Lean, Coast, Barista, Fat — the four FIRE numbers, and which one is yours

Ask most people for their "FIRE number" and they will quote you a single figure. Twenty-five times annual expenses. A million, two million, whatever the lifestyle costs multiplied by some tidy round multiple. It feels precise, which is exactly the problem. That single number answers a question most people have not actually asked themselves yet.

Because there isn't one FIRE number. There are four, and they are not four flavours of the same idea — they are four genuinely different math problems, each one quietly changing a different term in the same underlying equation. Lean, Coast, Barista and Fat get talked about as *lifestyles*, as if the choice were between rice and beans or something expensive on a balcony. That framing misses what is actually going on. The lifestyle is the output. The math is the input, and the math is where the decision really lives.

The chassis: one equation, four ways to bend it

Every FIRE number on earth is a version of this:

Target number = Annual expenses × Multiple,   where Multiple = 1 ÷ safe withdrawal rate

The famous "4% rule" is just a way of saying the multiple is 25, because one divided by 0.04 is 25. It traces back to William Bengen, who in 1994 found a retiree could withdraw 4% in year one, adjust for inflation each year after, and reliably make the money last about three decades; the 1998 Trinity Study reached a similar conclusion, and "25× your spending" became folklore. (We pull that history apart in the 4% rule, revisited.)

Here is the part that has quietly moved on. Bengen himself has revised the figure: in his 2025 book he puts the worst-case safe starting rate (his SAFEMAX) at 4.7% rather than 4%, after broadening the asset mix, and has suggested 5.25–5.5% in many historical conditions with an average closer to 7%. Pulling the other way, Morningstar's forward-looking research landed on 3.9% as the optimal starting rate for someone retiring in 2026, having recommended as little as 3.3% a few years earlier. So the honest version of the "rule" is a range — roughly 3.9% to 4.7%, with 4% a convenient anchor.

For early retirees the range tilts conservative, for a specific reason. Bengen's headline numbers assume a 30-year retirement. Stretch that to 50 years — what retiring at 40 implies — and even Bengen's figure drops to around 4.2%; many in the FIRE community deliberately use 3.25–3.5% for margin. The villain is sequence-of-returns risk: a bad run of markets in the first few years, while you are also pulling money out, does permanent damage an identical run later would not. A longer horizon means more chances to meet that villain early.

Portfolio survival under different withdrawal rates

That table is worth pausing on. The same person, with the same 40,000 of annual spending, has a target anywhere from 727,000 to 1.33 million depending *only* on the withdrawal rate they choose. That is a 600,000 swing and not a single thing about their actual life has changed. The multiple is a confidence dial, not a fact.

Now, the four archetypes — four edits to that base equation. Three change an input; one changes the structure entirely.

Hold onto that last distinction — Coast is the only archetype that changes the *shape* of the equation rather than its inputs. It is the most useful idea in this article and we will come back to it.

Lean FIRE: the subtraction problem

Lean FIRE is the expense side of the equation taken seriously. You do not touch the multiple, add income, or bend time. You just spend less — and because the target is your spending × 25, every unit you cut out of your annual budget removes 25 units from the mountain.

That multiplier is the entire point. Trim 1,000 off yearly spending and you shave 25,000 off your target. Live on 24,000 instead of 40,000 and your number drops from a million to 600,000. You have not earned more, invested more cleverly, or waited longer — you have simply moved the finish line toward you, 25 steps for every one step you take.

Read the left column in whatever currency you spend in: the multiple is dimensionless, so 25× behaves identically in dollars, rupees, pounds or euros. Only purchasing power differs, and that is already baked into your own expense figure.

How the target scales with spending

Lean FIRE suits people for whom a modest, deliberate life is a preference, not a sacrifice — the fastest way to need less money is to need less money. The honest risk, plainly, is the missing buffer. A lean budget has little slack, and a portfolio sized to it has little slack either. The same 25× leverage works against you on the way back up: every 1,000 your real expenses creep upward is another 25,000 you suddenly needed and do not have. Lean FIRE rewards people who genuinely prefer less, and punishes those who only thought they did.

Fat FIRE: the multiplication problem, with a twist

Fat FIRE is the same equation pointed the other way, with a second move most descriptions skip. The obvious move is to raise expenses: a comfortable life, travel, a nice home, generosity. At 100,000 of spending you are looking at 2.5 million at 4%, and the 25× multiplier is just as merciless on the way up as it was generous on the way down.

The twist is the multiple itself. Fat-FIRE seekers often *raise* it by choosing a lower, more conservative withdrawal rate — because the point of a fat number is durability, and a longer horizon argues for a smaller slice. So Fat FIRE is frequently a *double* edit: bigger expenses and a bigger multiple, and they compound.

Same lifestyle, but choosing 3.25% over 4.0% adds roughly 577,000 to the target. The lifestyle did not get fancier; the safety margin got wider.

Fat FIRE suits high earners who can fund a large number without postponing the exit into their seventies. The trap, plainly, is that the goalposts move. Lifestyle expands to fill the number you give it, so "comfortable" at 35 becomes the baseline by 45, and the target drifts up to chase it. This is how "one more year" syndrome is born. The discipline Fat FIRE demands is not earning — it is deciding, once and firmly, what "enough" means and refusing to renegotiate it every time the portfolio grows.

Coast FIRE: the time problem

Here is the archetype that is genuinely different. Lean, Fat and Barista keep the structure and change what you plug in. Coast FIRE changes the structure: it adds a new operation — time.

Instead of "what portfolio do I need to live off?", Coast FIRE asks "what amount do I need invested *today* so that, if I never add another dollar, compounding alone carries it to my full number by traditional retirement age?" You are solving for the seed, not the destination:

Coast number today = Full FIRE number ÷ (1 + r)ⁿ

where *r* is your expected real (after-inflation) return and *n* is the years until you actually retire. The full number is in today's money and the return is real, which keeps inflation consistent on both sides. Suppose your full number is 1 million in today's money, you are 32, and you mean to retire at 62 (n = 30). At a 5% real return, 1 million ÷ 1.05³⁰ ≈ 1,000,000 ÷ 4.32 ≈ 231,000. Get 231,000 invested by 32 and stop saving entirely, and on those assumptions you reach a million by 62 without contributing another cent. Compounding does the remaining 769,000 of work.

The Coast curve — saving stops, time finishes the job

(Seed needed today for a 1,000,000 target. These scale linearly: for a 1.5 million target, multiply every cell by 1.5.) Look at the spread: at 35 years and 7% real, the seed is about 94,000; at 10 years and 4% real, it is 676,000 — more than seven times larger for the identical destination. Two variables dominate Coast FIRE: how young you start, and what return you assume. Time does the heavy lifting, which is why this archetype is devastatingly effective for the young and weak for the impatient.

Coast FIRE suits people who front-loaded their saving and now want to stop sprinting — freedom *from saving* rather than *from working*. The risks are specific: the return assumption is the whole engine (4% vs 7% is the difference between a comfortable plan and a heroic one), the seed does not feed you (you still cover living costs through your working years), and the long horizon that makes it powerful also makes it slow to correct if the early years disappoint.

Barista FIRE: the offset problem

Barista FIRE is the equation with an income stream subtracted from the expense side. Your portfolio no longer covers everything — only the gap between what you spend and what you keep earning through part-time or lighter work:

Barista number = (Annual expenses − part-time income) × Multiple

The symmetry is lovely: a unit of reliable ongoing income does exactly what a unit of cut expense did in Lean FIRE. Both shrink the gap the portfolio funds, and both reduce your target by the multiple — 25 units of portfolio for every 1 unit of annual income. Earning 15,000 part-time has the same effect on your number as cutting 15,000 of spending. One asks you to want less; the other asks you to keep working a little. Which is easier is entirely a question about you.

At 20,000 of income — exactly half of spending — the target halves to 500,000. Each unit of dependable income removes 25 units from the number, identical to cutting an expense.

Barista FIRE suits people who would rather step back than step out — keep one foot in some kind of work rather than save another decade to fund total idleness. It is the archetype for people who do not want to *stop working*; they want to *stop having to*. I think it is the most underrated of the four, because it quietly solves the problem the others struggle with: it dramatically lowers the portfolio you need while keeping income, structure and benefits in play, without the austerity of Lean or the heroic accumulation of Fat. The risks are real — it leans on your continued ability and willingness to work, and part-time income is less stable and less inflation-protected than the salary you left. The income you subtract is an assumption too, and it deserves the same scepticism as Coast FIRE's return assumption.

They are not four doors. They are one staircase.

The most common mistake is treating these as four separate destinations you pick between, like meals off a menu. They overlap, they stack, and two of them are *stages* rather than endpoints.

Coast FIRE is a milestone, not a finish line. The moment your invested assets cross your Coast number, you have reached it — regardless of which final number you aim at. You can be Coast FIRE on the road to a Lean target or a Fat one. Barista FIRE is a bridge — often the span between "enough to stop saving" and "enough to stop entirely," letting part-time income carry you across while the portfolio compounds untouched. Lean and Fat are genuine destinations — the size of the life your portfolio fully funds with no further work.

So the cleaner model is a sequence: you Coast first (time takes over saving), you may Barista next (part-time income bridges the gap), and you arrive at a fully-funded number somewhere on the spectrum from Lean to Fat. They are floors of the same building, not four buildings.

How the four archetypes nest

Which one is yours?

The right archetype falls out of a handful of facts about your situation, not your aspirations. Work through these.

How much time do you have? Young, with decades to go? Coast FIRE is extraordinarily powerful and you may be closer than you think. Older, short horizon? Coast loses its magic and you are choosing among the destination numbers.

How much have you already invested? Compare your current invested assets to your Coast number. Past it — you have won the saving game; now decide whether to Barista the rest or keep working by choice. Far below — you are still in pure accumulation.

How flexible is your spending, honestly? If a modest life is a genuine preference, Lean is on the table. If comfort matters to you, do not build a Lean plan you will resent and abandon. The 25× multiplier makes self-deception expensive in both directions.

How do you feel about work itself? Never want to work again — you need a full destination number, Lean or Fat. Happy to do something lighter — Barista slashes the number you need.

What is your tolerance for assumptions? Coast leans on return assumptions; Barista on income assumptions; Lean on expenses staying low; Fat on actually accumulating a large sum. Pick the bet you are most comfortable losing a little on.

A few opinions, plainly: most people overestimate how Fat their number needs to be and underestimate how powerful Coast is when young — exactly backwards from what serves them. Lean's real danger is the thin buffer, not the austerity. And Barista is the quiet winner for more people than admit it, because "I want to stop *having* to work" is a far more common true desire than "I want to never work again."

The fine print, which is not optional

Everything above is a model, and models are simplifications wearing confident clothing. Inflation is assumed to behave and does not always — a bad inflationary stretch is hardest on the leanest plans. Sequence-of-returns risk is real and is why early retirees should lean to lower rates. Taxes are in none of these equations and should be in yours, because what you can spend is what is left after tax. Healthcare is a wildcard whose weight depends entirely on where you live, and it is the hidden engine behind the US version of Barista FIRE. And every figure here is an estimate drawn from the past, offered with humility, not a guarantee about your future.

None of this is personalised financial advice. The figures are illustrative and currency-neutral, chosen to make the math legible rather than to fit your life. Run your own with the FIRE calculator and the Coast FIRE calculator, and set the rate honestly with the safe-withdrawal-rate calculator.

The point

There is no such thing as "the" FIRE number, and chasing one is how people end up with a target that fits a stranger's life rather than their own. There are four, and each answers a different question. Lean asks how little you are content to spend. Fat asks how much comfort you want to fully fund. Barista asks how much you would happily keep earning. And Coast asks how much time you have for compounding to do the work you would otherwise have to.

Pick the question that is actually yours, and the number stops being a mystery and becomes arithmetic. That is the whole trick. The math was never the hard part — knowing which equation you are solving is.