What is the 4% rule for retirement?

Retirement planning has one math problem that haunts everyone: how much is enough? The 4% rule is the closest thing the industry has to an answer. Save twenty-five times your annual spending, spend 4% a year, and the money should last thirty years.

Short answer: the 4% rule says you can withdraw 4% of your portfolio in your first year of retirement, then adjust that amount for inflation each year after, with roughly a 95% chance the money lasts 30 years. It is a starting point for planning, not a guarantee — and it rests on a stack of assumptions most people never read.

Where the number came from

In 1994, a financial planner named William Bengen published a paper asking a simple question: what withdrawal rate would have survived every 30-year retirement in U.S. history? He ran the numbers on a portfolio of stocks and bonds and landed on 4%. A few years later, a team at Trinity University confirmed the result with their own data, and the "Trinity study" became the academic backbone of the rule.

The rule was never meant to be a law of nature. Bengen was looking backward at American market history — roughly 1926 onward — and asking what would have survived the worst of it: the Great Depression, the stagflation of the 1970s, the dot-com bust. The 4% rate was the worst-case survivor, not the average case. In most historical scenarios, retirees could have withdrawn much more and died rich.

That distinction matters. The rule is deliberately conservative. It is built for the retiree who retires the year before a crash, not the average one.

How it works in practice

The math is simple. If you spend $60,000 a year, you need $1.5 million saved (25 times spending). In year one of retirement, you withdraw $60,000. In year two, if inflation was 3%, you withdraw $61,800. You keep adjusting for inflation every year, regardless of what the market does.

Notice what the rule does not ask you to do: it does not ask you to watch the market, rebalance aggressively, or time anything. It is a mechanical plan. That is its appeal. Most people cannot handle a retirement plan that requires them to make smart decisions during a crash, so a plan that requires no decisions at all has real value.

The 25-times number is just 1 divided by 0.04. Want to spend more conservatively at 3.5%? You need about 28.6 times your spending. Comfortable with 5%? Twenty times. The whole rule is arithmetic wearing a lab coat.

The assumptions hiding inside

Every simple rule hides a stack of assumptions, and this one is no exception.

First, it assumes a 30-year retirement. Retire at 65 and it covers you to 95. Retire at 40, as the early-retirement crowd wants to, and 30 years of runway is not enough — you need 50 or 60 years, and the math gets noticeably worse.

Second, it assumes roughly a 50/50 mix of stocks and bonds, periodically rebalanced. All cash would not have kept up with inflation; all stocks would have survived more often but with gut-wrenching drawdowns.

Third, it assumes U.S. market history, which has been one of the best-performing markets in world history. Retirees in other countries, with other markets, have not always had the same luck. Japan's retirees in the 1990s would tell a different story.

Fourth, it ignores taxes and fees. A 1% annual fee drags the safe rate down noticeably, and taxes on withdrawals mean the gross portfolio needs to be bigger than the rule suggests.

None of these assumptions is hidden, exactly. But they are rarely mentioned in the same breath as the number.

Why it still mostly works

The most striking recent evidence comes from a backtest published in September 2026 by firenum.com, which replayed a 4% withdrawal through every retirement start year from 1872 to the present using Shiller's long-run S&P 500 data. The result: the portfolio survived in 122 of 125 start years — a 97.6% success rate.

The three failures all started in 1928, 1929, or 1930. In other words, you had to retire into the Great Depression for the rule to break. Lowering the rate to 3.5% raised survival to 98.4%. Raising it to 5% dropped it to 88.8%.

That is a remarkable track record for a rule that is now over 30 years old. It survived every recession, every war, every panic — except the worst one.

The new debate: 4.7% versus 3.9%

The number is not as settled as it looks. In his 2025 book "A Richer Retirement," Bengen himself argued for 4.7%, based on a seven-asset portfolio that includes small-cap stocks and Treasury bonds. His argument: the original rule was built on limited data and a narrow portfolio, and a better-diversified one supports a higher rate.

Morningstar's 2025 State of Retirement Income report went the other direction, putting its base case at 3.9% — slightly below 4%, largely because bond yields and expected returns look less generous than the historical average.

Run at 4.7% on the long-run data, the firenum backtest shows 118 of 125 start years surviving — still strong, with failures clustered in the Depression years and a forgotten rough patch in the early 1880s. The honest reading: 4% is the cautious choice, 4.7% is defensible with diversification, and the difference between them is smaller than the difference between either and 5%.

What the rule cannot do for you

The rule's biggest blind spot is sequence-of-returns risk. If the market crashes in your first few years of retirement, withdrawing a fixed inflation-adjusted amount forces you to sell investments at the worst possible time, and the portfolio may never recover. Two retirees with the same average returns can have wildly different outcomes depending on when the bad years arrive.

It also cannot handle a retirement longer than 30 years, spending that grows faster than inflation (healthcare, for example), or the reality that most people do not spend a smooth inflation-adjusted amount every year. Real retirees spend more early, less in the middle, and more late on healthcare. The rule is a straight line drawn through a curved life.

And it says nothing about how it feels. Watching your portfolio fall 30% in year two of retirement while you keep withdrawing is psychologically brutal, even if the spreadsheet says you are fine.

How to use it without worshipping it

Treat the 4% rule as a savings target, not a withdrawal contract. "Twenty-five times spending" is an excellent answer to "how much do I need to save?" It gives you a finish line.

For the spending side, consider building in flexibility. Many planners now recommend guardrails: spend the full 4% in good years, cut back 10–20% after a bad year, and let the portfolio breathe. Research suggests flexible spending supports meaningfully higher lifetime spending than rigid rules.

Also keep your own costs low. The difference between a 1% fee and a 0.1% fee is, over 30 years, roughly the difference between a 3.5% safe rate and a 4% one. The cheapest improvement to the 4% rule is not a better number — it is a cheaper portfolio.

The flexible alternative: guardrails

The rigid version of the rule — withdraw the inflation-adjusted amount no matter what — is not how anyone actually behaves, and research suggests you should not. The alternative is guardrails: rules for when to spend more and when to pull back.

The basic version, popularized by financial planner Jonathan Guyton and later refined by Michael Kitces, works like this: start at 4%, but if a market drop pushes your withdrawal rate above a ceiling (say, 5% of the current portfolio), cut spending by 10% for the year. If a great run pushes it below a floor, give yourself a raise. You are still following a rule — just one with a thermostat instead of a fixed setting.

Studies of these dynamic strategies find they support meaningfully higher lifetime spending than the rigid 4%, because the worst damage comes from withdrawing full amounts during crashes. Skipping one vacation after a 30% drawdown does more for your portfolio than a decade of perfect asset allocation.

The catch is behavioral, not mathematical. Guardrails require you to actually cut spending when the rule says so — in the same year your portfolio just fell and the news is terrifying. Write the rules down before retirement, when you are calm. Future you, mid-crash, will not make good decisions on the fly.

The 4% rule is not a promise. It is a planning shortcut that has survived a century and a half of market history, including everything except the Great Depression. Use it to set your target, then stay flexible enough to adapt when reality arrives. That is what retirement planning actually is: a number to aim at, and the humility to adjust. Nobody ever ran out of money because their withdrawal rate was 3.8% instead of 4.2%. They ran out because they stopped paying attention.