The 4% Rule Is a Starting Guardrail, Not a Law

01 What the 4% rule actually says

The 4% rule says you can withdraw 4% of your portfolio in the first year of retirement, increase that dollar amount with inflation each year afterwards, and have a high probability of the money lasting thirty years.

Two features of that sentence are routinely lost. The percentage applies once, to the starting balance — it is not 4% of whatever the portfolio happens to be worth each year. And the increases are in dollars indexed to inflation, so the withdrawal is designed to hold its purchasing power rather than to track the market.

It came from William Bengen's 1994 study of US market history, refined by the Trinity study, and it was calibrated against the worst sequences in that record rather than the average. A retiree starting in 1966 needed it; most others could have withdrawn considerably more and died with a large surplus.

The assumptions underneath are specific: a roughly 50-75% stock allocation, US market returns, a thirty-year horizon, and no investment fees. Change any of those and the number moves. A forty-year retirement, a globally diversified portfolio, or a 1% advisory fee each argue for something lower — as does the order in which returns arrive, which is what the rule was calibrated against in the first place.

What it is genuinely good for is sizing a goal. Multiply the income your portfolio must produce by 25 and you have a target — which is the most useful thing a single number can do, and considerably more than it was ever meant to do beyond that.

The rule is narrower and more precise than its reputation. In year one you withdraw 4% of your portfolio. In every year after, you ignore the balance entirely and instead take last year's dollar amount, bumped up by inflation. So a $1,000,000 portfolio gives $40,000 in year one; if inflation runs 3%, year two is $41,200 — regardless of whether the market rose or fell.

That distinction is the whole article. "4% of the balance every year" is a different strategy: it can never fully run out, but your income lurches with the market. Bengen's rule fixes your real income and asks whether the portfolio can sustain it. The flip side of a stable income is that the portfolio carries all the risk — which is why the sequence of returns matters so much.

One useful consequence: because 4% is one twenty-fifth, the rule implies a portfolio of roughly 25× your first-year spending. Want $60,000 a year? The rule points at about $1.5 million.

Source: Bengen, W. (1994), "Determining Withdrawal Rates Using Historical Data," Journal of Financial Planning

02 Where it came from: Bengen and the Trinity study

The number isn't a guess. In 1994, financial planner William Bengen ran historical US stock and bond returns through every rolling 30-year retirement window he could find and asked: what's the highest starting withdrawal rate that never depleted the portfolio, even for someone unlucky enough to retire right before a crash? His answer was about 4% (he called it "SafeMax"), assuming a portfolio of roughly 50–75% stocks.

Four years later, three Trinity University professors — Cooley, Hubbard, and Walz — published what became known as the Trinity study (1998). Using a similar historical approach across various stock/bond mixes, they reported success rates: a 4% inflation-adjusted withdrawal succeeded in the large majority of 30-year periods for stock-heavy portfolios. Two independent methods, landing in the same neighborhood, is why 4% stuck.

The rule is generally understood as withdrawing 4% each year, and that is not what it says. The percentage is applied once, to the starting balance, and the resulting dollar amount is then increased with inflation — which behaves very differently from taking 4% of a fluctuating portfolio and is the source of most of the confusion about whether it "works".

Source: Cooley, Hubbard & Walz (1998), "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable," AAII Journal

03 Worked example: your first-year withdrawal

Before the debate about the right rate, it helps to see what a rate even produces. Below, enter your portfolio and a withdrawal rate; the box shows the first-year income that rate implies, annually and monthly. The default is 4%. This is the easy part of the math — the hard parts come after.

Notice what the box can't tell you: whether that income survives. A $1,000,000 portfolio at 4% produces $40,000 in year one and about $3,333 a month — but the same $40,000 start can last 40 years or run dry in 22, depending entirely on when the bad returns arrive. That's the next chapter.

On the defaults above, the worked example returns $40,000. At 4%, this is near or below Bengen’s historical SafeMax — a reasonable starting guardrail.

04 Sequence risk — the real threat

Here's the fact that reframes everything: two retirees can earn the exact same average return over 30 years and end up in completely different places, purely because of the order. The one who hits a deep bear market in years one through five — while pulling money out — sells shares cheap, locks in the loss, and may never recover. The one who gets the same bad years near the end is usually fine, because the early growth gave the portfolio a cushion.

This is sequence-of-returns risk, and it's why "the 4% rule survived history" is true but incomplete. It survived because Bengen tested the worst starting years too. But on the unlucky paths, the portfolio spent its first decade shrinking, and that's where plans actually fail. Averages hide it; sequences expose it.

The practical defenses all attack the early years: hold a cash or short-bond buffer to avoid selling stocks into a crash, keep enough equities for long-run growth, and — most importantly — be willing to adjust withdrawals when markets fall.

05 3% vs 4% vs 5% and the modern debate

So is 4% still the right number? Honestly, the research has split into a range. After years of low bond yields and high valuations, Morningstar's analysts suggested a safer starting figure closer to 3.3%–3.5% for a 30-year horizon. Meanwhile Bengen himself revised upward over time — adding more asset classes (like small-cap and international stocks) pushed his estimate of the safe rate toward roughly 4.5%–4.7%. Same question, defensible answers a full percentage point apart.

The table makes the trade concrete on a $1,000,000 portfolio. A higher rate buys more income today and a smaller required nest egg — and pays for it with higher depletion risk over 30 years.

Notice the rate isn't really one decision — it's a bundle of assumptions about your horizon, your asset mix, and how much income flexibility you have. Picking 3% vs 5% in isolation is choosing an answer before you've stated the question.

Sources: Bengen, W. (1994), Journal of Financial Planning; Morningstar's "State of Retirement Income" analyses (2021–2024), which suggested starting rates near 3.3%–3.5% in low-yield conditions.

06 Guardrails instead of a fixed rate

The simplest version needs no formal system at all: skip the inflation increase in any year the portfolio fell. That is a real-terms cut of two or three percent, it requires no calculation, and it captures most of the benefit.

What makes any of them work is deciding the rule in advance. A retiree who improvises a spending cut during a crash rarely makes it, and one who has written down what happens after a down year usually does.

None of this means the 4% rule is wrong. It means 4% is the starting point of a conversation, not the end of one — a way to size the goal, after which real planning takes over.

The fix for sequence risk isn't picking a smarter single number — it's giving up the single number. Dynamic, or "guardrail," strategies adjust withdrawals to markets. The best-known is Guyton-Klinger: you set an initial rate, then apply rules that cut spending after a bad year (when your withdrawal rate drifts too high) and let you raise it after good years. Spending flexes instead of the portfolio silently failing.

The payoff is real. Because you're willing to trim in downturns, guardrail approaches let many retirees start a bit higher than a static 4% — often in the high-4s or low-5s — while keeping depletion risk in check. You trade a perfectly smooth income for a much more durable one. For most people that's the right trade, because a temporary cut in a bad year is far less painful than running out at 85.