Is the S&P 500 Broken?

Market Concentration: Past, Present, and Its Impact on Index Investing

The S&P 500 has been the workhorse for most investors over the past decades, offering affordable access to the nation’s largest and most influential companies while producing returns that have helped grow 401(k)s to support retirement dreams.

Why Has Indexing Been So Popular?

Index investing is a favored strategy for its simplicity, transparency, and cost-effectiveness. Warren Buffett, in his 2013 letter to shareholders gave this simple advice:

“Put 10% of the cash in short-term government bonds and 90% in a very low-cost S&P 500 index fund.”

By purchasing a single fund that tracks the S&P 500, investors gain exposure to hundreds of companies, diversifying risk and mirroring the market’s returns. The rise of passive investing and exchange-traded funds (ETFs) further democratized access, allowing millions to build wealth with ease through a single diversified investment.

This simple approach has been rewarded. For the past 10 years, the S&P 500 Index averaged annually 14.82% (Source: Source: BlackRock 12/31/2025). Yet, recent shifts in the composition of the S&P have begun to spark debates over whether you can continue to rely on indexing and expect a similar result; and perhaps more importantly, similar risk. The assumption of broad diversification is now being challenged by the changing structure of the index.

Market Concentration: Today vs. Historical Norms

Looking back, market concentration in the S&P 500 was much more balanced. In the 1980s and early 1990s, the largest five stocks typically made up only 10-15% of the index’s market cap. Industry leadership rotated regularly between sectors like energy, financials, and industrials. Even during the oil crisis in the 1970s, energy companies never wielded the outsized influence that today’s tech giants now hold.

Fast forward to the present, and the landscape has dramatically shifted. By the end of 2025, the top 10 stocks which include tech giants Apple, Microsoft, Alphabet, Amazon, Nvidia, Meta Platforms, and Tesla represent over 40% of the S&P 500’s market capitalization. This concentration is unprecedented.

Visualizing the Shift

• In 2014, the top 10 stocks comprised about 17% of the S&P 500 with a whopping 18% in 1994.
• By the end of 2025, the top 10 account for over 40% (Source: BlackRock, IVV holdings 12/31/2025) more than doubling in just over a decade.

Implications of Market Concentration

• Volatility and Risk: The growing dominance of a handful of mega-cap companies means the S&P 500’s performance is closely tied to their success. Should one or more of these titans falter, the entire index could suffer, regardless of how the other 490 stocks perform.
• Diversification: Investors seeking broad exposure may unwittingly find themselves heavily concentrated in technology and communications sectors, undermining the main benefit of index investing.

As a result, the S&P 500’s character has shifted from representing the broad economy to reflecting the fate of a select group of tech powerhouses.

What Could Go Wrong?

• Single Sector Shock: With technology stocks comprising such a large part of the index, a downturn in the tech sector could drag down the entire S&P 500, even if the broader economy is stable.
• Overvaluation Risk: The outsized influence of mega-cap stocks means their valuations may become stretched. If investor optimism wanes and prices correct rapidly, losses will be magnified across portfolios heavily dependent on the index.
• Lack of Representation: With small and mid-cap stocks playing a minor role, the index may not reflect growth or challenges in emerging industries, regional economies, or the broader labor market.

Risks of Diversifying Out of the S&P 500

While the concentration risk within the S&P 500 is an important consideration, diversifying away from the index carries its own set of challenges:

• Tracking Error can be a real concern as your portfolio begins to perform differently than the index. Are you okay if tech stocks continue to outperform the broader market and your portfolio?
• Diversification does not eliminate risks: Alternatives to investing in the index have their own set of risks. For those who venture farther away from the stock market, precious metals and crypto can be extremely volatile. At the end of January, silver dropped almost 30% in a single day.
• Diversification may bring more of the same. The top holding in the MSCI Emerging Markets index is another chip company, Taiwan Semiconductor, that makes up almost 12% of that index. (Source: BlackRock, EEM 12/31/2025)
• Currency and Political Risks: International diversification opens exposure to foreign exchange fluctuations, changing regulations, and geopolitical events, which can impact returns independently of U.S. market performance.
• Information Gaps: The S&P 500 benefits from rigorous financial reporting and analyst coverage. Smaller U.S. companies and many international stocks may not be as well-covered, creating potential blind spots for investors.
• Costs and Complexity: Managing a globally diversified portfolio can involve higher fees, additional tax considerations, and increased complexity compared to simply tracking the S&P 500.

Ultimately, while diversification remains a powerful tool for risk management, investors should be aware of the trade-offs. Expanding beyond the S&P 500 can provide valuable exposure and reduce overreliance on a handful of companies, but it also requires diligence, patience, and a willingness to accept different risks and returns.

Does the S&P 500 Still Serve Its Purpose?

Despite heightened concentration, the S&P 500 remains the most widely used equity index, prized for its historical returns and transparency. Many investors still consider it a bedrock of passive investing, yet those seeking true diversification should be mindful of its current limitations.

Potential Strategies for Broader Diversification

• Equal-Weighted Indexes: Giving each company the same weight can mitigate concentration risk, but may increase volatility.
• Extended Market Indexes: Including more mid- and small-cap stocks provides better market coverage.
• International Diversification: Allocating part of a portfolio to international or global equity indexes helps decrease reliance on U.S.-based mega-cap companies, offering exposure to different economic cycles, currencies, and industries.
• Sector Rotation Strategies: Actively adjusting sector exposures can address imbalances, but requires more management and higher costs.

How Professional Help Can Assist Investors

Navigating the complexities of the modern S&P 500 and understanding the broader investing landscape can be daunting. Experienced financial advisors and investment professionals offer valuable guidance tailored to individual goals, risk tolerance, and financial circumstances. They can help:

• Assess the risks and opportunities presented by current market concentration and index composition.
• Construct diversified portfolios that balance exposure across sectors, market caps, and geographies.
• Provide insight into tax implications, liquidity concerns, and regulatory changes affecting investment choices.

How to Proceed

1. Understand the risks you are taking.
   Do you own this in other investments outside of the index? Most investors are not aware how much Nvidia or Apple they may already own.
2. Determine how much risk you should be taking.
   Updating your financial plan can bring clarity to the amount of risk you should be taking. The easiest solution could be as simple as reducing the total amount you have in stocks.
3. Diversify, diversify, diversify
   Mid- and small-cap companies, value, international, and alternatives can all bring different return profiles to help if the mega cap tech stocks retreat.
4. Get the right help
   Whether it’s help with updating your financial plan or understanding the investment risk, an experienced advisor can help.

Conclusion

The S&P 500’s market concentration has reached record highs, making it an odd mix with over 40% highly concentrated in less than a dozen stocks and almost 60% in an otherwise diversified portfolio of 490 stocks. While the index remains a key tool for investors, it is crucial to understand these dynamics and consider complementary strategies such as small, mid-cap, and international investment to achieve true diversification in today’s market. The index is not “broken,” but its evolution demands a more thoughtful approach to portfolio construction, and a clear understanding of the risks and opportunities that come with diversification. Get help if you need it. For many, the “easy button” of investing in the index has worked, but the challenges are shifting and the stakes of investing your life savings are high.