What it says
Withdraw 4% of your portfolio in your first retirement year, then adjust that dollar amount for inflation annually — and based on historical US market data, a diversified portfolio has typically survived at least 30 years. $1,000,000 saved → $40,000 in year one, inflation-raised thereafter. Flip it around and you get the planning shortcut: annual spending × 25 = the nest egg you need.
Where it came from
The rule traces to 1990s research — financial planner William Bengen's historical withdrawal study and the later "Trinity Study" — which tested withdrawal rates against every historical retirement start year in US data, including retirements that began right before crashes and inflation spirals. Four percent was the rate that survived the WORST historical sequences, not the average one. That's the rule's real meaning: a historically-informed worst-case guideline, not a prediction.
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Where it bends
Sequence risk: two retirees with identical average returns can end wildly differently if one hits a bear market in the first years of withdrawals — early losses plus withdrawals compound against you. Longer retirements: 30 years was the test; early retirees planning 40–50 years often study lower rates. Today vs history: the rule assumes future markets rhyme with the American past — a debated assumption. Rigid inflation raises: real retirees adjust spending in bad years, which meaningfully improves survival odds versus the rule's mechanical raises.
How to actually use it
As a compass, not an autopilot. Use ×25 to size your target (Retirement Savings Calculator builds the path to it), then stress-test your actual plan year by year with the Retirement Withdrawal Calculator — vary the return, inflation, and spending assumptions and watch when the money runs out. If a plan only works at optimistic settings, it isn't a plan yet. David Swensen — architect of Yale's endowment model — spent a career on exactly this problem of sustainable spending from a portfolio (David Swensen profile); the institutional version of this question funds universities forever.
FAQ
Is 4% still safe?
It remains the standard reference point; some researchers argue for lower initial rates in expensive markets, others show flexible spending restores the math. Test ranges, not points.
Does it include taxes?
No — withdrawals from traditional accounts are taxable income; your spending target should be gross of taxes.
What about Social Security?
Outside income reduces what the portfolio must produce — subtract expected benefits from spending before multiplying by 25.
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