The 4% rule: what it is and where it falls short

The "4% rule" is probably the best-known idea in retirement income planning. It is often repeated as if it were a law of finance. It is better understood as one researcher's finding about a particular set of historical data, built on particular assumptions. Knowing what it says, and what it does not say, makes it more useful.

What the rule says

The idea traces to a 1994 study by financial planner William Bengen. He examined historical periods and proposed an initial withdrawal of about 4% of the starting balance, adjusted for inflation each year, over a 30-year horizon.

The pattern works like this:

1. In the first year of retirement, withdraw 4% of the portfolio's value.
2. In each later year, withdraw the same dollar amount as the year before, increased by that year's inflation.

The percentage applies only once, at the start. After that, the withdrawal follows prices, not the portfolio.

This is a research finding about the past. It is not a rule that predicts future results, and it does not mean that 4% or any other withdrawal rate is safe or sufficient for a particular retiree.

A hypothetical example

The following numbers are made up to show the mechanics. They are not a forecast.

Suppose someone retires with $500,000. Four percent of that is $20,000, which is the first year's withdrawal. Suppose prices then rise 3%. The second year's withdrawal is $20,600, whether the portfolio is now worth $450,000 or $550,000. If prices rise 2% the next year, the third withdrawal is $21,012.

Two things stand out. Spending power stays level, which is the point of the method. And the withdrawal ignores what the market has done, which is the source of most of the criticism.

The assumptions underneath

A finding of this kind depends on the conditions that were studied.

• A 30-year retirement. Someone retiring at 55 may need money for much longer. Someone retiring at 75 may be planning for a shorter span.
• An invested portfolio. The idea is about withdrawals from a portfolio that stays invested. A different asset allocation, meaning the mix of stocks, bonds and cash, may behave very differently.
• Past market history. The study looked backward at particular historical periods. The future is under no obligation to resemble them.
• Fees and taxes. The headline percentage is a withdrawal amount, not a spending amount. Investment costs and income tax both come out of real portfolios. The guide on what 401(k) fees cost shows how fees reduce a balance over time.
• Steady, inflation-adjusted spending. Real spending often changes: higher in the early active years for some, higher later because of health costs for others.

Where it falls short

It is backward-looking. The rule reports what a study of the past found. It says nothing certain about whether the same pattern will hold in the future, and no withdrawal rate can be called safe in advance.

It is rigid. Few people would keep raising their withdrawals on schedule during a deep market decline, and few would refuse to spend more after a long stretch of strong results. A formula that never responds to the portfolio can lead to cutting it too close in bad conditions or leaving a great deal unspent in good ones.

It is exposed to bad timing. Poor results in the first years of retirement can do more damage than the same results later, because withdrawals are being taken from a shrinking balance. This is called sequence-of-returns risk.

It ignores required withdrawals. Federal law generally requires withdrawals from traditional IRAs and workplace plans to begin at age 73, with a later starting age scheduled for people born in 1960 or later. The required amount is based on the account balance and an IRS life-expectancy table. That amount is set by the IRS formula, not by any withdrawal rule. See RMD basics.

It treats inflation as the only adjustment. Investor.gov explains that inflation reduces purchasing power. The rule addresses that risk directly, but a retiree's personal costs may rise faster or slower than the general price level.

How people adapt the idea

Because of these limits, many retirees and planners treat 4% as a reference point and then build in flexibility. Some common variations:

• A percentage of the current balance. Withdrawing a fixed percentage of whatever the portfolio is worth each year means the account cannot be emptied by the formula, but income rises and falls with the market.
• Guardrails. A starting withdrawal is raised with inflation in most years, but trimmed if the portfolio falls below a set level and increased if it rises above another.
• Skipping the raise. Some people forgo the inflation increase in any year after the portfolio has lost value.
• A spending floor from other sources. Covering essential bills with Social Security, a pension or an annuity leaves portfolio withdrawals to pay for expenses that can be reduced if necessary.

Each approach trades one thing for another, usually predictability of income against the chance of depleting savings. None removes uncertainty, and none can be said in advance to work better than the others.

Questions worth asking

For anyone using a withdrawal rate to plan, a few questions help put the number in context.

• How many years might withdrawals have to last?
• How much of the budget is essential, and how much could be reduced in a bad year?
• What other income arrives regardless of the markets?
• Are the figures before or after fees and taxes?

The 4% rule remains a common reference point for seeing roughly how a lump sum relates to annual income. It is one input to a retirement income plan, which many people review and adjust over time instead of relying on any single percentage.