Educational information, not individual financial advice.
Key Takeaways
A safe withdrawal rate (SWR) is the percentage of your initial retirement portfolio you can spend each year, adjusted for inflation, without running out of money over a target horizon. The most famous SWR is 4%, based on work by William Bengen in 1994.
Bengen studied historical 30-year periods of U.S. stock and bond returns starting in 1926. He asked: in the worst of those periods, what's the highest starting withdrawal rate you could have taken and still had money at year 30?
The answer: 4% of the initial portfolio, adjusted each year for inflation, survived every historical 30-year period — including ones starting at the peaks before the 1929 and 1966–1982 bear markets.
Example: $1M starting portfolio, 4% = $40,000 first-year spending. Year 2, inflation is 3%, so spending is $41,200. Year 3 inflation is 2%, spending is $42,024. And so on. The portfolio grows or shrinks based on market returns, but spending is driven by inflation, not portfolio value.
The 4% rule is more nuanced than its shorthand suggests:
The 4% rule survived every historical period. It didn't survive easily — the worst starting years (1966 is the canonical example) ended with the portfolio nearly exhausted at year 30. Most periods ended with large surpluses. The rule is calibrated to the worst case, not the average.
Morningstar, Vanguard, and others have updated the analysis using modern data and lower assumed future returns. Current estimates:
The range of "safe" has widened as assumptions vary. Most planners today use 3.5–4% as the starting point, erring lower for conservative clients.
The 4% rule is specifically a 30-year number. For other horizons:
For early retirees (retiring at 50), planning for a 45-year retirement, 3% is often cited as the target. Very conservative retirees aiming to never deplete the portfolio (pass money to heirs) may use 2.5–3%.
It's based on U.S. history. Other countries have seen worse sequences that would have broken the 4% rule. If you believe U.S. exceptionalism will continue, the rule is fine; if you want diversified, global-informed assumptions, use lower.
It ignores dynamic spending. Real retirees don't mechanically inflate spending through a crash. They cut back. Dynamic withdrawal strategies (covered in "Dynamic Withdrawal Strategies") support higher rates because they adjust to conditions.
It ignores guaranteed income. Social Security covers 30–40% of spending for many retirees, dramatically reducing portfolio pressure. Plans with large guaranteed income floors can safely use higher withdrawal rates on the portfolio piece.
It's too rigid. Spending patterns change across retirement — the "go-go / slow-go / no-go" phases. A flat real-terms rule misrepresents both the need and the risk.
A popular dynamic withdrawal approach: start at 5–5.5%, but reduce spending by 10% in any year where the withdrawal rate exceeds the initial rate + 20%. Research supports this approach for sustainably higher starting withdrawals.
The Horizons Retirement Readiness score includes a Withdrawal Rate Safety component that evaluates your projected withdrawal rate against a 3.5–7% range. The Monte Carlo engine runs your plan against hundreds of scenarios to measure survival rate — the fraction of simulations that end with money still in the portfolio at your planning horizon. The Retirement page shows both average and percentile portfolio trajectories.
What does the '4% rule' actually claim?
Known limitations
Sources
Educational information distilled from the Horizons engine methodology — not individual financial advice.
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