The 4% Rule: How It Works, Where It Breaks, and What to Use Instead

The 4% Rule means: in year 1 of retirement, withdraw 4% of your portfolio. Each subsequent year, withdraw the same dollar amount plus inflation — not 4% of the new balance. If your $1M portfolio grows to $1.2M in year 3, you still withdraw roughly $40,000 plus cumulative CPI, not $48,000. The rule assumes a diversified portfolio of 50–75% US stocks and the remainder in US intermediate-term bonds, rebalanced annually. Bengen's 1994 paper tested this approach against every rolling 30-year historical period from 1926 through 1992 and found that 4.15% (the 'SAFEMAX') never exhausted a portfolio — even for retirees unlucky enough to retire into the 1966 stagflation or the 1929 crash.

Before Bengen's paper, financial planners commonly recommended withdrawing ~5% of initial portfolio value, adjusted for inflation. Bengen, then a California financial advisor, rigorously backtested this and found it had meaningful failure rates. His paper — dense, statistical, and initially published in an obscure journal — eventually became the most-cited piece of retirement research ever produced. The 1998 Trinity Study (Cooley, Hubbard, Walz) extended the analysis across multiple portfolio allocations, confirming that 4% was safe and 5% was not. In 2020, Bengen revised his own number upward to 4.5–4.8% using a more diversified portfolio including small-cap value, international equities, and T-bills.

The 4% Rule was designed for 30-year retirements. If you retire at 45 and live to 95, you have a 50-year horizon — and the historical data does not support 4% at that duration. Wade Pfau's research shows that safe rates drop to roughly 3.25–3.5% for 50-year retirements. Second, the original research used only US equity and bond data from 1926 onward. Non-US investors, or investors expecting lower future US returns (high CAPE ratio arguments), need more conservative rates. Third, the rule assumes you can tolerate large portfolio drawdowns without panicking and selling — historical success assumes you stay invested through bear markets. Fourth, the rule ignores taxes and fees: every percent of expense ratio directly reduces your effective SWR. Finally, the rule is inflexible. Real retirees adjust spending during downturns (the Guyton-Klinger Guardrails approach), and doing so raises your safe initial rate substantially.

• “Original 4.15% SAFEMAX tested 1926–1992” — Bengen (1994), Journal of Financial Planning
• “95–100% success rate over 30 years for 4% withdrawals” — Cooley, Hubbard, Walz (1998), AAII Journal
• “Revised 4.7% with diversified portfolio” — Bengen interview, FA Magazine 2020
• “Long-horizon adjustment to ~3.25–3.5%” — Pfau, Finke, Blanchett (2013)

• Bengen (1994), 'Determining Withdrawal Rates Using Historical Data', Journal of Financial Planning (accessed 2026-04-17)
• Cooley, Hubbard, Walz (1998), 'Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable', AAII Journal (accessed 2026-04-17)
• Pfau & Kitces (2013), 'Reducing Retirement Risk with a Rising Equity Glidepath', Journal of Financial Planning (accessed 2026-04-17)
• Bogleheads Wiki — Safe Withdrawal Rates (accessed 2026-04-17)

Last verified: 2026-04-17