Are you Lean FIRE — and what's your number?

Lean FIRE is financial independence on a frugal, intentional budget — the leanest, earliest exit on the FIRE spectrum. It sits below regular FIRE and Chubby FIRE: full independence, reached soonest, on the tightest budget of the four tiers. In practice it means a household living on roughly $25,000 to $40,000 a year, backed by a portfolio of about $625k to $1M.

The confusing part is that nobody agrees on the band. You'll find Lean defined as anything under $40k of spending, sometimes pinned to $25k–$40k, sometimes tied to below-median or near-poverty-line budgets; net-worth targets range from $500k to $1.2M. That ambiguity is exactly why the calculator above leads with a clear answer: type your spending, and it resolves both questions at once — are you Lean, and what's your number?

FIRE isn't one finish line — it's a spectrum of how much you spend in retirement, and therefore how big a portfolio you need. Lean is the frugal floor: the smallest number, reached soonest, in exchange for the tightest budget.

Lean is what financial independence looks like when you optimize hard for freedom over spending. The natural step up, Lean vs Chubby, is below.

There's only one formula, and it's the same 25× rule behind every flavor of FIRE — your annual spending divided by a safe withdrawal rate:

To get the date, project what you have invested forward at your expected return, adding your annual contribution each year, until the balance reaches that number:

At a 4% withdrawal rate, a Lean budget lands between $625k and $1M ($25k–$40k of spending × 25). Want a longer safety margin? A 3.5% rate — the long-horizon convention for someone retiring in their 30s or 40s with a 40+ year runway — lifts the same band to roughly $714k–$1.14M (× 28.6). The toggle on the calculator switches between the two live.

Geographic arbitrage is Lean's lever. Many Lean FIRE households shrink their number by moving somewhere cheaper — a lower cost of living drops your spending, and your spending is your number. Cut $8k a year off your budget and you've cut $200k off the target you need to hit.

Single vs. couple. The number is driven by spending, not headcount — so a couple spending $38k together needs the same $950k as a solo spender at $38k. Lean is genuinely tight for two: holding combined spending under $40k takes real frugality. But two incomes tend to reach the number years sooner.

This is the trade-off that actually decides your plan, because it's a choice between time and comfort. Lean FIRE buys freedom soonest: a smaller number, reached years earlier, in exchange for a budget that stays deliberately tight — you watch the grocery bill and a big surprise expense stings. Chubby FIRE is the comfortable middle: nice travel, a paid-off house, no anxiety about a restaurant bill — but a number two to four times larger and years more of saving.

The gap is enormous in time, not just dollars. Moving your target spending from $38k to $120k roughly triples the number on the same savings — which is why Lean FIRE is the fastest route out, and why its whole discipline is keeping spending genuinely low.

It fits people who value time and freedom over spending and can happily live on a frugal budget — optimizers who would rather be out in ten years on $38k than in twenty-five on $120k. It rewards low-overhead lives: geographic arbitrage, no-debt living, finding genuine contentment well below the median budget.

It's a weaker fit if your real life genuinely needs a bigger budget (don't under-target and white-knuckle it), or if you can't move somewhere cheaper and your costs are fixed high. And the standard caveat applies hardest here: sequence-of-returns risk — a market crash in your first few retired years does outsized damage — bites a lean, early, decades-long runway most of all, which is exactly why a 3.5% rate, a cash buffer, or a little flexible income is worth considering.