The 4-Percent Rule Was Never Failproof

This paper takes a critical look at the 4-percent withdrawal rule, tracing flaws in the historical data behind it and presenting new evidence that 4-percent withdrawals could not have been sustained by real investors, even within William Bengen's original period. It examines the conditions under which any fixed withdrawal rate succeeds or fails and finds that shifting to more conservative allocations offers little protection when conditions turn adverse.

KEY TAKEAWAYS

• Bengen's original data contained material flaws— transaction costs and mutual fund expenses were excluded, which caused the historical failure rate of 4-percent withdrawals to be understated.
• Fixed withdrawal rates are fragile by design. The conditions under which a given rate can be sustained are narrow; when inflation, sequence of returns, and expense drag interact unfavorably, even conservative allocations cannot prevent portfolio depletion.
• More conservative asset allocations are not a reliable hedge. Shifting a portfolio away from equities offers limited protection against specific failure conditions.
• Flexibility is the real safeguard. Planners who build withdrawal strategies around adaptive spending—rather than a fixed rate—give clients a mechanism that fixed-rate approaches structurally cannot provide.