FIRE glossary
25× Rule
A shorthand for a 4% safe withdrawal rate, stating the same relationship the other way round: your required portfolio is about 25 times your annual spend, because 1 ÷ 0.04 = 25.
Where 25× comes from
The number is pure arithmetic, not a separate finding: if a 4% withdrawal rate is judged sustainable, then dividing your annual spend by 0.04 is the same as multiplying it by 25. The 4% figure itself traces back to the Trinity Study, which tested fixed withdrawal rates against US market data across rolling 30-year retirement windows. "25× your spend" is simply that result restated as a shortcut people can do in their heads — useful for a rough gut-check, but it inherits every limitation of the 4% figure it's built on.
Why Ember doesn't hardcode 25×
Ember's engine computes your required pot as annual spend ÷ SWR, using whatever withdrawal rate you've set — not a fixed 25× multiple. The engine's own code comment is explicit that the Trinity Study's 30-year horizon doesn't generalise cleanly to a 40–50-year early-retirement horizon, where more years in retirement means more exposure to a bad early run of returns. A rate closer to 3.25–3.5% is the more honestly conservative range for that longer horizon, which works out closer to 28.6–30.8× — noticeably above the popular round number.
A useful shortcut, not a target
25× is a fine way to sanity-check a spend figure in your head, but treating it as the target itself skips the step that actually matters: choosing a withdrawal rate appropriate to your horizon, asset mix and tax residency, then letting the multiple fall out of that choice. Ember also grosses your spend up for income tax on the taxable share of the withdrawal before applying the multiple, so two people with identical spending and the same nominal rate can still land on different required pots.
Across borders
The 25× multiple itself is fixed arithmetic — 1 ÷ 0.04 — and doesn't change by country. What changes is the spend figure Ember applies it to: the engine grosses your net spending target up for income tax on the taxable share of the withdrawal before multiplying, so that grossed-up figure — and the required pot built from it — comes out larger wherever withdrawals are taxed, and stays closer to exactly 25× your net spend in a tax-free jurisdiction. Moving to a lower-tax country shrinks the gross figure the multiple gets applied to, which is where most of the cross-border difference in a "25× number" actually comes from. See /countries for how each jurisdiction's tax is modelled.
Common questions
Is 25× a separate rule from the 4% rule?
No — it's the same rule stated as a multiple instead of a percentage. 1 ÷ SWR = multiple, so a 4% rate is 25×, a 3.5% rate is about 28.6×, and a 3.25% rate is about 30.8×. Pick either framing; the maths underneath is identical.
Does Ember use exactly 25×?
Only if your withdrawal rate is exactly 4%. Ember's default safe-withdrawal-rate basis lets you set any custom rate, and the engine flags it in the trace if it looks unusually aggressive (above roughly 4.5%) or unusually conservative (below roughly 2.5%) rather than assuming 25× is correct for you.
Why do some FIRE calculators use a bigger multiple, like 30×?
Because they've chosen a lower withdrawal rate for a longer horizon. The Trinity Study's 4%/25× result was tested over 30-year retirements; a 40– to 50-year early-retirement horizon carries more sequence-of-returns risk, and 3.25–3.5% (roughly 28.6–30.8×) is the more conservative range early-retirement researchers point to.
Related terms
See 25× rule in your numbers
The free calculator gives a rough estimate; the full planner models your actual accounts, pensions, residency moves and taxes — with the maths behind every figure shown.