Quick answer
Your FIRE number is your annual retirement spending divided by the withdrawal rate you choose, so at 4%, the first-year rate tested in the 30-year studies, it is 25 times your spending: $36,000 a year needs $900,000. In the calculator's own example, someone aged 30 with $50,000 invested and saving $24,000 a year at a 5% real return reaches that number at about age 50.
What FIRE actually means
FIRE — Financial Independence, Retire Early — is the idea that once your invested portfolio is large enough, withdrawals from it can pay your living costs and work becomes optional. The calculation reduces to two numbers: how much you spend each year, and the withdrawal rate, which is the share of the portfolio you plan to withdraw in the first year of retirement. In the studies below that first-year dollar amount is then adjusted for inflation each year; it is not recalculated as a percentage of the portfolio. The literature calls the highest first-year rate that historically lasted a given period the "safe withdrawal rate". Divide spending by the rate and you get the target:
= $36,000 ÷ 0.04 = $900,000 (25× spending at 4%)
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 target is built from 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 comes from studies of US history. In October 1994 financial planner William Bengen (Journal of Financial Planning, reprinted by the Financial Planning Association) used Ibbotson Associates' data to measure how long a portfolio lasted if retirement began in each year from 1926, with a first-year withdrawal adjusted each year for inflation. For a portfolio of 50% stocks and 50% intermediate-term Treasury notes, a first-year 4% was not exhausted before 33 years in any of those retirements, and in most it lasted 50 years or longer; 4.25% could have run out in as little as 28 years. The word "SAFEMAX" is not in the text of the 1994 article: in a December 2020 article Bengen calls it "a term I devised in my own research", the highest first-year withdrawal rate that historically sustained a portfolio for a given period.
In February 1998 Philip Cooley, Carl Hubbard and Daniel Walz, finance professors at Trinity University, published the study known as the Trinity study. It used annual returns for 1926 to 1995, with the S&P 500 for stocks and long-term high-grade corporate bonds for bonds, and counted the share of all past payout periods of 15, 20, 25 and 30 years that a portfolio supported with annual withdrawals; "supported" meant more than $0 left at the end, before taxes and transaction costs. For a 50/50 portfolio paying out for 30 years, with each year's withdrawal adjusted for inflation, that share was 95% of the 41 overlapping periods at a first-year rate of 4%, 76% at 5% and 51% at 6% (Table 3 of the paper). Wade Pfau's re-creation and update of the study, which used intermediate-term government bonds, withdrawals at the start of each year and 60 rolling 30-year periods beginning in 1926 through 1985, found 100% at 4%, 68% at 5% and 43% at 6% for the same 50/50, 30-year, inflation-adjusted case. Different assets and years give different figures, so the two sets are not interchangeable.
Both studies are measurements of past US returns for the portfolios and periods named. The Trinity payout periods ran from 15 to 30 years, and Bengen's charts stop at 50 years.
Why the withdrawal rate is debated, and why the calculator shows three scenarios
Average returns have been higher than the first-year rates the studies found: the S&P 500 compounded at about 6.8% a year after inflation from 1928 to 2025 (worked out under "Real vs nominal returns" below). So why do the studies find a lower first-year rate? Because a portfolio does not earn the average; it earns a particular sequence. Bengen's 1994 article opens with a fictional planner who sets withdrawals from average returns and average inflation, and calls that assumption the logical fallacy that got the planner into trouble; of the three large market declines he lists, 1973 to 1974 was the most damaging because it came with high inflation. Early Retirement Now describes sequence-of-returns risk as follows: a portfolio can run out of money even when its 30-year or 50-year average return was above the withdrawal rate, if returns are poor early and withdrawals continue through the bear market.
The debate cuts both ways:
- More conservative: the Trinity payout periods stop at 30 years, but someone retiring at 40 may need 50 or more. Early Retirement Now simulated 30, 40, 50 and 60-year horizons with monthly returns from 1871; for 60 years it concludes that "3.5% is the new 4%", and its series index says a rate of 3.25% to 3.50% would have survived even the most catastrophic historical market conditions, which it ties to high equity valuations. Its success criterion, which it says is the Trinity study's, was a final asset value of zero.
- More aggressive: Bengen has since put his figure higher. CNBC reported in September 2025 that his 1990s research pointed to a maximum safe first-year rate of 4.15% for a 30-year, 60/40, tax-advantaged portfolio and that, according to his calculations, it is now 4.7%, which he calls "Universal Safemax" and CNBC describes as "the historical maximum safe withdrawal rate for all retirees". The same article says his historical data shows some retirees may be able to withdraw more, with the average Safemax rate at about 7.1%. CNBC does not give the portfolio or horizon behind the 4.7%, says it rests on past performance and is not guaranteed to hold for future retirees, and quotes Bengen calling inflation the "greatest enemy of retirees".
That is why the results show three rates rather than one. The first tile uses this calculator's own steps for how long your money has to last, counted from the FIRE age projected at your own rate to your "planning to age": 4% up to 30 years, 3.75% past 30, 3.5% from 35 and 3.25% from 45. They run from the 4% the 30-year studies tested down to 3.25%, the low end of the 3.25% to 3.5% range in Early Retirement Now's series index. Early Retirement Now's own figure for a 60-year retirement is 3.5%, so the 3.25% step is below it. None of the sources cited here publishes these steps or the horizons where they start. When the projection does not reach the number, or reaches it at or after your planning age, there is no retirement length to count and the tile shows 3.5%. The second tile is the 4% tested in the 30-year studies and the third is the 4.7% Bengen reports, as CNBC describes it. Your own rate is shown alongside whenever it differs. At $36,000 of spending, moving from 4% to 3.5% raises the target from $900,000 to about $1.03M, and 4.7% lowers it to about $766,000. The tiles show the arithmetic at each rate; none of them predicts what a portfolio will do. The chart and the Lean, Coast and Fat variants stay bound to the rate you set.
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. This table is from 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 |
The table starts from $0 — your personalized results above start from your actual current savings, which is why they usually arrive sooner. Notice the shape: going from 10% to 20% buys you fourteen years; going from 60% to 70% buys four. Mr. Money Mustache's point is that cutting spending is more powerful than raising income, because every permanent drop in spending both leaves more to save and permanently lowers what you will need.
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. For scale, by our own calculation from two published tables, the S&P 500 with dividends compounded at about 10.0% a year from 1928 to 2025 (the annual returns in Damodaran's table, NYU Stern, January 2026) while consumer prices rose about 3.0% a year over the same years (the annual averages in the Federal Reserve Bank of Minneapolis CPI table), which is about 6.8% a year after inflation: (1.100 ÷ 1.030) − 1. That is one US index over one period, not a forecast. The 5% default is the real return Mr. Money Mustache's table assumes, so the worked examples line up with it. 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 as if it were real and every result arrives sooner than it should — which is why the return field has a toggle: switch it to "Nominal + inflation", enter the headline figure your brokerage statement quotes plus an inflation assumption, and the calculator converts it properly (real = (1 + nominal) ÷ (1 + inflation) − 1 — division, not subtraction, though at normal rates the two are close) and shows the real rate it actually uses.
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, a 4% withdrawal rate, 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 at 5% real reaches $900k by 65; savings beyond it move the projected FIRE age earlier.
- Horizon check: with the default "planning to age 90", a FIRE age of 50 is a ~40-year retirement, longer than the 30-year payouts tested in the Trinity study, so the calculator's hint offers its own 3.5% step. At 3.5% the target is about $1.03M and the projected FIRE age 52: two more working years in this projection.
Worked example 2 — later start, lower withdrawal rate
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 3.5% withdrawal rate.
- FIRE number: $48,000 ÷ 0.035 ≈ $1,371,000.
- Timeline: the loop crosses in year 17 (≈$1.39M) → FIRE age ≈ 57.
- Withdrawal-rate sensitivity: at 4% the target falls to $1.2M, which is reached a year earlier, at 56. In this projection the lower rate adds one working year.
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 — a deliberately minimal budget. As an example the calculator prices a budget trimmed 30% below your planned retirement spending, at your withdrawal rate (25× at the 4% default).
- Coast FIRE — the portfolio that, with no further contributions, compounds to your FIRE number by 65 at the return you entered.
- Fat FIRE — a larger budget; the calculator prices double your planned retirement spending at your withdrawal rate, 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 whose withdrawals at a chosen rate equal your annual spending: annual retirement spending divided by that rate. At 4%, the first-year rate tested in the 30-year studies, that works out to 25 times annual spending. Someone spending $40,000 a year gets about $1,000,000; someone spending $60,000 gets about $1,500,000. Notice it depends only on spending, not on income. Whether a portfolio of that size would last depends on returns, inflation and how long it has to last; the calculator does not test that, it divides spending by the rate you set.
Is the 4% rule safe for a retirement longer than 30 years?
The 4% figure comes from studies that asked whether a portfolio would last 30 years. In William Bengen's 1994 article, a 50/50 portfolio of stocks and Treasury notes that paid out 4% in the first year, adjusted for inflation afterwards, lasted at least 33 years in every historical retirement he tested. In the 1998 Trinity study, a 50/50 portfolio of stocks and corporate bonds paying 4% with inflation-adjusted withdrawals had money left in 95% of 30-year periods between 1926 and 1995. An early retiree may need the money to last 50 or 60 years. Early Retirement Now simulated horizons of 30 to 60 years and concludes that 3.5% is its figure for 60 years; its series index says 3.25% to 3.50% would have survived even the most catastrophic historical market conditions. CNBC reported in September 2025 that, according to Bengen's calculations, the maximum safe withdrawal rate is now 4.7%. The 1994 and 1998 figures measure past US returns, and none of these sources says what a particular portfolio will do. This calculator's own steps between 4% and 3.25% are not published by any of them.
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) at the return you entered. Past it, the projection no longer needs contributions to reach the number, though you would still need income for living costs until then. 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?
Either — just set the toggle at the return field to match. The calculator keeps everything in today's dollars, so the projection always runs on a real (inflation-adjusted) return. On 'Real (after inflation)', enter the real return you want to test (the default, 5%, is the real return Mr. Money Mustache's table assumes). On 'Nominal + inflation', enter the headline figure a brokerage statement quotes plus your inflation assumption, and the calculator converts it properly — real = (1 + nominal) ÷ (1 + inflation) − 1, shown beneath the field — before projecting. Entering a nominal return while the toggle says real overstates the real return, so every result arrives sooner than it should, which is why real-mode entries above 7% get a warning.
Does this calculator include Social Security or a pension?
Yes, optionally — enter the yearly amount in today's dollars and the age it starts (67 is assumed if you leave the start age blank: the US full retirement age for anyone born in 1960 or later; in Canada the standard age for CPP is 65 and OAS starts at 65 at the earliest). From the pension's start age it reduces the spending your portfolio must cover; before that age you fund the gap yourself. Leaving the amount blank models no pension at all. Benefits that start decades from now may differ from today's projection of them.
How is pension income modelled?
The standard simple way. After the pension starts, your portfolio only needs to cover spending minus pension, so the core FIRE number is max(0, spending − pension) ÷ withdrawal rate. If your projected FIRE age comes before the pension's start age, the calculator adds a bridge fund — the pension amount times the gap years — that you spend down while waiting. If the pension covers all of your retirement spending, your FIRE number is just that bridge. The model ignores taxes, benefit cuts and claiming rules.
What savings rate do I need to retire in 10 years?
Starting from zero, roughly 65–70%. Mr. Money Mustache's table, which assumes a 5% real return and a 4% withdrawal rate, gives 10.5 years at a 65% savings rate and 8.5 years at 70%, 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.