What is Lean FIRE?
Lean FIRE is Regular FIRE aimed at a minimal, intentional budget. The math is identical — it's the spending assumption that's different. By keeping ongoing costs low, the portfolio needed to cover them is smaller too, which usually means reaching financial independence faster than someone spending more freely.
This calculator uses the same nominal approach as Regular FIRE: your portfolio grows at your expected investment return (10% by default), and only your everyday lifestyle spending rises with prices each year — a fixed mortgage repayment doesn't inflate, since it's already a fixed amount.
How to use this calculator
Use it exactly like the Regular FIRE calculator — enter your total annual spending, invested assets, monthly investment amount, and current age. For Lean FIRE, that spending figure is typically toward the lower end: a tighter, more intentional budget rather than a "keep every luxury" number. If part of your spending is a mortgage, add the monthly repayment and years remaining separately, since that payment won't rise with inflation the way the rest of your spending will.
What is the 4% rule?
The 4% rule works the same way here as anywhere else: divide your annual spending by 4% (or multiply by 25) for a rough FIRE number. Because Lean FIRE spending is lower, the resulting number is smaller — but a leaner budget also leaves less room to absorb a bad run of markets early in retirement, so some lean retirees choose a more conservative withdrawal rate. You can adjust it in the advanced settings between 2.5% and 6%.
Lean FIRE vs Regular FIRE
Lean FIRE isn't a different formula — it's Regular FIRE with a smaller spending target. Strategies like geographic arbitrage (living somewhere with a lower cost of living) and deliberately minimal living are common ways to make the numbers work without sacrificing what actually matters to you.
Frequently asked questions
Is Lean FIRE riskier than Regular FIRE? A tighter budget leaves less slack if costs rise unexpectedly, so it's worth building in some buffer or keeping withdrawal rate assumptions conservative.
Can I upgrade from Lean to Regular FIRE later? Yes — nothing stops you from continuing to invest past your Lean number if your spending grows or you want more of a cushion.
What's a typical Lean FIRE budget? There's no fixed figure — it's whatever a stripped-back, deliberate version of your lifestyle costs. Enter your own number rather than relying on a preset amount.
Does this calculator account for tax? Yes, there's an optional tax slider on withdrawals, set to 0% by default. When it's above zero, the calculator shows how much of each withdrawal you actually keep.
What if I have a mortgage? Enter the monthly repayment and years remaining separately from your other spending. It's treated as a fixed nominal payment that doesn't rise with inflation, and drops off your required spending once it's paid off.
Why does my FIRE number look bigger than other calculators? By default, results are shown in future dollars — the actual amount your portfolio will be worth by the time you retire, after years of inflation. You can switch to today's dollars in the "Why does this look different?" expandable on the FIRE number card; either way, the retirement date it points to is the same.