What is a Coast FIRE number?

It is the portfolio size that, left untouched, compounds into your full FIRE number by your chosen retirement age. The formula is FIRE number ÷ (1 + return)^years. Once you hold that amount, you only need to earn enough to cover current living costs — retirement funds itself.

Does reaching Coast FIRE mean I can quit my job?

No. Coast FIRE means you can stop saving for retirement, not stop earning. You still need income to pay today's bills until retirement age — the difference is that every dollar you earn can be spent, because the portfolio finishes the job on its own.

Why does the Coast FIRE number change so much with age?

Because compounding is exponential in time. At a 7% real return, money doubles roughly every 10 years, so a 30-year-old targeting 65 needs about a tenth of the final goal, while a 50-year-old needs about a third. The earlier you front-load savings, the smaller the required amount.

Coast FIRE Calculator — When Can You Stop Saving?

FIRE Awareness · free calculator · runs in your browser

Current age

Retirement age

Current invested net worth ($)

Monthly savings ($)

Monthly expenses in retirement ($)

Expected return (%/yr, after inflation)

Safe withdrawal rate (%)

Full FIRE number at retirement

—

Coast FIRE number — what you need invested today

—

so growth alone reaches the goal by retirement age

This is the rough math. FIRE Awareness tracks the real thing — your live safe-to-spend number, worked back from your actual FIRE date.

Try the live demo — no signup

What Coast FIRE means

Coast FIRE is the point where your retirement is already funded — you just can't spend it yet. Once your invested portfolio is big enough, compounding alone will grow it into your full FIRE number by retirement age, with zero further contributions. From that day on, you only need to earn enough to cover your current bills. No more saving for retirement, ever. That's why people call it "coasting."

It's a fundamentally different milestone from full FIRE. Full FIRE asks: when can I stop working? Coast FIRE asks the gentler question: when can I stop saving? — and the answer usually arrives a decade or more earlier.

The formula, plainly

First compute the full FIRE number, then discount it back by your expected growth:

FIRE number = annual expenses ÷ SWR
Coast number = FIRE number ÷ (1 + return)^years to retirement

The calculator also runs a month-by-month simulation with your current savings rate to find your coast date — the month your balance crosses the (steadily rising) coast threshold. And when your net worth is already at or above today's coast number, it says so plainly: you've coasted.

A worked example

You're 30, plan to retire at 65, and want to spend $40,000 a year ($3,333/mo) in retirement. At a 4% SWR the full goal is $1,000,000. At a 7% real return over 35 years, the coast number is 1,000,000 ÷ 1.07³⁵ ≈ $93,700. Hold that at 30 and you never have to save another retirement dollar. Wait until 50, though, and the same goal needs about $362,000 today — compounding is exponential in time, which is why coast numbers are shockingly small when you're young and unforgiving when you're not.

Honest caveats

Inflation. The 7% default is a real (after-inflation) return; keep expenses in today's dollars. Use a nominal return here and your coast number will be dangerously flattering.
Coasting is a bet on the average. A long stretch of below-average returns after you stop contributing has no new savings to paper over it. Many coasters keep saving a token amount as a buffer.
You still need income. Coast FIRE covers future-you. Present-you still pays rent, healthcare and groceries until retirement age.
The 4% rule assumes ~30-year retirements. Retiring earlier than 60? Consider a 3.25–3.75% SWR, which raises both numbers.
This is a planning estimate, not financial advice.

FAQ

Does Coast FIRE mean I can quit my job? No — it means you can stop saving, not stop earning. Every dollar you earn after coasting can be spent guilt-free, because retirement is already handled.

Why is my coast number so small? Time. At 7% real, money doubles roughly every decade, so 35 years of growth turns ~$94k into ~$1M without another contribution.

What if I'm already past my coast number? Congratulations — the calculator will tell you you've coasted. Anything you keep saving now just pulls your full FIRE date earlier.

More free calculators

FIRE Calculator — your FIRE number and projected retire-early date.
Lean FIRE vs Fat FIRE Calculator — compare two retirement budgets side by side.