Your FIRE number is the portfolio size at which work becomes optional: invested assets that can fund your spending indefinitely. This FIRE retirement calculator gives you the number, lean and fat variants, and, with your current savings rate, your estimated FIRE date.
Sources & assumptions: the withdrawal-rate convention comes from William Bengen's 1994 paper “Determining Withdrawal Rates Using Historical Data” and the 1998 Trinity Study (Cooley, Hubbard & Walz), which tested inflation-adjusted withdrawals against US market history since 1926. The default 6% real return is a planning assumption, long-run US equity real returns have historically averaged roughly 6–7% per year (Dimson, Marsh & Staunton, Credit Suisse Global Investment Returns Yearbook), adjust it to your own outlook. Everything is in today's dollars; taxes, fees and sequence-of-returns risk are not modeled. All math runs in your browser and nothing you type leaves your device.
| Input | Result |
|---|---|
| $40k/yr spending, 4% rule | $1,000,000 (lean $750,000 · fat $1,500,000) |
| $100k invested + $3,000/month at 6% | Full FIRE in 13.8 years |
| $500k + $2,000/month, $50k spending at 3.5% | Target $1,428,571 · FIRE in 11.8 years |
Your FIRE number is the invested portfolio at which you are financially independent: it can fund your annual spending indefinitely at a sustainable withdrawal rate, so paid work becomes optional. It is the single most-tracked number in the FIRE (Financial Independence, Retire Early) movement.
A planning convention from William Bengen's 1994 research and the 1998 Trinity Study: withdraw 4% of the portfolio in year one of retirement, adjust for inflation each year, and historically the money survived virtually every 30-year period since 1926. Inverted, it says you need 25× annual spending, the classic '25x rule'.
For a traditional ~30-year retirement, 4% is the historical benchmark. For early retirements of 40–50+ years, many planners choose 3.25–3.5% to withstand longer horizons and bad return sequences, the calculator accepts any rate so you can compare.
Lean FIRE is retiring on a stripped-down budget, here estimated at 25% less spending, which shrinks the number proportionally. Fat FIRE is retiring with a cushier budget, here 50% more spending. Most people land between the two.
Yes, by working in today's dollars: use a real (after-inflation) return, the default is 6%, and enter spending in today's prices. The FIRE number you get is in today's purchasing power.
The "multiply spending by 25" convention is the inverse of a 4% first-year withdrawal rate, which traces to William Bengen's 1994 analysis of every rolling retirement window since 1926 and was stress-tested by the 1998 Trinity Study. Both found a stock-heavy portfolio historically survived 30 years at that rate. Two honest caveats: the studies cover 30-year retirements, while early retirees need 40–50 years (a 3.25–3.5% rate, a 28–30× multiple, is the common adjustment), and the rule is a planning convention, not a guarantee; it assumes you actually hold a diversified portfolio rather than cash.
| Variant | Annual spending it funds | Number at 4% | The real trade-off |
|---|---|---|---|
| Lean FIRE | ~$30,000–40,000 | $750k–$1m | Least slack: one bad health year or car breaks the budget |
| Regular FIRE | ~$50,000–70,000 | $1.25m–$1.75m | The classic benchmark most plans target |
| Fat FIRE | $100,000+ | $2.5m+ | Largest number, longest accumulation, often 10+ extra years |
Run your own spending number through the calculator rather than borrowing anyone else's: the multiple is arithmetic, but the spending it multiplies is your life.
How this page is built and kept current. Written and fact-checked by the MoneyCalcsHub editorial team. We do not sell financial products and we accept no payment to change a result, the arithmetic on this page runs in your own browser from the numbers you type.
Official sources used on this page:
Source-dependent figures are reviewed when the cited issuer publishes an update. Worked examples show the formula applied to the listed inputs; interactive results are calculated in your browser.
Spotted an error? Write to [email protected], corrections are published on the page and the last-updated date changes with them. Full process: editorial policy.