The 4% Rule: How Much Can You Spend in Retirement?
Bill Bengen's 4% rule has anchored retirement planning for thirty years. Here is the math behind it, the assumptions it depends on, and the smarter ways to use it as a starting point — not a ceiling or a floor.
Where the 4% rule came from
In 1994, financial planner William Bengen ran a simple test: if a retiree pulled a fixed percentage out of a 50/50 stock-bond portfolio every year — adjusting that dollar amount up with inflation — what was the highest starting rate that survived every 30-year window in U.S. market history, including retirements that started in 1929 and 1966? The answer was about 4%.
The 'Trinity Study' a few years later replicated the result with similar conclusions. The rule went mainstream: withdraw 4% of your portfolio in year one, then increase that dollar amount by inflation each year, and you have a high probability of not running out over a 30-year retirement.
On a $1,000,000 portfolio that means $40,000 in year one. If inflation runs 3%, you withdraw $41,200 in year two, $42,436 in year three, and so on — regardless of what the market did. The portfolio absorbs the volatility; your paycheck stays roughly flat in real terms.
Why 4% and not 6% or 8%?
Long-run U.S. stock returns have averaged around 10% nominal and 7% real (after inflation). It is tempting to think you can therefore spend 6% or 7% a year forever. You cannot — because averages hide sequence-of-returns risk.
If your retirement begins with a bad decade — 2000–2009, 1966–1975, 1929–1938 — you sell shares into a falling market to fund withdrawals. Those sold shares are not there to recover when the market rebounds. The same average return produces a wildly different outcome depending on the order in which the returns arrive.
4% is the rate that survived even the worst 30-year starting point in the historical record. It is not the expected outcome; it is the floor. In most historical retirements, a 4% withdrawer died with more money than they started with.
What the rule assumes (and where it breaks)
The original rule assumes: a 30-year retirement, a portfolio of roughly 50–75% U.S. stocks and the rest in intermediate Treasuries, annual rebalancing, and tax-free accounts (it does not model taxes). Change any of those and the 'safe' rate changes too.
Retire at 55 instead of 65 and your horizon is 40+ years — safe rate drops closer to 3.3%. Hold a portfolio that is 100% bonds at today's yields — safe rate drops below 4%. Live in a high-tax state pulling from a traditional IRA — your gross withdrawal must be higher than your spending need.
On the other side: most retirees do not actually spend a flat inflation-adjusted amount. Real spending tends to decline through retirement (the 'retirement spending smile' — high early, low middle, slightly higher late from healthcare). And most retirees have Social Security, which functions as an inflation-adjusted bond that the 4% rule ignores entirely.
Dynamic withdrawal strategies
Modern retirement research has largely moved beyond a static 4%. The most common upgrade is some form of guardrails: start at 4–5%, but raise withdrawals modestly after strong market years and cut them modestly after bad ones. Guyton-Klinger guardrails are a well-known version. With small adjustments, starting rates of 5% or even higher become sustainable.
A simpler alternative: tie withdrawals to a fixed percentage of the current portfolio balance (say 4–5% every year). Your income then floats with the market — higher in good years, lower in bad — but you mathematically cannot run out. The trade-off is volatile income.
A third approach is the 'bucket' strategy: keep 1–2 years of spending in cash, 3–7 years in bonds, the rest in stocks. Spend cash first, refill from bonds, refill bonds from stocks during good years. This does not change the math, but it changes the behavior — it makes it psychologically easier to leave stocks alone during a bad year.
How to use it as a starting point
The 4% rule is best understood as a planning anchor, not a literal annual withdrawal instruction. It answers the question: roughly how big does my portfolio need to be? Multiply your annual spending need (above Social Security and other guaranteed income) by 25 — that is the portfolio size that supports a 4% withdrawal.
Need $60,000 a year from your portfolio? You need roughly $1.5 million. Need $100,000? Roughly $2.5 million. This is the same math, expressed as the '25x rule' that the FIRE community uses to define financial independence.
Once you are in retirement, treat 4% as your default and adjust from there based on your real situation: longer horizon means lower, lots of guaranteed income means higher, willingness to cut spending in bad years means meaningfully higher. The number you actually use should be the result of running your own portfolio through a simulator, not a blanket rule.
Why we use 4% as the default in our calculator
Our Retirement Savings Longevity Calculator defaults the first-year withdrawal to roughly 4% of the starting balance because that is the rate with the longest track record of surviving the worst historical retirements. It is the most defensible starting point for someone with no other information about their situation.
You should change it. If you have meaningful Social Security or a pension, you can probably withdraw more from the portfolio. If you retired early or expect to live to 100, you should probably withdraw less. If you are willing to cut spending in bad years, you can start higher. The calculator lets you slide the number — the 4% default is just where the conversation starts.
For a more realistic picture that handles sequence-of-returns risk explicitly, our Advanced Portfolio Longevity Simulator runs your actual portfolio through 1,000 Monte Carlo scenarios and shows the probability of success at any withdrawal rate.
Frequently asked questions
Is the 4% rule still safe today?
For a traditional 30-year retirement with a balanced portfolio, most modern research still finds 4% to be a reasonable starting point — sometimes a little lower (3.3–3.8%) when bond yields are very low, sometimes higher when valuations are cheap. The bigger issue is not the exact number; it is whether you stay flexible enough to adjust it in bad years.
What is the 25x rule?
Multiply your annual spending need (above guaranteed income like Social Security) by 25 to estimate the portfolio that supports a 4% withdrawal rate. $60,000 in needed portfolio income implies a $1.5M portfolio. It is the 4% rule restated as a savings target.
Does the 4% rule include Social Security?
No. The 4% rule applies only to the portfolio. Social Security, pensions, and annuities are separate guaranteed income streams that reduce how much you need from the portfolio in the first place — which is why most retirees can sustain higher portfolio withdrawal rates than 4%.
Should I retire earlier and use a lower rate?
If you retire at 55 instead of 65, your horizon stretches to 40+ years and the safe rate drops to roughly 3.3%. The trade-off is real: every percentage point lower means roughly 25% more savings required. Most early retirees pair a lower starting rate with the willingness to do part-time work in bad market years.
Why can't I just spend the average market return of 7%?
Because of sequence-of-returns risk. If the first decade of retirement is bad, you sell shares into a falling market to fund withdrawals — and those shares are not there to recover when the market rebounds. A 7% average return produces wildly different outcomes depending on the order in which the returns arrive.