The same plan at other withdrawal rates
The withdrawal rate is an assumption, not a fact. Lower rates are commonly used for retirements longer than the 30 years the 4% research tested.
| Rate | Multiple | FIRE number | Reached |
|---|---|---|---|
| 3.00% | 33.3× | 1,000,000 | age 59 |
| 3.50% | 28.6× | 857,143 | age 56 |
| 4.00%selected | 25.0× | 750,000 | age 54 |
| 4.50% | 22.2× | 666,667 | age 52 |
What this does not model. The return is applied at a steady rate every month, so there are no good or bad decades and no sequence of returns risk — which is the largest single risk in the years around retirement. It also assumes contributions and spending hold steady throughout, and excludes tax, fees, and any state pension. This is a calculation, not a recommendation.
How the math works
The target is your annual spending multiplied by the inverse of your withdrawal rate. Everything then reduces to a month-by-month projection until the portfolio reaches it.
FIRE Number = Monthly spending × 12 × (100 ÷ withdrawal rate) 4.00% → 25× 3.50% → 28.6× 3.33% → 30× 3.00% → 33.3× Each month: value = value × (1 + r/12) + contribution until value ≥ FIRE Number
Both the return and the spending figure are in today’s money — the return is entered after inflation, so no separate inflation adjustment is applied. Mixing a nominal return with today’s spending is the most common error in this calculation; our guide to return assumptions covers why the two bases cannot be combined.
The withdrawal rate deserves more attention than it usually gets: it is the assumption that moves the target most, and moving from 4% to 3.33% raises the required portfolio by a fifth. Where the 4% figure came from and what retiring at 40, 45, or 50 implies both work through the trade-off.
The Early Retirement Scenario in the Wealth Path app runs this against your real liquid assets rather than a single portfolio figure, and the Coast FIRE calculator finds the earlier milestone where you can stop contributing entirely.
Frequently Asked Questions
What is a FIRE number?
It is the portfolio size at which investment returns can cover your living costs indefinitely. It is calculated as annual spending multiplied by 100 divided by your chosen withdrawal rate — at 4% that is 25 times annual spending, and at 3.33% it is 30 times.
Why does the calculator ask for a return after inflation?
Because spending is entered in today’s money. Keeping both on the same basis means no inflation adjustment is needed anywhere, and the resulting figure is in today’s purchasing power. Entering a nominal return alongside today’s spending is the most common error in this calculation and makes the result look substantially better than it is.
Which withdrawal rate should I use?
The 4% figure comes from research tested against a 30-year retirement. Rates between 3% and 3.5% are commonly discussed for longer retirements, since sustainable rates fall as the horizon extends. The table in the calculator shows the same plan at four rates so the effect of the assumption is visible rather than hidden.
Does it account for a state pension?
No. It assumes the portfolio covers all spending indefinitely, which is the conservative case. A pension starting later reduces what the portfolio has to carry from that point, so the true requirement is generally lower than the figure shown.
What are the main things it leaves out?
The return is applied at a steady rate every month, so there are no good or bad decades and no sequence of returns risk. It also assumes contributions and spending stay constant, and excludes tax, investment fees, and any change in circumstances over what may be several decades.
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The information and calculations provided are for informational and educational purposes only and should not be considered financial, investment, or professional advice. Projections are hypothetical, based on assumptions that may not reflect actual market conditions. Past performance does not guarantee future results, and all investments carry risk of loss. Consult a qualified financial professional before making financial decisions.