After studying a full century of market history, we can tell you that retirement portfolios fail for one of two reasons. A deep market crash early in retirement. Or inflation that slowly outruns a portfolio built to be "safe."
The crash problem is about timing. When you're pulling money out of a portfolio that's down 40%, you're selling more shares at the worst prices. Those losses never get the chance to recover. A working person can ride out a bear market. A retiree making withdrawals cannot, not fully.
The inflation problem is quieter, and in the data, it's actually the bigger killer. Here's a fact that surprises most people: the worst year in American history to retire wasn't 1929. It was 1966. Not because of a crash, but because it was the front door to sixteen years of inflation that slowly strangled the classic stock-and-bond portfolio.
Conventional advice asks you to pick your poison. More stocks means more crash risk. More bonds means more inflation risk. The famous "4% rule" is simply the spending level low enough to survive that compromise.
We spent months testing a different question: what if you didn't have to compromise?
Here's the short version of what we found. Across a full century of market history, a simple trend-following strategy beat every static portfolio we tested — a higher worst-case withdrawal rate, better odds of success at every realistic spending level, crashes nearly half as deep, and just as much wealth at the end. The rest of this article walks you through those numbers, and through the catch that comes with them.
If you've heard of the 4% rule, you've heard of William Bengen's work, even if you've never heard his name. In 1994, Bengen published the study that created the rule. He took every retirement starting year from 1926 forward, ran a 50/50 portfolio of US stocks and intermediate-term Treasuries (government bonds maturing in roughly five years) through each one, and asked a simple question: what's the most a retiree could have withdrawn, adjusted for inflation every year, without running out of money in 30 years, even with the worst possible timing?
His answer: about 4.15%. In dollar terms, a couple retiring with $2 million could have withdrawn roughly $83,000 in their first year, given themselves a cost-of-living raise every year after, and never run out of money in 30 years. Even with the worst retirement timing of the century. That number became the foundation of modern retirement planning.
Before testing anything new, we rebuilt his study exactly. Same data, same rules, same math. We verified our version against the worked example in his own paper, to the dollar. Then we extended it with 33 more years of real market history, through 2025.
Two things came out of that. First, the 4% rule held up. Three more decades of data (including the dot-com bust, 2008, and 2022) didn't break it. Second, Bengen was actually conservative. His original study had to estimate a few future years that hadn't happened yet. Replace his estimates with what the market actually did, and his worst-case number rises to 4.30%. The retiree he worried about most — the person who retired in 1966 — made it 38 years at a 4% withdrawal, not the 33 he projected.
That gave us a trustworthy baseline. Then we ran one more strategy through the exact same test.
The approach we tested is called trend following, and it's deliberately simple. Here's the entire strategy:
At the end of every month, compare the S&P 500's closing price to its average closing price over the past 12 months.
That's it. No predictions, no economic forecasts, no judgment calls. One look per month, and in practice, about one trade per year. The idea isn't to outsmart the market. It's to own stocks when the tide is rising and step aside when it isn't.
Here's what that looked like in practice. At the end of December 2007, the S&P 500 closed below its 12-month average. The rule moved the portfolio into Treasuries and kept it there through essentially all of 2008, while stocks lost 37%. Then, once the recovery pushed prices back above trend in 2009, it moved back into stocks. No forecasting, no headlines, no gut calls. Just the rule.
This isn't something we invented for a backtest. It's the same logic behind the systematic strategy we run in real client portfolios today, and trend following itself has decades of published research behind it. Everything else in our test (the withdrawal rules, the inflation adjustments, the bond type, the retirement years) stayed exactly as Bengen designed it. Same race, one new runner — and as you're about to see, the new runner won.
Start with what matters most: how much you can actually spend. On a $2 million portfolio, the difference between withdrawing 4% and 6% is $80,000 a year versus $120,000 a year. That's not a rounding error — that's a different retirement.
Here's the percentage of all historical 30-year retirements that succeeded, meaning the money lasted the full 30 years, at each spending level:
Read that middle row again. At $120,000 a year, the classic balanced portfolio worked about 6 times out of 10. Historically, a gamble. The trend strategy worked almost 9 times out of 10.
Just as important is how each portfolio fails as spending rises. Push the 50/50 past 5% and its success rate falls off a cliff — 83%, then 61%, then a coin flip. The trend strategy declines gently. One of these is a tightrope. The other has guardrails.
If you want to retire in your 40s or 50s, your money might need to last 40 or 50 years. This is exactly where conventional portfolios quietly fall apart: a five-decade retirement gives inflation five decades to find you. Standard advice for early retirees is to cut spending down to 3.25–3.5% for that reason.
The trend strategy barely notices the longer horizon:
Put real dollars on that middle number. Picture retiring at 50 with $3 million and spending $150,000 a year, raised for inflation, for five full decades. Historically, the trend approach carried that plan through 94% of all start dates. The classic balanced portfolio made it less than half the time. The haircut early retirees are told to take isn't a law of nature. It's the price of a static portfolio.
Why does the gap widen with time? Because long retirements give the market more chances to serve up a killer decade. The balanced portfolio's killer, a long stretch of inflation, shows up regularly in history. The trend strategy's killer is much rarer. More years means more danger for one and not much more for the other.
Over the past century, the deepest peak-to-bottom losses for each approach:
To put those in dollars: an 83% decline turns $2 million into $340,000. A 41% decline leaves about $1.2 million. For someone withdrawing $100,000 a year, one of those is a frightening stretch. The other is the end of the plan.
The trend strategy's edge comes from refusing to ride extended bear markets. It spent most of 1930–1932 in Treasuries. It was out of stocks for essentially all of 2008. It sidestepped the worst of the dot-com collapse. For a retiree, avoided losses count double — a drawdown you don't experience is a drawdown you're not withdrawing from.
But you don't have to take the backtest's word for it, because the modern era already ran the experiment with real retirees. Consider everyone who retired between 1996 and 2025:
At a 5% withdrawal, people who retired in 1999 or 2000 holding stock-heavy static portfolios have already run out of money. Not hypothetically. Their portfolios failed in years 17 through 24. At 6%, every static mix for the 1998–2001 retirees has failed.
The trend strategy? Zero failures. Not one, at any spending level we tested, up to 8%. The 2000 retiree — the worst modern start date — still holds about 2.7 times their original purchasing power today, after 26 years of withdrawals.
Here's the part most risk-management strategies get wrong. Anything that reduces crash risk usually does it by holding fewer stocks, and fewer stocks means less protection against inflation, the retiree's bigger long-run enemy.
The trend strategy solves this differently. Because it has an exit plan for bear markets, it can afford to hold 100% stocks roughly 70% of the time, far more equity exposure than any balanced portfolio. Stocks are the one mainstream asset that has historically outrun inflation over long periods. The strategy gets that inflation protection without paying the usual price in crash risk.
Go back to 1966, the worst retirement year in American history. Consumer prices nearly tripled over the following fifteen years. A household that needed $100,000 a year at the start needed close to $300,000 by 1981 just to live the same life. Bonds didn't save that retiree, because bonds were the problem: they lost ground to inflation year after year. Our data shows the 1966 retiree could have sustained a withdrawal rate above 5% with the trend approach: in Treasuries during the crashes of 1969–1974, in stocks through the inflationary recoveries. The portfolio that beat the inflation era wasn't the one that hid from stocks. It was the one that knew when to hold them.
Safety usually costs growth. Not here. And this is precisely why a trend approach sits at the heart of how we manage portfolios: it's one of the few places in investing where the historical record says you don't have to choose.
Across all historical retirements, the trend strategy's typical outcome matched a 100% stock portfolio almost exactly (the highest wealth-building result in the study) while taking half the maximum drawdown. In plain terms: the floor of a balanced fund with the ceiling of a stock fund.
The modern record says the same thing. Of everyone who retired since 1996 and spent 5% a year, 93% of trend-strategy retirees are sitting above their original purchasing power today — their portfolios have grown faster than inflation, even after three decades of withdrawals. For the classic 50/50, that number is 37%. Most balanced-portfolio retirees of the modern era are slowly going backward and may not realize it.
For families thinking beyond their own retirement (inheritance, grandchildren, charitable giving), that difference compounds into an entirely different legacy.
If this strategy were free money, everyone would run it. It isn't, and you should know exactly what it costs before you take any of the numbers above seriously.
It can't dodge fast crashes. The strategy took the October 1987 crash in full — the market fell too quickly for a monthly signal to react. Its protection works against long bear markets, not sudden ones.
It pays a tax in whipsaw markets. When the market drops and then snaps back quickly, the strategy can end up selling low and buying back in higher. 2020 is the honest example: the rule stepped out of stocks at the end of February, sidestepped the worst of the March crash, then watched much of the rebound from the sidelines before getting back in that June. That's not a flaw to be fixed; it's the permanent price of the insurance. Its worst historical retiree (1939, a choppy sideways decade) still did better than every static portfolio's worst retiree — but the cost is real.
The strategy is simple. The discipline isn't. Every result above assumes the rule was followed mechanically, every month, for decades, including the years it looked foolish. In our experience, that's the single hardest part, and it's where a systematic process (or an advisor running one) earns its keep.
Two practical notes: above roughly an 8% withdrawal rate, no defensive strategy saves you — only raw growth can, and stocks win. And because each switch is a taxable event, this approach belongs in IRAs and other tax-advantaged accounts.
The 4% rule isn't wrong. Our research confirms it — Bengen's work has held up for three decades, and if anything, he was conservative. But the 4% rule is the answer to a specific question: how little must I spend so that a static portfolio survives the worst of history?
Change the portfolio from static to systematic, and the answer changes. Across a century of data, a simple monthly trend rule raised the floor, roughly doubled the odds of success at higher spending levels, cut the worst drawdown nearly in half versus stocks, and matched an all-stock portfolio's wealth creation. It defended against both of a retiree's enemies, crashes and inflation, instead of trading one for the other.
We didn't run this research to publish a paper. We ran it because our clients ask us real questions: Can I retire at 52? Can we spend $150,000 a year? Will this survive another 1970s? Those questions deserve answers backed by evidence, not rules of thumb. This is the evidence base we plan with.
If you're approaching retirement, or hoping to get there early, and you'd like to see what your portfolio and spending plan look like against a century of history, that's exactly the work we do. Schedule a call and we'll walk through it together.
All results above are hypothetical, backtested performance — no client earned these returns. Figures are gross of taxes, advisory fees, and trading costs. The trend strategy trades roughly once per year, so modern trading costs are small, but trading costs in earlier decades were substantial and would have meaningfully reduced the early-period results shown. Trend-following approaches are generally best suited to tax-advantaged accounts, since each switch is a taxable event in a brokerage account.
Results are based on US market data (historically the world's best-performing major stock market) using January retirement start dates; other start months can produce modestly different outcomes. One hundred years of history contains only a handful of truly independent 30-year retirement periods, so success percentages describe how strategies performed along one historical path; they are not probabilities of future outcomes. The static-portfolio analysis replicates William Bengen's published 1994 methodology; the trend-following comparison is Strong Wealth's own research and was not part of his study. The trend strategy has trailed its own historical average since 2015. Past performance does not guarantee future results. Nothing here is individualized investment advice; whether any strategy is appropriate depends on your complete financial situation.