Your “FIRE number” is the portfolio size that could sustain your spending indefinitely at a chosen withdrawal rate. This works it out from your expenses, and how long it takes to get there at your current savings rate.
How it works
FIRE number
FIRE number = annual expenses ÷ withdrawal rate
At the commonly cited 4% withdrawal rate, this is the same as annual expenses × 25 — the two are the identical relationship (1 ÷ 0.04 = 25).
The 4% rule is a historical estimate, not a law of finance
It traces back to the 1998 “Trinity Study,” which examined historical US market data to find a withdrawal rate with a high historical success rate over a 30-year retirement. It was tested primarily against historical US stock and bond returns over that specific window — a retirement longer than 30 years, a portfolio invested very differently from that dataset, or future returns that don’t resemble the historical record could all produce a different real-world outcome. Some more recent analyses argue for a somewhat lower rate, especially for a longer expected retirement, as a more conservative choice. This calculator’s rate field is adjustable specifically because 4% is a commonly cited starting point, not a number this page insists is correct for every situation.
How to use this calculator
- Enter your expected annual expenses in retirement.
- Set a withdrawal rate — 4% is the common starting point, lower is more conservative.
- Optionally, enter your current savings and monthly contributions to see years until you reach it.
Frequently asked questions
Why 25 times annual expenses specifically?
It’s the mathematical inverse of a 4% withdrawal rate: withdrawing 4% of a portfolio each year is the same relationship as the portfolio being 25 times the annual amount withdrawn.
Is a lower withdrawal rate always safer?
Generally considered more conservative, since it requires a larger portfolio relative to spending and leaves more buffer against poor early returns — but it also means needing to save more before reaching your number, a real trade-off, not simply a strictly better choice.
Does the 4% rule account for taxes?
Not directly — the original study focused on portfolio survival, not the tax treatment of withdrawals, which varies by account type (see the Roth vs. Traditional calculator) and could mean your actual spendable amount is somewhat less than the raw withdrawal figure.
What if my expenses will change significantly in retirement?
Use your best estimate of actual retirement spending, not current spending, if the two are likely to differ — healthcare, travel, or paying off a mortgage before retiring can all shift the number meaningfully in either direction.
Is FIRE realistic for most people?
This calculator computes the arithmetic of the target and the timeline to reach it at a stated savings rate — whether that combination is realistic for a given income and expense level is a personal question this calculator doesn’t judge, only illustrates.
