It’s been a good century for the stock market.
From 1926 to 2025, the weighted return on all common stocks averaged 10.1% per year, according to research by Hendrik Bessenbinder, a professor at Arizona State University’s Carey School of Business.
That’s significantly higher than the 3.3% investors could have earned on U.S. Treasuries (bonds guaranteed by the U.S. government that are considered virtually risk-free) and the annual inflation rate of about 3% over the same period, Bessenbinder said.
But investing is a positive game. For people who want to build wealth, what has happened in the past 100 years is less important than what will happen in the future. And some experts believe that returns for U.S. stocks over the next decade may not be very promising.
“We see the S&P 500 index, which is heavily dominated by a handful of stocks, becoming increasingly difficult to generate long-term returns in the future,” said Quy Nguyen, chief investment officer of equity strategy at investment firm Research Affiliates. Citing factors such as stock valuations and market concentration, the firm expects the index, which is considered representative of the entire U.S. stock market, to return more than 3% annually over the next 10 years.
For those with a short time horizon, such as those thinking of retiring in the next 10 years or so, that can be a big problem. And even for those with longer investment horizons, Nguyen says the current market structure is reason enough to reconsider how they construct their portfolios.
Understand market concerns over the next 10 years
Even if we agree that the market is in for a tough year over the next 10 years, no market expert knows exactly how stocks will behave, but that doesn’t mean we should abandon U.S. stocks completely, experts say.
That’s especially true if you’re saving for a long-term goal, like retirement, which is decades away, says Sam Stovall, chief investment strategist at CFRA, an independent investment research firm. In the long run, “if you want to beat inflation and taxes, invest in stocks,” he says.
But for those keeping an eye on the market in the short term, Nguyen says there are some trends worth noting.
One is valuation. Investors determine whether a stock is worth more or less than its fair value. Investors are generally willing to pay more for a company if they believe the company will grow in the future. Investment professionals determine price tags by comparing stock prices to underlying fundamentals such as earnings, sales, and cash flow.
The more an investment is bid for future results, the higher the hurdle the stock must clear to meet investor expectations. And the hurdles are high right now, especially among stocks that lead the U.S. market, Nguyen said.
“Not only are valuations at cyclical highs, but the underlying earnings and cash flow of those valuations also appear to be at cyclical highs,” she says. “So it’s going to be increasingly difficult for[U.S. stocks]to deliver the kind of returns that they’ve had over the past decade.”
In fact, S&P 500 stocks are trading at a 42% premium to their 30-year average, according to JPMorgan research, one measure that compares stock prices to inflation-adjusted earnings.
Another concern for investors, especially those in the S&P 500, is concentration, Nguyen said. Lately, market returns have been driven by the superior returns of the so-called “Magnificent Seven” of mega-cap tech stocks, which now dominate the S&P 500. Alphabet, Amazon, Apple, Meta, Microsoft, Nvidia and Tesla stocks currently account for nearly 35% of the index.
Nguyen said that if some stocks or sectors decline in the future, overall returns could decline significantly.
“You’re increasingly exposed to a very narrow set of stocks with very narrow economic paths,” she says. “I like to have a wide variety, but in the end you’re basically putting all your eggs in one basket. Or you’re putting them in seven baskets.”
Experts say they will consider further diversification
If you invest primarily in market-cap weighted indexes such as the S&P 500, it may be worth discussing the idea of expanding your investment horizons with a financial professional, Nguyen says. That may mean exploring international names as well as smaller companies in developed and emerging markets.
Research Affiliates predicts an 8% annualized return for non-U.S. companies over the next 10 years. In comparison, the S&P 500 returned 3%. “This is a great time to think about global diversification,” Nguyen says.
Stovall says it may be worth investing in a diversified strategy that takes different approaches to weighting holdings. According to CFRA, from 1990 to 2025, the S&P 500, with all constituents equally weighted, returned 9% annually, compared to the traditional S&P’s return of 8.6%.
“In fact, the more diversified you are, the more benefits you can get,” Stovall says.
Bessenbinder’s research shows that historically investors have been rewarded for casting a wide net. An analysis of some 30,000 stocks found that just 46 stocks drove about half of the market’s returns over the past 100 years.
Even if you believe that over time as an investor, companies investing in AI will continue to drive the market higher, it’s virtually impossible to know which of the relatively small number of stocks will end up being big winners, Nguyen said.
“Not everything will have a positive return, because not everything will have a positive return,” she says. “But it’s hard to choose, so we want to be broad and diverse.”
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