The S&P 500 hit another record close on Monday, pushing higher again during early Tuesday trading. For many investors, headlines about the index reaching new all-time highs have become so routine that it almost feels inevitable. Yet behind the optimism, a growing question lingers: how long can the rally last before a meaningful correction appears?

A Record Run That’s Making Some Investors Nervous

The U.S. stock market’s strength has been undeniable this year. Driven by surging technology stocks and resilient consumer demand, the S&P 500 index has continued its upward march despite persistent inflation concerns, global uncertainty, and rising interest rate risks.

However, not everyone sees this as a sign of lasting stability. “The S&P 500 is broken,” argues Michael DeMassa, a certified financial planner (CFP) and chartered financial analyst (CFA), who also founded Forza Wealth Management in Sarasota, Florida. His warning isn’t about the index collapsing — rather, it’s about how investors misunderstand what they actually own when they buy S&P 500 index funds.

Many retail investors assume that investing in an S&P 500 fund — through popular ETFs like SPY, VOO, or IVV — means they are getting broad diversification across the U.S. economy. But according to DeMassa, that assumption is misleading.

“The idea that the S&P 500 offers complete diversification is an illusion,” he said. “Because the index is market-cap weighted, a handful of mega-cap tech stocks dominate its performance. If those stocks stumble, the entire index suffers.”

When “Diversification” Isn’t Really Diversified

The market-capitalization weighting structure means that the largest companies — like Apple, Microsoft, and Nvidia — represent a disproportionately large share of the index. This can lead to concentration risk. For instance, the technology sector now makes up more than a quarter of the S&P 500’s total weight, creating a situation where market volatility in just a few companies can ripple across the entire fund.

DeMassa points out that this concentration creates a false sense of safety. “When investors buy the S&P 500, they believe they’re spreading risk,” he said. “In reality, they’re overexposed to the same handful of large-cap growth names driving the market.”

Indeed, while long-term investors in the S&P 500 have historically fared well, there have been long stretches where returns were disappointing. Deva Panambur, another CFP and CFA who founded Sarsi LLC in New Jersey, reminds investors of this reality. “From 2000 to 2008, the S&P 500 declined by more than 30%. Even the strongest bull markets are followed by periods of stagnation.”

Analysts Still See More Upside — For Now

Despite warnings of concentration risk, Wall Street analysts continue to forecast more gains for the index in the near future. Corporate earnings remain solid, inflation is gradually cooling, and investor sentiment is buoyant.

However, experts caution that overconfidence in a single index could expose investors to unnecessary volatility. Even if the S&P 500 continues its ascent, diversification remains a cornerstone of smart investing.

“Every investor should think about what happens if there’s a pullback,” said Panambur. “Having a broader mix of investments ensures your portfolio doesn’t move in lockstep with one narrow segment of the market.”

Exploring Broader Investment Options

For those looking to stay invested while spreading out risk, several alternatives exist. Brendan McCann, an associate manager research analyst at Morningstar, suggests considering a total market index fund instead of an S&P 500-only fund.

Unlike the S&P 500, total market funds include small-cap and mid-cap stocks — offering exposure to companies with greater growth potential outside of the large-cap space. These funds provide a more complete snapshot of the U.S. economy, from emerging innovators to established corporate giants.

Alternatively, investors can complement their existing S&P 500 positions with additional funds designed to broaden exposure. McCann highlights the Vanguard Extended Market ETF, which tracks companies not included in the S&P 500, as a good pairing option.

“The trick,” he explains, “is to balance the proportions correctly. You don’t want to double up on large-caps while neglecting small and mid-caps.”

For investors using tax-advantaged accounts like 401(k)s, switching to a total market index strategy can be even more appealing. Because these accounts aren’t subject to capital gains taxes during trading, reallocating investments carries fewer financial consequences.

Equal-Weighted Funds Offer an Alternative Approach

Another way to mitigate concentration risk is through equal-weighted S&P 500 funds, where each stock receives the same weighting rather than being determined by market capitalization. This strategy naturally tilts exposure toward smaller companies within the index, helping to counterbalance the influence of mega-caps.

However, McCann notes that equal-weighted funds often come with higher transaction costs, as they require frequent rebalancing to maintain equal proportions. “It’s a more active form of passive investing,” he said, “but it can help maintain true diversification.”

Overlapping Holdings Can Add Hidden Risk

Even when investors try to diversify, they can inadvertently increase their exposure to the same companies through overlapping holdings. For example, someone who owns both an S&P 500 ETF and a Vanguard Growth Index Fund might assume they’re diversifying — but in reality, both funds are heavily invested in the same large-cap tech names like Apple, Nvidia, and Microsoft.

This overlap amplifies rather than reduces portfolio risk. “When I construct portfolios for clients,” said Panambur, “my goal is to make sure the total allocation is more balanced than what the S&P 500 offers.”

He emphasizes that during previous downturns — such as between 2002 and 2009 — other segments of the market, including small-cap, value, international stocks, and even bonds, significantly outperformed the S&P 500. That’s why he continues to build portfolios that include exposure to all of these asset classes.

The Myth of “Set It and Forget It”

The classic “buy and hold” approach to investing in the S&P 500 was built on the assumption that the index reflects the broad U.S. economy. But with technology companies now dominating its composition, that assumption no longer holds true.

“The S&P 500 used to represent the total market,” said DeMassa. “Today, it’s increasingly concentrated in just a few sectors. If you think you’re buying the whole economy, you’re not.”

This doesn’t mean investors should abandon the index entirely — rather, they should recognize what it is and what it isn’t. It remains a powerful long-term growth engine, but it is not a one-stop solution for diversification.

Building a More Resilient Portfolio

To create a portfolio resilient to market cycles, experts recommend spreading investments across various asset classes and geographical regions. This could include:

• Small-cap and mid-cap U.S. stocks for higher growth potential
• International equities for geographic diversification
• Bonds for income and stability
• Sector-specific funds in areas like energy, healthcare, or consumer staples

Each element serves a different role, balancing growth opportunities against defensive stability. In the long run, such diversification can smooth out returns and protect against the downside risks of overconcentration.

The Bottom Line

The S&P 500’s record highs are impressive, but investors should look beyond the headlines. History shows that even the strongest bull runs eventually face corrections. Relying solely on one index — especially one dominated by a handful of tech giants — can expose investors to greater risks than they might realize.

As DeMassa puts it, “The S&P 500 is still a great tool, but it’s not the entire toolbox.” For long-term success, investors must think beyond a single benchmark, ensuring their portfolios truly reflect a diverse mix of assets that can withstand whatever the market brings next.