FIRE glossary
Safe Withdrawal Rate (SWR)
The percentage of your investable portfolio you draw each year in retirement — the input that turns a spending target into a required pot size.
Where the 4% rule comes from
The famous "4% rule" traces back to the Trinity Study, which tested fixed withdrawal rates against 1926–1995 US market data across rolling 30-year retirement windows and a roughly 50/50 stock-and-bond portfolio. A 4% initial withdrawal — raised each year afterward in line with inflation — survived almost every one of those historical 30-year stretches without running the portfolio to zero. That's the entire basis for the number: not a law of markets, but a single historical-data result that later research has revisited, narrowed, and in places challenged.
Why Ember treats it as an input, not a constant
Ember's engine deliberately makes the SWR a setting you choose rather than a number baked into the maths. 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 sequence of returns (see sequence-of-returns risk). The honestly conservative range for that longer horizon sits closer to 3.25–3.5%, and different asset mixes, jurisdictions and life expectancies all imply somewhat different numbers again. Set a custom rate and Ember checks it every time a plan is computed — flagging it in the trace when it looks unusually aggressive (above roughly 4.5%) or unusually conservative (below roughly 2.5%), rather than silently accepting either.
From rate to required pot
The formula itself is simple — required pot = annual spend ÷ SWR — but Ember grosses the spend up for income tax first. If some of the withdrawal comes from a taxable account, the engine solves iteratively for the gross withdrawal that nets your target spend after tax, then divides that figure by the SWR. Two people with identical spending targets and the same withdrawal rate can end up with different required pots purely because of which account the money is drawn from and where they're tax-resident.
Choosing your own rate
A lower SWR isn't automatically "more correct" — it trades a larger, harder-to-reach required pot for more headroom against a bad sequence of returns. Ember doesn't pick a rate for you: pair a chosen SWR with a Monte Carlo simulation or a historical backtest to see how it actually performs against real historical sequences, rather than trusting the percentage on its own.
Worked example
Two withdrawal rates against the same $40,000/yr spend
At a 4% SWR (25×)
US$1,000,000
requiredPot = spend ÷ 0.04
At a 3.25% SWR (≈30.8×)
US$1,230,769
the more conservative early-retirement figure
Fixed illustrative inputs, not your data — for the exact maths behind your own numbers, use the free calculator or build a plan. Educational modelling, not financial advice.
Across borders
Because the required pot is grossed up for tax on the taxable share of your withdrawal, moving to a country with little or no income tax can lower your required pot at the same withdrawal rate — and moving the other way raises it. See how income tax is modelled for each country Ember covers on /countries.
Common questions
Is 4% actually safe for an early retirement?
No single number is "safe" for every horizon. The Trinity Study tested 30 years; a 40–50-year early-retirement horizon carries more sequence-of-returns risk, and 3.25–3.5% is the more conservative range early-retirement researchers point to. Ember lets you set a custom SWR and flags it when it drifts outside a reasonable band.
Does the safe withdrawal rate already account for tax?
Yes — Ember grosses up your net spending target by the income tax owed on the taxable share of the withdrawal (based on the assets you'd actually draw from and your tax residency) before dividing by the SWR, so the required pot already reflects tax, not just the rate.
What's the difference between SWR and drawdown-to-zero?
An SWR-basis pot targets a rate that, in the constant-return model, never fully depletes. A drawdown-to-zero pot is sized to run out (or nearly) exactly at your life expectancy — usually a smaller number for the same spend. See the drawdown-to-zero term.
Related terms
See safe withdrawal rate (swr) 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.