The 4% retirement rule: what it means — and what it doesn’t
The 4% rule may be the most repeated retirement number — and one of the most misunderstood. The percentage is only the beginning; the assumptions underneath it are what make the rule useful or misleading.
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Short answer: the 4% rule is a starting-point framework, not a promise that 4% is right for everyone. In its classic form, you withdraw about 4% of the portfolio's starting value in the first year of retirement and then adjust that dollar amount for inflation in later years. The idea grew from historical research on how stock-and-bond portfolios survived long retirement periods.1 Modern research uses different assumptions and can produce somewhat different starting rates; Morningstar's 2025 research, for example, estimated 3.9% for its 2026 base case under a 30-year horizon, fixed inflation-adjusted spending and a 90% probability-of-success target.3
Treat 4% like the first setting on a thermostat, not a cruise-control button you press and forget. It gives you a way to start the conversation. Your retirement length, market returns, inflation, taxes, other income and willingness to adjust spending determine how well the plan holds up.
What the classic 4% rule actually says
Suppose you retire with $1,000,000. Four percent is $40,000, so the classic rule would start with a $40,000 portfolio withdrawal in year one. If inflation were 3%, the next year's withdrawal would rise to about $41,200. The important detail is that year two is not simply 4% of whatever the account happens to be worth then.
| Year | Illustrative rule | Withdrawal |
|---|---|---|
| 1 | 4% of $1,000,000 starting balance | $40,000 |
| 2 | Prior $40,000 increased by 3% inflation | $41,200 |
| 3 | Prior $41,200 increased by another 3% | $42,436 |
William Bengen's 1994 research used historical U.S. market returns and inflation to study how much a retiree could initially withdraw from a stock-and-bond portfolio without exhausting it over long historical periods. That work became the foundation for the “4% rule” shorthand used today.1 Later research commonly called the Trinity Study examined a range of withdrawal rates, portfolio mixes and retirement lengths and likewise emphasized that sustainability depends on the portfolio, horizon and spending pattern.2
Why the order of market returns matters
While you are saving and not taking money out, the order of good and bad years matters less than it does after withdrawals begin. In retirement, a large loss early on can be especially damaging because you may be selling investments to fund spending at the same time the portfolio is down. That leaves fewer dollars — and fewer shares — available to participate in a later recovery. This is called sequence-of-returns risk.4
Why “4%” and “3.9%” are not really a fight
The numbers come from different methods. Bengen's original work asked a historical question: what starting withdrawal survived the difficult retirement periods in the market history being tested? Morningstar's current research asks a forward-looking question using capital-market assumptions and Monte Carlo simulations: what starting rate meets a specified probability of success under today's assumptions?3
Morningstar's 2025 study estimated a 3.9% starting rate for a new retiree seeking a steady inflation-adjusted spending amount, a 30-year horizon and a 90% probability of having funds remaining at the end. It excludes Social Security and other nonportfolio income from the base portfolio-withdrawal calculation.3 Change the horizon, spending flexibility, portfolio or success target and the answer can change.
A difference between 4.0% and 3.9% on $1 million is only $1,000 in first-year withdrawals. The more important lesson is that neither number is a guarantee or a universal prescription.
Model the retirement runway you actually want to discuss
Terra's Retirement Reality Check lets you enter a withdrawal-rate assumption, spending target, other income, inflation and recurring investment costs. It deliberately does not label 4% — or any other number — “safe.”
Five things the 4% rule does not tell you
1. It does not know how long you will live
A 30-year retirement is a planning horizon, not a prediction. Someone retiring at 55 has a different runway than someone retiring at 72. Longer horizons generally put more pressure on a fixed spending plan.
2. It does not include your complete income picture
Social Security, pensions, annuities and part-time work can reduce how much must come from the investment portfolio. A household needing $70,000 of annual spending but receiving $45,000 from dependable outside income has a very different portfolio problem from a household that must fund the full $70,000 from investments.
3. It does not make taxes disappear
A $40,000 withdrawal from a traditional IRA is not necessarily $40,000 available to spend after taxes. Roth, traditional and taxable accounts can have different tax consequences. Withdrawal strategy and tax planning sit outside the simple 4% arithmetic.
4. It does not guarantee smooth markets or smooth inflation
The framework was built precisely because actual markets are uneven. Early losses and high inflation can make a fixed real spending pattern harder to sustain.
5. It does not require you to behave like a robot
Many retirees naturally spend less in some years and more in others. Morningstar's research finds that flexible spending approaches can support different starting withdrawal rates because the retiree is willing to adjust after market changes.5 Flexibility has a trade-off: income is less predictable.
“Safe” is an overloaded word
When retirement research calls a withdrawal rate “safe,” it usually means the strategy met a defined test — for example, the portfolio did not run out over a specific historical or simulated period. It does not mean the retiree faced no risk, maintained the same lifestyle under every condition, or was guaranteed a particular legacy.
That distinction matters because two people can reasonably want different things. One may prioritize never cutting spending. Another may accept smaller vacations after a bad market year in exchange for higher spending when markets cooperate. A third may care strongly about leaving money to heirs. There is no single percentage that captures all three goals.
Make the rule fit the retirement — not the other way around
- How many years does the portfolio reasonably need to support?
- How much essential spending is already covered by Social Security, pension or other dependable income?
- How much can spending change after a poor market year?
- What stock/bond mix are you actually comfortable holding through a downturn?
- Are taxes, healthcare costs and large one-time expenses included elsewhere in the plan?
- Is leaving a large ending balance important, or is lifetime spending the priority?
What this does not say
This article does not recommend 4%, 3.9% or any other withdrawal rate for you. It explains what those numbers mean and why research can produce different results. Retirement income is a multi-variable planning problem, and the “right” starting rate depends on assumptions that deserve to be visible.
References
- William P. Bengen — Determining Withdrawal Rates Using Historical Data, Journal of Financial Planning, October 1994. The landmark historical study behind the widely known 4% retirement-withdrawal framework. Financial Planning Association · Bengen 1994
- Philip L. Cooley, Carl M. Hubbard and Daniel T. Walz — Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable, AAII Journal, February 1998. Examines historical success rates across withdrawal rates, portfolio mixes and payout periods. AAII · Sustainable withdrawal research
- Morningstar — What's a Safe Retirement Withdrawal Rate for 2026?, based on its 2025 State of Retirement Income research. Reports a 3.9% base-case starting withdrawal rate under specified assumptions including a 30-year horizon and 90% probability-of-success target. Morningstar · 2026 withdrawal-rate research
- Morningstar — The Biggest Risk for New Retirees (Dec. 9, 2025), explaining sequence-of-returns risk when withdrawals and early market losses occur together. Morningstar · Sequence risk
- Morningstar — 4 Simple Ways to Boost Your Safe Withdrawal Rate (2026), describing the assumptions behind the 3.9% base case and how flexible spending can change retirement-withdrawal results. Morningstar · Flexible retirement spending
Common questions
Do I withdraw 4% of my current balance every year?
Does the 4% rule guarantee my money lasts 30 years?
Does Morningstar's 3.9% mean the 4% rule is obsolete?
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See the withdrawal rule inside a full cash-flow picture
Pension and Social Security can change how much your portfolio actually needs to provide. Build a year-by-year retirement income scenario rather than relying on one withdrawal percentage alone.