The 4% rule gives you a withdrawal rate. The 25× rule gives you the same answer, faster. Multiply your annual spending by 25. That is your FIRE number. Spend $40,000 a year? You need $1,000,000. Spend $100,000? You need $2,500,000.
The two rules are mathematically identical. The 25× rule just inverts the 4% rule, because most people find multiplying by 25 easier than dividing by 0.04. This article is about why that simple flip is more useful than it looks — and where it stops being safe.
The math, one line
The 4% rule says: withdraw 4% of your starting portfolio each year, inflation-adjusted.
Flip the fraction:
1 / 0.04 = 25So if you withdraw 4% per year, you need 25 years of expenses saved up. Your FIRE number is:
FIRE number = annual expenses × 25That is the whole rule. There is no other math. Anything more complicated is a different rule in disguise.
Why multiplication beats division
Humans are bad at division. Hand someone an annual spending number and ask them to divide by 0.04 — most people hesitate, pull out a calculator, second-guess the decimal. Hand them the same number and ask them to multiply by 25, and they often do it in their head, because "times 25" is just "times 100, divided by 4," and most people can do both halves mentally.
This is not a small thing. The whole point of the FIRE movement is to make the math graspable enough that ordinary people can plan their own retirement. Multiplying by 25 fits in a tweet. Dividing by 0.04 does not.
The 25× rule is the 4% rule made memorable. The math is the same. The mental model is sharper because most people can do "times 25" without breaking flow.
There is also a second psychological benefit. Multiplication front-loads the answer. You take your spending, multiply, and immediately see a target dollar amount — a number you can compare to your actual portfolio. Division goes the other way: you take your portfolio, divide, and get a withdrawal rate you then have to interpret. The 25× version points you at the goal. The 4% version points you at the current position. Both are useful, but the first one is what most planners actually need.
Examples at three spending levels
Here is the 25× rule applied to three common FIRE spending levels:
| Annual spending | FIRE number (25×) | Notes |
|---|---|---|
| $30,000 | $750,000 | Lean FIRE territory |
| $40,000 | $1,000,000 | Standard FIRE |
| $60,000 | $1,500,000 | Comfortable FIRE |
| $100,000 | $2,500,000 | Fat FIRE |
Each row is the same math. The numbers scale linearly, which is the rule's biggest strength: if your spending doubles, your FIRE number doubles. There is no compounding, no inflation adjustment, no fudge factor. The 25× rule is a clean linear map from spending to portfolio.
The conservative cousin: 30× and 33×
The 25× rule assumes a 4% withdrawal rate. Some FIRE planners go further.
A 30× rule corresponds to a 3.33% withdrawal rate. A 33× rule corresponds to a 3% withdrawal rate. Both are more conservative variants of the same idea.
Why would you use them?
- You plan to retire early and need the money to last 50+ years, not 30.
- You expect higher inflation or lower future returns than the historical average.
- You want a larger cushion against sequence-of-returns risk.
- You hold a meaningful bond allocation and accept lower expected returns.
The same spending, mapped to each rule:
| Annual spending | 25× (4% SWR) | 30× (3.33% SWR) | 33× (3% SWR) |
|---|---|---|---|
| $40,000 | $1,000,000 | $1,200,000 | $1,320,000 |
| $60,000 | $1,500,000 | $1,800,000 | $1,980,000 |
| $100,000 | $2,500,000 | $3,000,000 | $3,300,000 |
The difference between 25× and 33× is roughly 30% more portfolio for the same lifestyle. That is several extra working years for most people — or several extra years of compounding for someone on the Coast FIRE path. The tradeoff is real, and it is yours to make.
Why 25× is not a guarantee
The 25× rule is a clean restatement of the 4% rule. It inherits everything the 4% rule inherits — including its flaws.
First, it assumes your spending stays flat in real terms. Most people do not actually spend the same dollar amount, adjusted for inflation, for 30 straight years. Spending flexes with life: kids, healthcare, travel bursts, paid-off houses, long-term care. A single FIRE number is a snapshot, not a movie.
Second, it assumes the 4% rule holds. As we covered in the 4% rule explainer, the 4% rule was calibrated to historical worst-case sequences and a 30-year horizon. It was not built for the 50-year retirements that early FIRE planners need. Many planners drop to 3.5% — which corresponds to a 28.5× rule — for exactly this reason.
Third, it ignores sequence risk. Two $1,000,000 portfolios can both average 7% real and end up in completely different places, depending on which years were bad. The 25× rule gives you a target. It does not protect you from a market crash in year one.
Multiplying by 25 gets you a target. Stress-testing that target against bad sequences is what actually pays the bills.
How to use the 25× rule well
The 25× rule is a starting point, not a finish line. A defensible plan does the following:
- Calculate your true annual spending. Use last year's actual numbers, not a guess. Most people underestimate by 10-20%.
- Multiply by 25 to get your baseline FIRE number. This is the number the 4% rule says you need.
- Multiply by 30 or 33 to get your conservative target. Pick the one that lets you sleep at night.
- Stress-test against variable returns. Use the Coast FIRE calculator to model what happens if the market drops 25% in your first year of retirement.
- Build a cash buffer. One to two years of expenses in cash or short-term bonds means you are not forced to sell equities in a drawdown.
The 25× rule is the cleanest summary of the FIRE math. It is the 4% rule flipped upside down — which makes it easier to remember, easier to calculate, and easier to share. The simplicity is its strength.
It is also its weakness. The 25× rule hides everything the 4% rule hides: variable spending, sequence risk, longer horizons, lower future returns. Use it as the floor it is. Do not confuse it with a ceiling.