Lean FIRE Calculator
Find your Lean FIRE number from a frugal retirement budget and see how many years of saving it takes to reach financial independence, year by year.
Lean FIRE means reaching financial independence on a deliberately small budget — covering essentials like housing, food, insurance and transport, with little room for luxuries. Because the target scales with spending, a lean budget can cut years off the journey. This calculator turns your lean yearly budget into a FIRE number and shows how long your current savings rate takes to get there.
How to use this tool
- Enter your age and what you have invested now.
- Enter the lean yearly budget you would live on, in today's dollars.
- Enter how much you invest each year.
- Set an expected return after inflation and a withdrawal rate (4% is the usual starting point).
- Read your Lean FIRE number, the years it takes and the yearly path.
Formula
Target = yearly spending ÷ withdrawal rate
Years n = ln((T + C/g) ÷ (P + C/g)) ÷ ln(1 + g)
T is the target, P your current investments, C the amount you add at the end of each year and g the real (after-inflation) return. With a 0% return the years are simply (T − P) ÷ C. Working in real terms keeps every figure in today's dollars.
Example
A 30-year-old with $60,000 invested who would live on $36,000 a year needs $36,000 ÷ 4% = $900,000. Investing $24,000 a year at a 5% real return gets there in about 19.2 years, a little after age 49. Trimming the budget to $30,000 lowers the target to $750,000.
Frequently asked questions
How much spending counts as Lean FIRE?
There is no official threshold. In FIRE communities it usually means a budget well below the typical household's — often cited as under about $40,000 a year — but it depends on where you live and your household size.
Is 4% safe for an early retirement?
The 4% guideline was based on 30-year US retirements. Early retirees with 40–50 years ahead often use 3–3.5%, which raises the target. Try a lower rate to see the difference.
What does a lean budget leave out?
Lean plans have little buffer for health costs, home repairs or market slumps. Many people pair Lean FIRE with part-time income or a cash reserve.
This tool gives an estimate for general information only. It is not financial, tax, legal or medical advice — check with a qualified professional before you rely on the result.
Last updated: 2026-10-30