Lean FIRE calculator
The smallest number and the earliest exit — because spending less cuts what you need twice over. It also leaves the least room for anything to go wrong.
To live on $40,000 a year, you need
$1,000,000
That is 25× your annual spending, at a 4% withdrawal rate. On the common labels, $40,000 a year is usually called Lean FIRE.
These cut-offs are conventions the community uses loosely — there is no standard definition, and different groups draw the lines in different places. Treat them as vocabulary, not thresholds you have to hit.
Spending is taken at face value — if tax or health cover is not already inside your figure, your real target is higher.
Why spending is the strongest lever there is
Cutting what you spend works on both ends of the problem at once. You free up more to invest each year, and you shrink the target that money has to reach. Nothing else in the equation does both.
At a 4% withdrawal rate, every $1,000 a year you take off your spending takes $25,000 off the portfolio you need. That is why Lean FIRE arrives first — not because its adherents invest better, but because they moved the one input that counts twice.
The thing a lean plan spends first: margin
The maths is identical to every other version of FIRE. What is different is what happens when the plan meets a bad year.
40%
of a $40,000 budget is what an unsubsidised benchmark health plan can cost at 60
That benchmark is about $15,914 a year for a 60-year-old earning $65,000, assuming the enhanced premium tax credits stay lapsed ($10,389 of it is the increase since they did — KFF, US only, as of July 2026; the figure is age-rated and a 45-year-old pays materially less). Against a lean budget it is not a line item, it is two-fifths of the plan.
The same logic applies to every shock: a roof, a car, a family emergency. A larger budget absorbs those by trimming discretionary spending for a while. A lean budget has already done the trimming — that is what made it lean.
None of which makes Lean FIRE wrong. It makes flexibility the thing to protect deliberately, because it is the safety valve no withdrawal-rate model captures.
Common questions about Lean FIRE
- What is Lean FIRE?
- Lean FIRE is early retirement on a deliberately low spending level. Because your target is annual spending divided by your withdrawal rate, cutting what you spend cuts what you need twice over: you save more each year and you need less at the end. It produces the smallest number and the earliest exit of any version of FIRE.
- How much do you need for Lean FIRE?
- There is no official cut-off. The label is commonly used for household spending under roughly $50,000 a year, which at a 4% withdrawal rate is a portfolio around $1.25m or less. The community draws this line in several different places, so the number that matters is yours, not the convention.
- What's the catch with Lean FIRE?
- Margin. A lean budget has less discretionary spending to cut when something goes wrong, so the same shock takes a bigger proportional bite. Health cover is the clearest example: an unsubsidised benchmark plan can run around $15,914 a year for a 60-year-old, which against a $40,000 budget is two-fifths of everything you planned to spend.
- Is Lean FIRE risky?
- It concentrates the risk rather than removing it. The maths works exactly the same way as any other version. What differs is that flexibility — the ability to spend less for a couple of bad years — is the safety valve a fixed withdrawal rate never models, and a lean plan has already used most of it up before it starts.
The other levels: Chubby FIRE · Fat FIRE · Barista FIRE