The 4% Rule: How Much Can You Safely Withdraw in Retirement?
A single percentage, drawn from three decades of market data, still shapes how millions of people decide when they can afford to stop working.
Where the number comes from
The 4% rule traces back to research by financial planner William Bengen in 1994, later expanded by a group of professors at Trinity University in what’s commonly called the Trinity Study. Bengen tested different withdrawal rates against historical U.S. market returns going back to the 1920s, looking for the highest rate a retiree could withdraw, adjusted for inflation each year after, without running out of money over a 30-year retirement in the worst historical periods tested.
4% was the rate that held up across those worst-case historical stretches, including retirements that began right before major market downturns. The rule isn’t a guarantee about the future; it’s a conclusion drawn from how a specific set of historical scenarios actually played out, using the worst starting points found in the data rather than an average outcome across all of them.
How the math actually works
The rule says withdraw 4% of your portfolio’s value in your first year of retirement, then adjust that dollar amount for inflation every year after, regardless of what the market does. On a $750,000 portfolio, 4% comes out to $30,000 in the first year, or $2,500 a month. If inflation runs 3% that year, the second year’s withdrawal becomes $30,900, and so on, growing with inflation rather than tracking the portfolio’s actual performance year to year.
This fixed, inflation-adjusted structure is deliberate. It’s designed to provide a stable, predictable income stream rather than one that swings with the market, which matters for anyone trying to budget household expenses in retirement the same way they did while working. It also means the withdrawal amount can, in some years, exceed the actual investment income the portfolio generated that year, drawing down principal, which is expected and accounted for in the original research rather than a sign that something has gone wrong.
Why 30 years specifically
The original research targeted a 30-year retirement horizon, roughly matching a retirement starting somewhere in the mid-60s and lasting into the mid-90s. Someone retiring earlier, say in their late 40s or 50s, is planning for a retirement that could easily stretch 40 years or more, a materially different and harder problem than what the original 4% research was built to answer. For an unusually long retirement horizon, a more conservative withdrawal rate is generally considered prudent specifically because the original testing didn’t cover that longer duration of sustained withdrawals.
The debate over whether 4% still holds
The 4% rule has faced real scrutiny in recent decades. Critics point to today’s lower starting bond yields compared to the historical periods the original research was built on, longer average life expectancies that stretch the required time horizon, and higher current market valuations, all factors that could make a repeat of the historical worst-case scenarios less favorable going forward than they were in the past.
Even Bengen himself has revised his own number over time. After further research incorporating a broader mix of asset classes, he later suggested a starting rate closer to 4.7% could still be considered safe. Other researchers have landed in a different place: Morningstar’s more recent analysis, for instance, has pointed toward a more conservative figure, closer to 3.7%, for someone retiring today, citing higher current valuations and lower expected forward returns as the reason for the more cautious number. Reasonable, well-informed people land in different places on this question, which is exactly why it’s still actively debated rather than settled, and why the “right” number for you depends partly on which set of assumptions you find most convincing.
What the rule doesn’t account for
The 4% rule was built around a simplified portfolio, typically modeled as a mix of U.S. stocks and bonds, and doesn’t factor in taxes, investment fees, or other income sources like Social Security or a pension, all of which affect how much you’d actually need to withdraw from a portfolio to cover real expenses. It also doesn’t account for major, uneven spending needs, like a large healthcare expense arriving in a single year rather than spread evenly across retirement.
Sequence of returns risk is another real gap
Two retirees with identical average returns over 30 years can end up in very different positions if one experiences poor returns in the first few years of retirement and the other experiences them later, since early losses on a shrinking, actively-withdrawn portfolio are harder to recover from than the same losses hitting later, after the portfolio has had time to grow. This is called sequence of returns risk, and it’s a big part of why the original research focused on worst-case historical starting points rather than simply averaging outcomes across all possible starting years.
One practical way retirees manage this risk is by keeping one or two years of planned withdrawals in cash or a similarly stable holding, separate from the invested portfolio, so a market downturn early in retirement doesn’t force selling depressed investments to cover near-term living expenses.
Using it as a planning starting point
Despite its limitations, the 4% rule remains genuinely useful as a first approximation. Dividing a target annual retirement income by 4% gives a rough portfolio size to aim for; $60,000 a year in desired income implies a target portfolio of roughly $1.5 million under this framework. That’s a starting number to refine, not a final answer, but it’s a far more concrete starting point than guessing.
This same math is sometimes flipped around and called the “rule of 25,” since dividing by 4% is mathematically identical to multiplying annual expenses by 25. Framed either way, the underlying message is the same: the number isn’t really about the withdrawal rate itself, it’s a shorthand for how large a portfolio needs to be, relative to spending, before retirement becomes realistically sustainable.
Estimate your own numbers
Our Retirement Calculator projects a retirement balance from your current savings and contributions, then applies the 4% rule to estimate a sustainable monthly income from that projected balance, giving you a concrete starting figure to plan around.
Common questions about the 4% rule
Financial planner William Bengen introduced the concept in a 1994 research paper. It was later expanded and popularized by finance professors at Trinity University in what’s commonly referred to as the Trinity Study.
This is genuinely debated among financial researchers. Some argue current market conditions warrant a lower, more conservative starting rate, while others maintain 4% remains reasonable, especially when combined with flexible spending in years following weak market performance.
The underlying withdrawal math applies the same way regardless of account type, though 401(k)s and traditional IRAs come with required minimum distributions starting at a certain age, which can force withdrawals that don’t perfectly align with a strict 4% schedule.
This is the core risk the 4% rule was specifically designed to survive, since the original research included historical retirements that began right before major downturns. Even so, many retirees choose to build in flexibility, spending somewhat less in years immediately following a market decline, as an added safety margin beyond the rule’s baseline assumption.
Financial planner William Bengen introduced the concept in a 1994 research paper. It was later expanded by finance professors at Trinity University in what’s commonly called the Trinity Study.
This is genuinely debated. Some researchers suggest a lower, more conservative starting rate given current market conditions, while others, including Bengen himself, have suggested rates closer to 4.7% remain reasonable.
Divide your desired annual retirement income by 4%, or equivalently multiply by 25. Someone wanting $60,000 a year in retirement income would target a portfolio of roughly $1.5 million under this framework.
Sequence of returns risk means two retirees with identical average returns can end up in very different positions depending on whether poor returns hit early or late in retirement, since early losses on a withdrawn-from portfolio are harder to recover from.
No, the basic 4% rule is built around portfolio withdrawals alone and doesn’t factor in Social Security, pensions, or other income sources, which would reduce how much you actually need to withdraw from savings.
The rule of 25 is mathematically identical to the 4% rule: multiply your annual expenses by 25 to estimate the portfolio size needed to sustain that spending using a 4% withdrawal rate.
Many early retirees use a more conservative rate, since the original 4% research was built around a 30-year retirement horizon, and an early retirement can easily stretch 40 years or more.