Coast FIRE calculator

How the formula works

Coast FIRE asks a narrower question than early retirement: how much would I need invested today so that, with no further contributions at all, compounding alone delivers a full retirement pot by my retirement age? Past that number you still work — you just no longer have to save.

It takes two steps. First, the full retirement pot — the FIRE number — comes from the safe withdrawal rate: the fraction of the pot you plan to draw each year. A 4% rate means the pot is 25 times annual spending:

Second, discount that pot back to today at the real return \(r\), over the \(n\) years until retirement — the reverse of compound growth:

If you are not there yet, note that the target does not sit still. Every year you wait leaves one fewer year for compounding to do the work, so the coast number at any future age is higher:

The calculator projects your balance forward — current savings plus end-of-month contributions at the effective monthly rate \((1+r)^{1/12}-1\) — and finds the first month it crosses that rising curve. That crossing is your coast age.

Why the return is a real return. Every dollar figure here is in today's purchasing power: the spending you enter is today's spending, and the FIRE number is 25× today's spending. For the arithmetic to stay consistent, the growth rate must also be measured in today's dollars — the return after inflation. If you discounted a today's-dollars target at a nominal 8%, you would be claiming inflation's share of the growth as your own, and the coast number would come out far too low. Long-run stock returns of roughly 8–10% nominal correspond to about 5–7% real; using the real figure means the answer never needs an inflation adjustment — it is already in money you understand.

What each input means

Current age & retirement age

Their difference \(n\) is the runway compounding gets to work with. It is the most powerful input on the page: each extra year divides the coast number by another \((1+r)\).

Invested so far

What is in your retirement-purposed accounts today — 401(k), IRA, taxable brokerage. Not your emergency fund or house equity: only money that will stay invested until retirement.

Annual spending in retirement — today's dollars

What a year of your retired life costs at today's prices. Working in real terms means you never have to guess what groceries cost in 2063 — the model keeps everything in today's purchasing power.

Expected real return — \(r\)

Your assumed investment return after subtracting inflation. The default 5% corresponds to roughly an 8% nominal return with 3% inflation — in the neighborhood of long-run stock-heavy portfolio history, and nothing like a guarantee. The questions below discuss what is reasonable.

Safe withdrawal rate — SWR

The share of the pot you plan to draw each year in retirement. 4% is the classic rule-of-thumb (25× spending); 3.5% is more conservative (≈28.6×) and raises every number on the page accordingly.

Monthly contribution while still saving

What you are putting away now, used only to project when you reach your coast number — it does not change the coast number itself.

A worked example

The worksheet's defaults: age 28, retiring at 65, with $45,000 invested, spending $50,000 a year in today's dollars, a 5% real return and a 4% withdrawal rate.

• The FIRE number: $50,000 / 0.04 = $1,250,000 — 25 years of spending, in today's dollars.
• There are \(n = 37\) years to retirement, and \(1.05^{37} = 6.08\). The coast number today: $1,250,000 / 6.08 = $205,545. Have that at 28 and compounding alone finishes the job.
• With $45,000 invested, progress is $45,000 / $205,545 = 22%. Left alone, today's $45,000 grows to $273,663 by 65 — enough to support about $10,947 a year of spending, not $50,000.
• At $800 a month the balance grows faster than the target does, and the projection has them crossing at age 62.9 — from there, $1,129,186 compounds to the full $1,250,000 by 65 without another deposit.

That late crossing is worth staring at: $800 a month is close to what this plan needs for a 65-year-old's retirement, so coast arrives only a couple of years early. A larger contribution, a smaller spending target or a later start each move the crossing — the worksheet recomputes all of it live.

Assumptions and limits

• The real return is constant. Markets deliver averages through swings, and a bad decade early on means compounding has less to work with — the model has no volatility and no sequence-of-returns risk in it.
• The safe withdrawal rate is a planning heuristic, not a law. The 4% figure comes from historical 30-year US retirements; longer retirements and different markets argue for lower rates. It sets the target; it does not guarantee the target suffices.
• Taxes and account access are ignored. Money in a 401(k) or IRA generally cannot be touched before 59½ without penalty (SEPP rules and Roth conversion ladders are the workarounds), and withdrawals may be taxed — the pot you need is measured before those frictions.
• “Stop saving” does not mean stop working: past your coast number you still need income to cover today's living costs — just not to fund retirement on top of them.
• This is arithmetic on your assumptions, not advice. It shows what the inputs imply; it cannot know what markets will return.

Questions people ask

What's the difference between FIRE, Coast FIRE and Barista FIRE?

FIRE — financial independence, retire early — means the full pot: investments large enough to fund all your spending at your withdrawal rate, so work becomes optional now. Coast FIRE is the earlier milestone this page computes: enough invested that compounding alone reaches the full pot by your normal retirement age, so you can stop saving but keep earning your living. Barista FIRE sits between them — enough invested to draw some income now, with part-time work (the proverbial barista job, often kept for health insurance) covering the rest. Same arithmetic, different finish lines.

What real return is reasonable to assume?

US stocks have returned roughly 6–7% a year after inflation over the long run, and a diversified stock-heavy portfolio somewhat less after fees and any bond allocation — which is why 4–5% real is a common planning assumption and this page defaults to 5%. The honest answer is that nobody knows the next 37 years; run the worksheet at 4% and at 6% and treat the spread between the answers as the uncertainty, not the midpoint as a promise. A lower assumption raises the coast number and is the safer way to be wrong.

What if I keep contributing after reaching my coast number?

You retire on more, or earlier. On the defaults the projection reaches coast at age 62.9; stopping contributions cold there still compounds to $1,250,446 by 65 — about $50,018 a year at a 4% withdrawal rate — while continuing the $800 a month to 65 grows the pot to $1,271,455, supporting about $50,858. Coast is a floor, not a ceiling: every dollar past it buys margin against the return assumption being too rosy, or moves the retirement date up.

Is 4% safe over a 30-plus-year retirement?

The 4% rule was derived from historical 30-year US retirements, and even there it failed in the worst starting years — it is a rule of thumb with roughly a 95% historical success rate, not a guarantee. Someone coasting toward a retirement that could run 40 years has a real case for 3.5% or lower, which raises the target from 25× spending to about 28.6× and raises the coast number by the same proportion. The worksheet takes any rate; the cautious move is to plan at a lower one and let 4% be the upside case.

Does this account for Social Security?

No. The model funds all of your retirement spending from the portfolio, as if Social Security paid nothing. For most American workers it will in fact replace a meaningful slice of spending, which makes the coast number here deliberately conservative — a buffer against benefit changes, early claiming reductions and the return assumption itself. If you want to count it, subtract your expected annual benefit from the spending input and the whole page rescales accordingly.