vested (often 5 years of service). Leave before vesting and you may get nothing beyond your own contributions.
• Check the early-retirement reduction. Many plans cut the benefit by 3–6% for each year you claim before the plan’s normal retirement age — the mirror image of Social Security’s delayed credits.
• Ask about survivor options. A joint-and-survivor annuity pays less per month (typically 5–15% less) but keeps income flowing to your spouse. For couples, that trade-off deserves real thought; our Coast FIRE for couples guide covers the coordination side.

Stacking a Pension with Social Security

If you’ll have both, you have two income floors — and the math compounds in your favor. Subtract both from your spending target (adjusting each for COLA and start date), then size bridge funds for any gaps before each one begins. A retiree spending $48,000 with a $21,600 COLA pension and $18,000 of Social Security only needs their portfolio to fund $8,400 a year long-term — a FIRE number of $210,000 instead of $1,200,000. One historical footnote: the Windfall Elimination Provision and Government Pension Offset once reduced Social Security for some pensioners whose work didn’t pay into the system, but the Social Security Fairness Act repealed both for benefits from 2024 onward — a meaningful boost for many public-sector retirees.

A Quick Word on Solvency

Private-sector pensions are insured by the Pension Benefit Guaranty Corporation (PBGC) up to legal limits, which fully cover most retirees. Public pensions depend on the financial health of the sponsoring state or city, and funding levels vary widely. Practical takeaways:

• Request your plan’s annual funding notice and know its funded percentage
• Don’t build a plan where the pension is your only income source
• If you’re decades from retirement, consider running your Coast FIRE math with the pension at 75–100% of its promised value as a stress test

The Bottom Line

A pension can nearly halve your Coast FIRE number — but only if you account for it honestly:

1. Confirm whether your pension has a COLA; discount fixed pensions for inflation first
2. Subtract the (inflation-adjusted) annual benefit from your spending before multiplying by 25
3. Add a bridge fund if the pension starts after your retirement date
4. Stress-test at 75% of the promised benefit

Start with your baseline: plug your numbers into the Coast FIRE calculator, see your current trajectory, and then layer your pension on top using the steps above. Curious how much time you have? Check your Coast FIRE number at 40 — or whatever age you are today.