Safe Withdrawal Rates

The 4% Rule

In 1994, financial planner William Bengen asked a simple question: how much can a retiree withdraw from a diversified portfolio each year without running out of money over a 30-year retirement? He tested every rolling 30-year period in the historical U.S. market data going back to 1926 and found that a 4% initial withdrawal rate, adjusted for inflation each year, survived them all — even periods that included the Great Depression and the 1970s stagflation.

The Trinity Study

A few years later, three professors at Trinity University — Philip Cooley, Carl Hubbard, and Daniel Walz — published a study that confirmed and expanded on Bengen's findings. Using rolling 30-year periods from 1926 to 1995, they tested various withdrawal rates across different stock/bond allocations, from 100% stocks to 100% bonds.

Their key finding: a 4% withdrawal rate with a 50/50 to 75/25 stock/bond allocation had a success rate of roughly 95% over 30-year periods. Higher stock allocations slightly improved success rates over long horizons because equities provide the growth needed to outpace inflation and withdrawals.

Why 4% Means 25 Times Your Expenses

The 4% rule has a simple mathematical twin: the 25x rule. If you withdraw 4% of your portfolio each year, that means your portfolio is 25 times your annual withdrawal (because 1 ÷ 0.04 = 25). So if you spend $40,000 per year, you need $1,000,000. If you spend $60,000, you need $1,500,000. If you spend $100,000, you need $2,500,000.

Sequence of Returns Risk

The biggest threat to a 4% withdrawal strategy isn't low average returns — it's bad returns in the first few years. When you're selling shares to fund withdrawals during a market downturn, those shares can't participate in the eventual recovery. Two retirees with identical average returns over 30 years can have completely different outcomes depending on whether the bad years came first or last.

This risk — called sequence of returns risk — is significant enough that we cover it in depth in the dedicated article on sequence risk, including mitigation strategies like the bond tent, guardrails, and bucket approaches. For now, the key takeaway: the first 5–10 years of retirement are the most vulnerable period for your portfolio.

Flexible Withdrawal Strategies

The original 4% rule is rigid — you withdraw the same inflation-adjusted amount regardless of market conditions. Several researchers have proposed flexible alternatives:

• Guardrails approach: Set upper and lower boundaries around your withdrawal rate. If the market drops and your withdrawal rate rises above the ceiling (say 5.5%), you cut spending by a fixed percentage. If the market surges and your rate falls below the floor (say 3.5%), you give yourself a raise. This adapts to market conditions while preventing extremes.
• Percentage-of-portfolio: Withdraw a fixed percentage of the current portfolio value each year (e.g., always 4% of whatever the portfolio is worth). Income fluctuates with the market, but you can never run out of money — the withdrawals shrink as the portfolio shrinks.
• Floor-and-ceiling: A hybrid — withdraw a percentage of the portfolio, but set a dollar floor (minimum withdrawal) and ceiling (maximum withdrawal). This provides stability without the rigidity of a fixed amount.

No single method is "best." Each trades off between income stability (knowing how much you can spend) and portfolio safety (not running out). People who can tolerate some income variability can safely withdraw more on average.

Adjusting for Longer Retirements

The 4% rule was tested against 30-year retirements. If you're retiring at 65 and planning to age 95, 30 years works. But if you're pursuing FIRE and leaving work at 40, you need your money to last 50-60 years. A 4% withdrawal rate starts to look risky over that horizon.

Many early retirees use a 3.25% to 3.5% withdrawal rate, which translates to saving 29-31 times annual expenses instead of 25 times. It's a larger target, but the extra margin provides significantly more safety over a multi-decade retirement.

Another factor: early retirees have more flexibility. At 40, you can return to part-time work, freelance, or reduce spending if the market tanks in your first few years. That flexibility is itself a form of insurance that a 65-year-old retiree may not have.

Spending Isn't Constant

Retirement spending rarely follows a straight line. Researchers have identified three phases:

1. Go-go years (early retirement): Travel, hobbies, dining out, projects you delayed while working. Spending is highest.
2. Slow-go years (mid-retirement): Activity and spending naturally decrease. Many retirees spend 10-20% less than in their early retirement years.
3. No-go years (late retirement): Social activity declines further, but healthcare and long-term care costs can spike. Spending may increase again, but the composition changes dramatically.

This U-shaped spending pattern means a constant withdrawal rate may be too conservative in the slow-go years and not enough in the no-go years if healthcare costs are high. Planning for variable spending — not a fixed annual number — produces more realistic projections.

What These Studies Assumed

Both Bengen's study and the Trinity Study used U.S. stock and bond market data from 1926 onward. The U.S. market had one of the best-performing track records of any country in the 20th century. Not every country was so lucky — investors in Japan, for example, experienced a multi-decade stock market decline starting in 1989.

Future returns may differ from historical returns. Interest rates, valuations, global economic conditions, and demographic trends all affect long-term market performance. Current research suggests safe withdrawal rates might be closer to 3.3-3.5% given today's starting valuations, though the data is debated.

The takeaway: use the 4% rule as a planning framework, not a fixed law. Build in flexibility, have backup plans, and revisit your withdrawal rate as circumstances change.