How this is calculated
FIRE number = yearly spending × 25; timeline: compound (income − spending) ÷ 12 monthly at the real return until the target
FIRE combines two ideas: the 4% rule (a portfolio of ~25× your annual spending can sustainably fund it) and the observation that your savings rate alone roughly fixes the timeline. Save 10% of income and financial independence sits ~50 working years away; save 50% and it's ~17; save 70% and it's under 10. Salary barely appears in that arithmetic — because a higher income only shortens the path if the spending doesn't rise to meet it.
The simulation compounds your current investments plus the monthly gap between income and spending, at a real (inflation-adjusted) return, until the balance crosses 25× spending. Using real returns keeps everything in today's dollars: the FIRE number you see buys what that money buys now.
Reaching the number doesn't obligate anyone to quit — most people discover the countdown itself changes their relationship with work. Optional work negotiated from a full portfolio is a different job than mandatory work negotiated from a paycheck. FIRE's fine print (healthcare before pension age, sequence-of-returns risk, flexible withdrawal in bad years) deserves real reading before any resignation letter.
Frequently asked questions
What savings rate do I need?
The classic table (5% real returns, starting from zero): 10% ≈ 51 years, 25% ≈ 32 years, 50% ≈ 17 years, 65% ≈ 10.5 years. Your existing investments shorten these — the tool accounts for them.
Why 25× spending?
It's the inverse of the 4% safe withdrawal rate from the Trinity-study research line. More conservative planners use 28-30× (a 3.3-3.6% withdrawal), which you can model by mentally scaling the target.
Real vs nominal returns — which do I enter?
Real (after inflation), so the answer stays in today's purchasing power. Long-run stock returns of ~10% nominal correspond to ~6-7% real; 5% is a moderately conservative default.
Does FIRE require extreme frugality?
It requires a gap between income and spending — how you create it is yours. Plenty of paths run through income growth with flat lifestyle rather than austerity. The math is indifferent; it only sees the rate.