What Coast FIRE means in plain English

The idea in one paragraph

Coast FIRE is a milestone, not a quit-your-job button. It asks whether the savings you already have could grow—on their own, with no further retirement contributions—to your full FIRE number by a chosen retirement age. Until then you still need income for living costs. The Coast FIRE calculator turns that idea into a single “coast number” you can compare with today’s balance.

When to use

Open this when you already have invested savings and want one threshold: the balance that, with no new retirement contributions, is projected to reach your FIRE number by a chosen age. It fits if you are still earning and only asking whether future retirement contributions are still required for that path. It does not fit if you need a withdrawal you could start now, or if you are modeling monthly deposits—the Coast model leaves those out on purpose.

The formula in plain English

First you size the nest egg you would need at retirement (the FIRE number). Then you discount that target back to today, assuming annual compounding and zero future deposits:

FIRE number = annualExpenses ÷ (SWR / 100)
Coast number = FIRE number ÷ (1 + r)^yearsToRetirement
Projected balance at retirement = currentSavings × (1 + r)^years

annualExpenses is what you expect to spend in retirement. SWR is the safe withdrawal rate in percent (for example 4). r is the assumed annual return as a decimal. yearsToRetirement is how many years remain until your target age. The Coast model uses annual compounding and no contributions on purpose; it is intentionally simpler than the monthly growth model used on the regular FIRE tool.

A worked example

Suppose retirement spending is 40,000 a year and you use a 4% withdrawal rate. The FIRE number is 40,000 ÷ 0.04 = 1,000,000. With 25 years to retirement and a 6% assumed annual return, the coast number is about 1,000,000 ÷ (1.06)^25 ≈ 233,000. If your current invested savings are already above that coast number, the projection says Coast FIRE is achieved under those assumptions—and the same math projects today’s balance forward as currentSavings × (1.06)^25.

Change one lever at a time: a lower return, a later retirement age, or higher expenses moves the coast number more than a small tweak to today’s balance.

How to read the result

The coast number and the “achieved” flag are educational projections, not a personalized plan. Markets, inflation, fees, taxes, and sequence of returns sit outside the simple annual formula. Use the Coast FIRE calculator to stress-test optimistic and conservative returns with the same expenses and timeline. Remember: Coast FIRE does not mean you can stop earning today—only that, under the assumptions you entered, new retirement contributions may no longer be required for the nest-egg path.

Common mistakes

Reading “Coast achieved” as permission to stop working. Living costs until retirement still need income or other savings.

Pairing an optimistic withdrawal rate with an optimistic return. The coast number falls quickly when the assumed return is high. Run a lower return before you trust the flag.

Confusing this annual, zero-contribution model with the monthly FIRE calculator. They answer different questions on purpose.

Ignoring inflation because this educational version is nominal. A lower real-return assumption is the rough check. There is no hidden inflation toggle.

FAQ

Is Coast FIRE the same as being financially independent today?

No. Regular FIRE means the portfolio could support withdrawals now. Coast FIRE means existing assets are projected to reach the FIRE number by a future retirement age while you still cover living expenses from income or other savings.

Why does this calculator use annual compounding?

The Coast model keeps the threshold transparent: annual growth, zero future contributions. That differs intentionally from the monthly contribution growth model on the FIRE calculator, so the two tools answer different questions.

Does the projection include inflation?

Not in the current educational version. Figures are nominal. If you want a rougher inflation adjustment, try a lower real return assumption and compare results.

What return rate should I use?

There is no single correct rate. Historical averages vary by period and asset mix. Prefer conservative assumptions and run more than one scenario rather than anchoring on a single optimistic number.

Is this financial advice?

No. FinTools4U guides and calculators are for education and illustration only. They do not replace advice tailored to your tax situation, risk tolerance, or goals.

Related guides

• How compound interest actually works — growth with monthly contributions, which the Coast model leaves out.
• What your FIRE number means — the retirement target this coast number is discounted from.
• Debt snowball vs avalanche — if high-interest debt is competing with the savings you would otherwise leave to coast.

Try it with your figures

Open the Coast FIRE calculator, enter your expenses, SWR, years to retirement, assumed return, and current savings, then compare the coast number with today’s balance. If you want the same inputs tomorrow, use Save calculation on that page — no account required.