Lean vs Fat FIRE Calculator

They’re the same FIRE idea pegged to three different lifestyles. Lean FIRE is a bare-bones budget — financial independence on minimal spending, often under $40,000 a year, which means a smaller nest egg you reach sooner. Regular (or just “FIRE”) is independence on your normal spending. Fat FIRE is a comfortable, no-compromises budget — six figures a year for many — which needs a much larger nest egg and more time. This calculator lines all three up so you can see the trade-off in numbers, not vibes.

Each tier’s number is its annual spending divided by your safe withdrawal rate — the 4% rule, which is the same as 25× spending. Spend $30,000 a year in Lean mode and you need $750,000; $50,000 of Regular spending needs $1,250,000; $100,000 of Fat spending needs $2,500,000. A more conservative 3.5% rate raises every number (about 28.6× spending), and a more aggressive 5% lowers them (20×).

Because the targets compound against your savings rate. Fat FIRE’s nest egg might be three or four times Lean’s, but the extra years it takes are amplified by the fact that you’re reaching for a much bigger number with the same monthly contribution. The last stretch is the slowest, since each additional dollar of target sits at the top of the curve where growth has to do the heavy lifting. The gap between Lean and Fat — often a decade or more — is the real cost of a richer retirement.

The retirement / FIRE calculator solves a single target: you pick one spending level and it tells you the years to that one number. This calculator runs three lifestyle tiers at once and stacks the results side by side, so the comparison itself is the answer. Use the single calculator when you know your target; use this one when you’re deciding how lean or how fat you want your independence to be.

Use real budgets, not round numbers. For Lean, strip your spending to essentials — housing, food, healthcare, insurance — the version of your life you could live indefinitely without feeling deprived. For Regular, use your actual current annual spending. For Fat, add the things you’d want with no money stress: more travel, a bigger home, generosity, a cushion for healthcare. The three FIRE numbers are only as honest as the budgets behind them.

Real — returns after inflation, so every figure is in today’s dollars. Your spending tiers are in today’s money, so we grow your savings at a real return (roughly a long-run ~7%, which is ~10% nominal minus ~3% inflation) and compare like with like. That keeps the FIRE numbers meaningful without a separate inflation adjustment. As with any projection, treat the years as planning estimates: real markets vary, and the order of returns matters near the finish line.