What FIRE actually means
FIRE — Financial Independence, Retire Early — is the idea that once your invested portfolio is large enough, withdrawals from it can cover your living costs forever, and work becomes optional. The movement's whole engineering problem reduces to two numbers: how much you spend each year, and what fraction of a portfolio you can safely withdraw each year. Divide one by the other and you get the target:
= $36,000 ÷ 0.04 = $900,000 (the classic "25× spending")
Income never appears in that formula. A surgeon spending $150,000 a year needs a far bigger portfolio than a teacher spending $30,000 — which is why the FIRE community obsesses over spending, not salary.
To find when you get there, the calculator doesn't use a closed-form shortcut. It steps year by year: your current portfolio grows at the real return you entered, then a year of savings (income − spending) is added, and it repeats until the balance crosses the FIRE number:
stop when: portfolio ≥ FIRE number → that year's age is your FIRE age
Coast FIRE is the same math run backwards — the amount which, left alone with zero further saving, compounds to your FIRE number by age 65:
The 4% rule and the Trinity study
The default 4% withdrawal rate isn't arbitrary. In 1994, financial planner William Bengen back-tested every rolling 30-year retirement in US market history since 1926 and found that an initial 4% withdrawal, raised with inflation each year, never exhausted a 50–75% stock portfolio — the worst-case survivor he called "SAFEMAX". In 1998, three professors at Trinity University published the study the rule is now named after: across 1926–1995, a 4% inflation-adjusted withdrawal from a 50/50 stock–bond portfolio succeeded in 95% of all 30-year periods. Push the rate to 5% and the success rate drops sharply; at 6% it falls below half. That cliff is why 4% became the community's anchor — it sat right at the edge of "always survived".
Why the safe withdrawal rate is debated
Stocks have returned roughly 7% a year after inflation over the last century, so why can you only withdraw 4%? Because you don't earn the average — you earn a specific sequence. A crash in the first few years of retirement, while you're also withdrawing, permanently shrinks the portfolio before it can recover; the same crash in year 25 barely matters. This is sequence-of-returns risk, and it is the single biggest reason a safe rate sits so far below the average return.
The debate cuts both ways:
- More conservative: the Trinity numbers cover 30 years, but someone retiring at 40 may need 50+. The exhaustive simulations in the Early Retirement Now safe withdrawal rate series suggest roughly 3.25–3.5% is the more defensible starting point for very long horizons, especially when starting at high market valuations.
- More aggressive: Bengen himself revised upward. His 2025 book A Richer Retirement argues that with a more diversified portfolio the historical worst-case rate for 30 years is 4.7%, not 4% — and he has noted the average historical retiree could have taken far more, with inflation, not market crashes, as the withdrawal rate's greatest enemy.
That's why the SWR field here is editable. At $36,000 of spending, moving from 4% to 3.5% raises the target from $900,000 to about $1.03M; Bengen's 4.7% lowers it to about $766,000. Reasonable people land in different places — the calculator just does the arithmetic honestly for whichever rate you pick.
Savings rate is the master lever
The counterintuitive core of FIRE math: your savings rate — the share of take-home pay you keep — controls the timeline almost by itself, because it works both ends at once. Save more and you accumulate faster and you've proven you live on less, which shrinks the portfolio you need. The famous table, popularized by Mr. Money Mustache's "shockingly simple math behind early retirement" (assumes a 5% real return, a 4% withdrawal rate, and starting from zero):
| Savings rate | Working years until FIRE |
|---|---|
| 5% | 66 |
| 10% | 51 |
| 20% | 37 |
| 30% | 28 |
| 40% | 22 |
| 50% | 17 |
| 60% | 12.5 |
| 70% | 8.5 |
| 80% | 5.5 |
Notice the shape: going from 10% to 20% buys you fourteen years; going from 60% to 70% buys four. Every extra dollar saved is a double win, which is why a raise that goes entirely to savings moves your FIRE age far more than a slightly better investment return ever will.
Real vs nominal returns — why the default is 5%
This calculator works entirely in today's dollars. Your spending is today's spending, your FIRE number is today's purchasing power — so the growth rate must be a real (inflation-adjusted) return, not the headline number. US stocks have averaged around 10% nominal, but with ~3% inflation that's roughly 7% real, and a portfolio with bonds in it lands lower. The 5% default is a middle-of-the-road real return for a diversified portfolio; pessimists use 4%, optimists 6–7%. The payoff of working in real terms: when the calculator says "$900,000 at age 50", that's $900,000 of today's purchasing power, and the retirement spending it supports is directly comparable to your current budget. Enter a nominal return and everything will look several years rosier than it should.
Worked example 1 — the 40% saver
Age 30, $50,000 invested, take-home income $60,000, spending $36,000 (so saving $24,000 a year — a 40% savings rate), 5% real return, 4% SWR, same spending in retirement.
- FIRE number: $36,000 ÷ 0.04 = $900,000.
- Timeline: the year-by-year loop crosses $900k in year 20 — after 19 years the portfolio is about $859,000, and one more year of growth and saving pushes it to roughly $926,000. FIRE age ≈ 50. (The from-zero table says 22 years at 40%; the $50k head start shaves about two off.)
- Coast FIRE: $900,000 ÷ 1.0535 ≈ $163,000. With that banked at 30, compounding alone reaches $900k by 65 — every dollar saved beyond it is buying earlier freedom, not basic security.
Worked example 2 — later start, lower SWR
Age 40, $200,000 invested, income $90,000, spending $54,000 (saving $36,000 — again 40%), 5% real, but planning a leaner $48,000 retirement and a cautious 3.5% SWR.
- FIRE number: $48,000 ÷ 0.035 ≈ $1,371,000.
- Timeline: the loop crosses in year 17 (≈$1.39M) → FIRE age ≈ 57.
- SWR sensitivity: at 4% the target falls to $1.2M, which is reached a year earlier, at 56. The stricter withdrawal rate costs one extra working year here — a concrete way to price the safety margin.
Lean, Coast and Fat FIRE
The community's variants are just the same formula pointed at different spending levels, and the calculator shows all three:
- Lean FIRE — independence on a deliberately minimal budget. As an example the calculator prices 25× a budget trimmed 30% below your planned retirement spending; lean-FIRE folk often target total spending under roughly $40k/household.
- Coast FIRE — not enough to quit, but enough that compounding alone finishes the job by 65. Reaching it means you could downshift to work that merely covers the bills.
- Fat FIRE — independence with room to spare; the calculator prices 25× double your planned retirement spending as an illustration.
This page is a mathematical projection with constant returns and no taxes, market crashes or life changes — general information, not financial advice. Talk to a licensed adviser about your own plan.
FAQ
What is a FIRE number?
Your FIRE number is the portfolio size at which investment withdrawals can cover your annual spending indefinitely. The standard formula is annual retirement spending divided by your safe withdrawal rate — at the classic 4% rate that works out to 25 times annual spending. Someone spending $40,000 a year needs about $1,000,000; someone spending $60,000 needs about $1,500,000. Notice it depends only on spending, not on income.
Is the 4% rule safe for a retirement longer than 30 years?
The 4% rule was tested on 30-year retirements, and an early retiree may need the money to last 50 or 60 years. Research at Early Retirement Now covering those longer horizons points to roughly 3.25–3.5% as a more defensible starting point, while Bill Bengen's 2025 update argues 4.7% held historically for 30-year spans with a more diversified portfolio. In practice, flexibility — trimming spending in bad years or earning a little income — matters more than the second decimal of your withdrawal rate.
What is Coast FIRE?
Coast FIRE is the point where your existing investments, left alone with no further contributions, would grow to your full FIRE number by traditional retirement age (65 in this calculator). Once you pass it, you only need to earn enough to cover current living costs — compounding has already solved the retirement problem. The calculator computes it by discounting your FIRE number back from age 65 at your expected real return.
Should I enter real or nominal returns?
Real (inflation-adjusted). This calculator keeps everything in today's dollars — your spending, your FIRE number and the projection — so the return you enter must also be after inflation. An 8–10% nominal stock return minus 2.5–3% inflation is roughly a 5–7% real return; the 5% default is a reasonably conservative figure for a diversified portfolio. If you enter a nominal return, the projected FIRE age will be optimistic.
Does this calculator include Social Security or a pension?
No — it assumes your portfolio covers all retirement spending. If you expect Social Security, a pension or rental income, subtract that reliable annual amount from your retirement spending before it goes into the formula: every $1,000 of dependable yearly income cuts your FIRE number by about $25,000 at a 4% withdrawal rate. Early retirees should be conservative here, since benefits may be decades away and smaller than projected.
What savings rate do I need to retire in 10 years?
Starting from zero, roughly 65–70%. With a 5% real return and a 4% withdrawal rate, a 65% savings rate reaches financial independence in about 10.5 years and 70% in about 8.5 years, because a high savings rate speeds up saving and shrinks the spending your portfolio must support at the same time. Existing savings shorten the wait further — the calculator's year-by-year projection starts from your current portfolio.