FIRE — Financial Independence, Retire Early — is a movement built on a deceptively simple idea: if you save and invest an unusually large share of your income, you can accumulate enough wealth to cover your living expenses indefinitely, decades before traditional retirement age. The math behind it isn't exotic — it's the same compound growth and safe withdrawal rate logic used in conventional retirement planning — but FIRE pushes the savings rate variable much harder than most people consider, and that single lever changes the timeline dramatically.

This is the same 4% rule used in traditional retirement planning (see our Retirement Planner for the full background on the Trinity Study this is based on). If you spend $50,000 per year, a portfolio of $1.25 million can theoretically sustain that spending indefinitely, withdrawing 4% in the first year and adjusting for inflation afterward. The entire FIRE movement is essentially built on reaching this number as fast as possible — and the fastest lever for that isn't a higher salary or better investment returns, it's a higher savings rate.

A counterintuitive insight from FIRE math: your savings rate alone — independent of your income level — determines roughly how many years until you reach financial independence, assuming a consistent real investment return. This is because a higher savings rate does two things simultaneously: it adds more to your portfolio each year, and it lowers your annual expenses, which lowers your FI number (since FI number is 25x expenses, not 25x income).

Notice that doubling your savings rate from 25% to 50% doesn't just modestly speed things up — it nearly cuts your timeline in half, from 32 years to 17. This is why FIRE adherents focus so intensely on the savings rate percentage rather than income alone: someone earning $200,000 and saving 10% is on a far longer path than someone earning $60,000 and saving 50%.

*Figures assume roughly $40K-$120K in annual expenses at a 4% withdrawal rate; your own numbers will scale with your actual spending.

Coast FIRE asks a different question than the other variants: "how much do I need right now such that, even if I never save another dollar, compound growth alone carries this amount to my full FI number by the time I want to retire?" Reaching your Coast FIRE number is a meaningful psychological and practical milestone — from that point forward, you could theoretically work purely to cover current living expenses (no more retirement saving required) and still retire on schedule.

Named after the idea of working a part-time job (often one with benefits, like at a coffee shop) to cover a portion of living costs, Barista FIRE meaningfully lowers the portfolio size needed since the part-time income offsets some of the annual withdrawal need. Someone with $60,000 in annual expenses who can comfortably earn $20,000 from part-time work only needs a portfolio covering the remaining $40,000 — a $1,000,000 number instead of $1,500,000.

Because FIRE retirees typically have a much longer post-retirement horizon than a traditional 30-year retirement window — often 40, 50, or more years — they're more exposed to sequence-of-returns risk: a poor run of market returns in the first several years after retiring can do outsized damage, since withdrawals are being taken from a depressed portfolio that has decades left to potentially recover. Many FIRE planners build in a margin of safety — retiring with somewhat more than the bare 25x number, or maintaining some flexibility to earn supplemental income if markets turn down early.

This tool projects your path to FI based on a consistent savings rate, a steady average investment return, and a fixed safe withdrawal rate. It does not model market volatility year to year, changes in income or expenses over time, healthcare cost changes, or one-time windfalls or setbacks. Treat the output as a planning estimate and directional guide, not a guarantee — and revisit the numbers periodically as your actual income, spending, and portfolio evolve.