The 4% Rule

In 1994, financial planner William Bengen asked a question that changed retirement planning forever: how much can you safely withdraw from a portfolio each year without running out of money over a 30-year retirement? He tested every 30-year period going back to 1926, using a portfolio of 50% stocks and 50% bonds. The answer: 4%. An initial withdrawal of 4% of your portfolio, increased by inflation each year, survived every historical period — including those that included the Great Depression, World War II, the 1970s stagflation, and the 2000 dot-com crash. The 4% rule isn't a guarantee about the future, but it's the most rigorously backtested retirement guideline we have.

How the 4% Rule Works

The 4% rule is simple to apply. In your first year of retirement, withdraw 4% of your total portfolio. If you have $1 million, you withdraw $40,000. In each subsequent year, you adjust that amount for inflation — not for your portfolio's actual performance. If inflation is 3%, your second-year withdrawal is $41,200, regardless of whether the market went up or down.

This inflation-adjusted approach means your purchasing power stays constant throughout retirement. You're not eating less every year because inflation erodes your dollar. You're withdrawing more dollars each year, but they buy the same amount of stuff.

The math works because a balanced portfolio's long-term returns exceed 4%. The S&P 500 has returned roughly 10% per year and bonds about 5%. A 50/50 blend returns roughly 7-8% before inflation, or about 4-5% after inflation. The 4% withdrawal rate stays below this long-term real return, allowing the portfolio to grow (or at least hold its value) over time.

Bengen's later research, and the famous "Trinity Study" by three Texas professors that expanded his work, found that 4% was actually conservative. In the majority of historical periods, a retiree following the 4% rule died with more money than they started with — often two or three times more. The 4% rate is designed to survive the worst case (retiring right before the 1929 crash or the 1966 secular bear market), not the average case.

Why It Matters for Investors

The 4% rule provides two critical pieces of information. First, your retirement number: divide your annual expenses by 0.04 (or multiply by 25) to know how much you need. This makes retirement planning concrete and measurable. Second, a withdrawal framework: once retired, you know how much you can spend each year without fear of depletion.

But the rule has important caveats. It was designed for a 30-year retirement. If you retire at 40 and plan to live to 95, you need 55 years of withdrawals — and 4% may be too aggressive. Most early retirees use 3-3.5% for additional safety margin.

The rule assumes a relatively balanced portfolio (50-75% stocks). A 100% bond portfolio with 4% withdrawals would have failed in several historical periods. You need the growth that stocks provide, which means you need to tolerate the volatility that stocks bring, even in retirement.

The rule doesn't account for Social Security, pensions, or other income sources. If you receive $20,000 per year from Social Security, you only need your portfolio to cover the gap between your expenses and that income. This dramatically reduces the portfolio size needed.

Current critics note that today's bond yields and market valuations differ from historical averages, and some researchers suggest that 3.3-3.5% may be safer for future retirees. Others counter that retirees can adjust spending dynamically — cutting back slightly during market downturns and spending more during booms — which dramatically increases the safe withdrawal rate.

Real Example

A couple retires at 65 with $1.2 million and annual expenses of $48,000 (exactly 4%). Year one, they withdraw $48,000. The market drops 20%, and their portfolio falls to roughly $922,000 (after the withdrawal). They're nervous, but the rule says keep withdrawing — $49,440 in year two (adjusted 3% for inflation). Over the next three years, the market recovers and grows. By year five, their portfolio is at $1.1 million despite having withdrawn nearly $250,000. By year fifteen, they have $1.4 million — more than they started with. The portfolio sustained their lifestyle, survived a crash in the first year, and grew because the long-term returns exceeded the withdrawal rate. This matches the most common historical outcome: the 4% rule doesn't just keep you from running out of money — in most scenarios, it leaves you wealthier than when you started.