BorderFolio/What is FIRE?
What is FIRE? The arithmetic of financial independence
Last reviewed 5 September 2026
FIRE — Financial Independence, Retire Early — is the idea that a portfolio roughly 25 times your annual spending can plausibly fund your life without a paycheck. Everything else about the movement is commentary on that one line of arithmetic: how fast you can get there, what number to aim for, and what the arithmetic quietly assumes. This page states all three plainly, including the parts that change when you don't live in the US.
The definition, without the mythology
Financial independence means your investments can cover your spending indefinitely; retiring early is one thing you can do with that, not a requirement of it. The modern movement traces to Your Money or Your Life (1992) and the early-2010s blogs that turned it into arithmetic, but the mechanism is older than either: spend less than you earn, invest the difference in productive assets, and at some point the assets out-earn your needs.
The two halves separate cleanly in practice. Plenty of people pursue FI without the RE — the point where work is chosen rather than required — and stop there. The math is identical either way.
Your FIRE number
The FIRE number is annual spending divided by a withdrawal rate:
| Withdrawal rate | Multiple of annual spending | FIRE number at $40K/year spending | Usually read as |
|---|---|---|---|
| 3% | 33.3× | $1,333,000 | Conservative — long horizons, non-US markets, early retirees |
| 4% | 25× | $1,000,000 | The convention, from the Trinity study |
| 5% | 20× | $800,000 | Aggressive — assumes flexibility or other income |
| 6% | 16.7× | $667,000 | Optimistic — a stretch under most historical evidence |
Notice what drives the number: spending, not income. A person spending $30K a year with a $60K salary is closer to FI than a person spending $150K on $300K. Spending counts twice — every dollar not spent both shrinks the target and grows the portfolio.
Where the 4% comes from
The 4% rule is shorthand for the 1998 Trinity study, which replayed historical US stock and bond returns through every rolling 30-year retirement window and asked which starting withdrawal rate, adjusted for inflation each year, never exhausted the portfolio. Four percent survived nearly every window for stock-heavy portfolios; that empirical result hardened into a rule of thumb.
Read the fine print before leaning on it: the evidence is US market history over 30-year horizons, gross of the taxes and fees a real investor pays, and it assumes you mechanically withdraw in bad years rather than adjusting. A 45-year early retirement, a non-US market, or a heavy dividend-tax drag each argue for a lower rate — which is why serious FIRE planning treats 4% as one scenario among several, not a promise.
The variants: Lean, Fat, Coast, Barista
| Variant | The idea | What it changes in the math |
|---|---|---|
| Lean FIRE | Retire on deliberately low spending | Small annual spending → small target, but no slack for surprises |
| Fat FIRE | Retire without cutting lifestyle | Large spending → a target several times the lean one |
| Coast FIRE | Front-load contributions, then stop adding and let compounding finish the job by traditional retirement age | Target reached by growth alone; contributions drop to zero after the coast point |
| Barista FIRE | Part-time work covers part of spending; the portfolio covers the rest | Portfolio only needs to fund the uncovered share of spending |
They are all the same equation with different inputs. Which is the useful observation: your FIRE plan is fully described by three numbers — what you spend, what you contribute, and what rate you consider safe to withdraw.
How long it takes: the savings-rate table
The time to FI depends almost entirely on your savings rate — the share of take-home income you invest. With a 5% real return and a 4% withdrawal target, the classic figures run roughly:
| Savings rate | Years to FI (from zero) |
|---|---|
| 10% | ~51 |
| 25% | ~32 |
| 50% | ~17 |
| 65% | ~10.5 |
| 75% | ~7 |
The table assumes the return and the rate hold, which real markets do not promise — treat it as an illustration of the lever, not a schedule. The lever itself is real: moving the savings rate matters far more than picking better funds, because it works on both sides of the equation at once.
What the arithmetic assumes — and where it breaks
- It ignores taxes. The Trinity numbers are pre-tax. Dividends and realized gains are taxed on the way through, and for an international investor a slice of every US-sourced dividend is withheld at source before any home tax applies. Income you cannot spend does not fund a retirement. How the two tax layers stack.
- It is calibrated to US history. Rolling-period studies on other national markets frequently support lower safe rates. A globally diversified portfolio sits somewhere in between.
- Sequence of returns. Two retirements with identical average returns can end differently depending on whether the bad years come first. This is the strongest argument for the conservative end of the rate table, and for flexibility in spending.
- Inflation is someone's inflation. The rule adjusts withdrawals by inflation — but whose? A person earning in euros, holding dollar-quoted funds and spending in a third currency has three inflation rates and an exchange rate between them.
- Thirty years is not fifty. Retiring at 35 stretches the horizon well past what the original evidence tested.
None of this is a reason to discard the framework. It is a reason to track the inputs honestly — actual spending, actual contribution pace, actual after-tax income — rather than assuming the textbook case.
FIRE when you don't live in the US
Most FIRE writing assumes a US investor with US tax wrappers, US funds and dollar spending. Drop any of those assumptions and three things change:
- Dividend income shrinks before it reaches you. Withholding at source depends on where your funds are domiciled and where you are tax resident; a US-domiciled ETF and its Irish UCITS twin deliver different after-tax income for the same holdings. Over a retirement funded from that income, the gap compounds. US ETFs vs Irish UCITS.
- There is no 401(k) to hide in. Tax-advantaged space is smaller or absent in many countries, so the ordinary tax drag on a taxable portfolio matters more, and measuring it matters more.
- Currency sits inside every number. Your FIRE number is denominated in what you spend; your portfolio may be quoted in something else. A plan that ignores the exchange rate is a plan with a hidden variable.
The practical consequence: an international FIRE plan needs its inputs measured on real numbers — contributions at the rate on the day they were made, dividend income after both tax layers, progress in the currency you will actually spend. That measuring is what BorderFolio tracks for FIRE.
Common questions
What is FIRE?
FIRE stands for Financial Independence, Retire Early. The core idea: save a high share of your income into investments until the portfolio is large enough that a sustainable withdrawal — conventionally 4% of its value per year — covers your annual spending. At that point paid work becomes optional. The 'RE' part is optional too; many people pursue only the FI half.
What is a FIRE number?
Your FIRE number is annual spending divided by a withdrawal rate. At the conventional 4% that is 25 times annual spending: someone spending $40,000 a year has a FIRE number of $1,000,000. A more conservative 3% rate implies about 33 times spending; 5% implies 20 times.
What is the 4% rule and where does it come from?
The 4% rule comes from the 1998 Trinity study, which tested historical US stock and bond portfolios over rolling 30-year retirements. Withdrawing 4% of the starting balance in year one, then adjusting that amount for inflation, survived almost every historical 30-year period. It is a planning heuristic derived from US market history — not a guarantee, and not tested on longer horizons, other markets, or after the taxes and fees an international investor actually pays.
Does the 4% rule work outside the US?
The historical evidence behind it is US-market evidence, and studies on other national markets often support lower safe rates. An international investor also loses part of the dividend income to cross-border withholding and home taxation before it can be spent, and may earn in one currency while spending in another. None of that invalidates the FIRE arithmetic — it means the withdrawal rate deserves to be chosen more conservatively and the tax drag measured rather than ignored.