Is the 4% Rule Still Safe? What Current Research Says About Withdrawal Rates

What Was the Original 4% Rule?

William Bengen's 1994 study analyzed every 30-year retirement period from 1926-1993. The worst starting year (1966 — high inflation, poor stock returns) supported a 4.15% initial withdrawal rate with annual inflation adjustments. The 'SAFEMAX' — the maximum safe withdrawal rate across all historical periods.

The 'Trinity Study' (1998) expanded this with Monte Carlo methods, finding similar results: a 4% initial withdrawal with annual CPI adjustment had about a 95% success rate over 30 years with a 50/50 portfolio.

These studies assumed: 30-year retirement, US-only stocks and bonds, a fixed portfolio, no Social Security or pension, and constant inflation-adjusted spending. When ANY of these assumptions don't match your situation, the 4% number needs adjustment.

Why Has the Number Moved Lower?

Current bond yields are lower than historical averages. The expected real return on a 50/50 portfolio is lower than the historical average used in Bengen's data. Morningstar and other research firms have updated the 'safe' rate to 3.3-3.8% depending on assumptions.

But this misses the bigger picture: the fixed percentage approach is a floor, not a ceiling. Most retirees can spend MORE than 4% because: - They have Social Security (reduces portfolio dependence) - They can adjust spending (not locked into inflation-adjusted constant amounts) - Spending naturally declines in real terms (see our spending decline article) - They may work part-time in early years

The Monte Carlo approach captures all of these — which is why the analysis produces a personalized safe spending range rather than a single number.

What Dynamic Strategies Outperform the Fixed Rule?

1. Guardrails (Guyton-Klinger): Set spending between an upper and lower bound. Increase spending when portfolio grows, decrease when it shrinks. Historically allows initial rates of 5-5.5%.

2. Percentage of portfolio: Withdraw a fixed percentage of current value each year (e.g., 4% of whatever the balance is). Income varies but the portfolio never runs out by construction.

3. Floor-and-ceiling: Guaranteed floor from SS/pension covers essentials. Portfolio provides discretionary spending — which can flex with markets.

The analysis engine's spending sensitivity table shows your success rate across a range of spending levels — essentially giving you a personalized guardrails range.

Want Your Personalized Safe Spending Rate?

The analysis at myaifinancialplan.com calculates your specific safe spending range based on 10,000 Monte Carlo scenarios, your income sources, and your asset allocation. Not a generic 4% — YOUR number. Start free at myaifinancialplan.com.