Free · Lean FIRE
Lean FIRE Calculator
Run the same Coast formulas with a frugal lifestyle budget — see how small the nest egg can get.
Lean FIRE calculator
Free — FIRE and Coast with a lower spending lifestyle.
Today's dollars
401(k), IRA, brokerage — exclude home equity
Affects years to coast and projected value, not the Coast number; set 0 to test if you've already hit Coast
Assumptions
Lean Coast number
$195,540
USD
You need $125,540 more to coast (36% funded).
Lean FIRE number
$687,500
Years to coast
7 yrs
You have
$70,000
Real return
3.88%
Projected value
$3M
Monthly spending
$10,055
Today's value
$3,741
How is Lean FIRE calculated?
Lean FIRE uses the same formulas as classic FIRE — with a lower annual spend.
Lean FIRE nest egg ≈ lean annual spend ÷ SWR · Coast = nest egg ÷ (1 + real return)^years
- Set a frugal retirement spend (this page seeds a lower default).
- Pick SWR and return/inflation assumptions.
- Read Lean FIRE nest egg and today’s Coast checkpoint.
For a richer lifestyle path: Fat FIRE calculator.
Related calculators
Same engine — different lifestyle assumptions.
Lean FIRE notes
Lean is a planning dial, not a life sentence
A lean spend is useful for early stress tests. Re-run Coast or Fat when lifestyle costs rise.
Guides
Formulas and path comparisons.
Lean FIRE calculator FAQ
What is a lean FIRE calculator?
- A FIRE calculator seeded for lower annual spending so you can see the nest egg and Coast number for a frugal retirement lifestyle.
How is Lean different from Fat FIRE?
- Same formulas — Lean uses a lower spend, Fat a higher one. Both pages sit on WorthCay for side-by-side comparison.