The 4% rule, explained

Where the rule came from

In 1994 financial adviser William Bengen back-tested every 30-year retirement period in US history since 1926. He wanted to find the highest initial withdrawal rate that never ran out of money — even for someone who retired right before the Great Depression or in the stagflation of the 1970s.

The answer was about 4.15% for a portfolio of 50% stocks / 50% bonds. Round that down to 4% and you have one of the most quoted numbers in personal finance.

How it works in practice

Say you retire with £1,000,000:

• Year 1: withdraw 4% × £1,000,000 = £40,000
• Year 2: withdraw £40,000 × 1.025 (2.5% inflation) = £41,000
• Year 3: withdraw £41,000 × 1.025 = £42,025
• ...and so on, regardless of what the market does

The point is that you give yourself a stable inflation-protected paycheck while your portfolio absorbs market swings.

The flip side: when it can fail

The 4% rule is a strong starting point but it has weaknesses:

• It's based on US data. The 20th century US was the best-performing major market. Other countries had lower safe rates.
• It assumes a 30-year retirement. Retire at 50 and need 40+ years, and the safe rate drops closer to 3.25-3.5%.
• It ignores sequence-of-returns risk in extremes. A bad first decade still hurts even within the rule.
• It's a rigid rule. Most real retirees adjust spending up or down based on portfolio performance.

Modern alternatives

• Dynamic 4% rule — Adjust withdrawals based on portfolio performance (Guyton-Klinger guardrails).
• 3.3% rule — Morningstar's lower starting point for today's market valuations.
• Bucket strategy — Hold 1-3 years of cash separately so you never sell stocks in a crash.

Use it as a planning yardstick

Even with its limitations, the 4% rule is the simplest way to translate a savings number into an income number. Our calculator uses it to estimate your monthly retirement income — try different retirement ages and contributions to see how the income changes.