FIRE Calculator

You're earning $90K, saving $30K a year, and want to know when you can stop working. The 4% rule says you need 25× your annual expenses invested. If you spend $40K/year, that's $1M. Plug in your numbers and see the projected year you cross that line.

The calculator handles current savings, monthly contributions, expected return rate, and target annual expenses. Adjusting the savings rate by 5 percentage points usually shifts the FIRE date by 3–5 years — which is wild but accurate, because higher savings means lower required nest egg AND faster accumulation.

Doesn't model taxes on withdrawal, which matters for traditional retirement accounts. Treat the result as a target, not a guaranteed date.

The math behind the calculator is the future-value-of-annuity formula combined with the 4% rule. The accumulation phase computes: FV = current savings × (1+r)^n + monthly contribution × [((1+r)^n − 1) / r], where r is the monthly real return rate and n is months. Then the FIRE target is set at 25× annual expenses, which is the inverse of the 4% withdrawal rate. The calculator finds the year where projected FV first exceeds 25× expenses — that's your FIRE date.

A worked example: you're 30, have $40K saved, contribute $30K annually, expect 7% real returns, and target $40K annual expenses. Your FIRE number is $1,000,000. Plugging into the formula: at 7% real, $30K/year contributions plus $40K starting balance reach $1M around year 13–14. So FIRE around age 44. Bump the savings rate to $40K/year and the date moves up to roughly age 41 — three years earned by saving an extra $10K annually. The outsized impact of the savings rate is what makes FIRE math counterintuitive on first read.

The 4% rule itself comes from the Trinity Study, which back-tested historical U.S. market returns and asked: starting with $X in retirement, withdrawing 4% the first year and adjusting for inflation each year afterward, what's the probability the portfolio outlasts you? For 30-year horizons, the answer was roughly 95% across most starting periods. For early retirees with 50+ year horizons, the safe withdrawal rate is closer to 3.25–3.5% — which means the FIRE number is more like 28–30× expenses, not 25×.

A few honest gaps in the projection: the calculator doesn't model sequence-of-returns risk (a bad market in the first 5 years of retirement is much more damaging than the same market 20 years in, even if average returns over the full retirement match the assumption). It doesn't model healthcare cost growth, which has historically run 5–7% annually — well above general inflation. And it doesn't model lifestyle inflation, which is what most aspiring early retirees underestimate. Treat the projected date as the optimistic case and build a buffer for the things the model can't see.