Your FIRE number is simply your annual spending divided by your safe withdrawal rate — the pot size that, at a sustainable draw-down rate, can fund that spending indefinitely. At the classic 4% rule, that means 25× your annual spending. From there, this tool projects your current savings and monthly contributions forward at your expected return until they cross that number.
Spending $60,000 a year at a 4% withdrawal rate needs a $1,500,000 FIRE number. Starting from $50,000, saving 25% of an $80,000 income (about $1,667 a month) at a 7% return gets there in a bit under 25 years — and raising the savings rate to 40% cuts that meaningfully, since more of the growth comes from contributions early on, before compounding takes over.
The amount you'd need today such that, with zero further contributions, investment growth alone carries you to your FIRE number by a chosen retirement age. Once you've coasted past that number, every future dollar you save is optional — growth alone finishes the job.
A higher savings rate does two things at once: it grows your pot faster and shrinks the pot you actually need (since your target spending falls too). A higher return rate only does the first. That's why FIRE advice leans so heavily on the savings rate over chasing extra investment return.
The 4% rule comes from historical US market backtests (the Trinity study) over a roughly 30-year retirement. Longer retirements, non-US markets, or a desire for more safety margin argue for a lower rate (3–3.5%); shorter horizons or more flexibility in spending can support a higher one. It's a starting point, not a law.
No — this is a pre-tax projection in nominal (non-inflation-adjusted) future dollars, except where noted. Real-world results depend heavily on account type (taxable, tax-deferred, Roth) and your tax situation at withdrawal, which this tool doesn't model.