Safe Withdrawal Rate Research Reference
Direct answer: The original "4% rule" from the 1994 Bengen study found a 4% initial withdrawal rate (adjusted for inflation annually) succeeded over all 30-year periods from 1926 to 1994 for a 50/50 stock/bond portfolio. Subsequent research and lower bond yields have led many planners to suggest 3.3-3.7% for new retirees.
Key Safe Withdrawal Rate Research Findings
| Study | Year | Portfolio | Time Horizon | SWR Found | Notes |
|---|---|---|---|---|---|
| Bengen (original) | 1994 | 50% stocks / 50% bonds | 30 years | 4.0% | SAFEMAX from 1926-1994 data |
| Trinity Study | 1998 | 50/50 to 75/25 | 15-30 years | 4.0-4.5% | 95% success on 30-yr periods |
| Bengen (updated) | 2006 | 60/30/10 (add small-cap) | 30 years | 4.5% | Small-cap tilt increases SWR |
| Pfau (low-yield env.) | 2012 | 60/40 | 30 years | 3.3-3.7% | Post-2008 low rate environment |
| Kitces (floor) | 2012 | 60/40 | 30 years | 4.5%+ | Rising equity glide path thesis |
| ERN Research | 2018 | 60/40 | 30-60 years | 3.25-3.5% | Early retirees need lower rates |
| Morningstar (2021) | 2021 | 60/40 | 30 years | 3.3% | Low starting bond yields |
| Morningstar (2024) | 2024 | 60/40 | 30 years | 3.7-3.8% | Higher starting bond yields |
Source: Published academic and practitioner research papers cited in References below. Last verified: September 2026.
Frequently Asked Questions
What is the 4% safe withdrawal rule?
The 4% rule states that a retiree can withdraw 4% of their initial portfolio in year one, then increase that dollar amount by inflation each year, with very high probability of not running out of money over 30 years. It was derived from William Bengen's 1994 analysis of U.S. historical returns from 1926 to 1994.
Is the 4% rule still valid?
Debate continues. At today's higher stock valuations and historically low real bond yields (before 2022), many researchers recommended 3.3-3.5%. After 2022's bond yield normalization, Morningstar's 2024 estimate was 3.7-3.8%. The 4% figure remains a reasonable starting point for planning but should be stress-tested against current conditions.
How long should my retirement planning horizon be?
Plan for at least 30 years, and for couples or early retirees, 40+ years. The probability that one member of a 65-year-old couple lives to age 90 is over 50%. Early retirees (retiring at 55) should model 40-50 year horizons, which substantially lowers safe withdrawal rates.