At first glance, the U.S. equity market appears broadly diversified, offering investors exposure to hundreds of companies spanning varied sectors and industries. But beneath the surface, market performance has become increasingly concentrated among a narrow group of mega-cap stocks.
Today, owning the S&P 500 often means taking on significant exposure to a handful of dominant companies, many of which show up repeatedly across client index funds, ETFs and retirement portfolios. As of 2025, the top 10 companies account for roughly 35%–40% of the index’s total weight, a level of concentration that challenges long-standing assumptions about how diversified it is in reality.
While these companies have driven impressive returns, their outsized influence introduces a new dynamic: portfolios are increasingly sensitive to the performance of a relatively small group of stocks. In an environment shaped by shifting interest rates, persistent inflation questions and evolving growth expectations, that concentration can create both opportunity and risk.
These companies undoubtedly belong in portfolios. But an important question remains: do clients fully understand how much of their portfolio is tied, often unintentionally, to the same names?
The S&P 500 is a market-cap weighted index, meaning the largest companies carry the greatest influence. As those companies continue to grow ever larger, their weight in the index increases, reinforcing their dominance. The result is a market that, in practice, behaves more like an “S&P 10 or 20” than a broadly diversified benchmark.
This dynamic has become even more pronounced in recent years. According to Goldman Sachs, the so-called “Magnificent Seven” stocks have accounted for a majority of the S&P 500’s returns in recent years, underscoring how narrow market leadership has become.
For investors, this creates a subtle, but important disconnect. A portfolio that appears diversified on paper may actually be heavily concentrated in a small cluster of companies driving index performance. That concentration is often amplified by overlapping exposures across multiple client investment vehicles, making it easy to underestimate the true level of risk.
High concentration on its own does not necessarily signal that a downturn is imminent. However, it does change how risk manifests in portfolios. When a small number of stocks drive a disproportionate share of returns, any shift in sentiment, earnings expectations or regulatory conditions affecting those companies can ripple through the broader market.
History offers useful context. Periods of elevated concentration – such as the late-1990s technology bubble or the pre-2008 dominance of financial stocks – demonstrate that narrow leadership can increase market fragility. While today’s market conditions differ in many ways, the underlying lesson remains: when leadership narrows, index diversification becomes less effective than it appears.
For advisors, the implication is clear. Portfolios that rely too heavily on a concentrated group of stocks may experience greater volatility than clients expect, particularly during periods of market stress.
Managing concentration risk does not require abandoning the S&P 500. But it does call for a more intentional approach to portfolio construction.
One practical strategy is to allocate capital toward underrepresented sectors such as energy, industrials, materials and healthcare. These areas tend to have lower weights in the index but can provide meaningful diversification benefits depending on market conditions and client objectives.
Another approach is to complement traditional market-cap weighted exposure with alternative weighting strategies, such as equal-weighted indices. By reducing reliance on mega-cap stocks, these strategies can help rebalance exposure, while still maintaining participation in overall market performance.
Advisors can also look beyond headline names to identify opportunities within the broader economic ecosystem. So-called “pick and shovel” companies – those providing infrastructure, materials and services that support major growth themes – offer a way to participate in long-term trends without concentrating risk in a narrow set of market leaders. This approach represents a more risk-aware way of investing in the artificial intelligence (AI) build-out being driven by leaders in the S&P 500.
In periods of heightened uncertainty, like we’ve seen recently with the war in Iran, discipline becomes even more critical. Rather than chasing concentrated areas of strong performance, advisors should prioritize maintaining alignment with a client’s established risk profile.
A thoughtful allocation strategy helps ensure that portfolios remain grounded in long-term objectives rather than short-term market trends. It also reinforces the role of the advisor as a portfolio architect – balancing opportunity with risk and helping clients navigate increasingly complex market dynamics with clarity and confidence.
The S&P 500 remains a foundational building block for portfolios, but its current concentration profile challenges the assumption that it delivers broad diversification on its own.
Advisors who recognize this shift are better positioned to proactively guide clients through it. Combining traditional index exposure with diversified strategies – whether through sector rebalancing, alternative weighting approaches or broader ecosystem investing – may help reduce reliance on a small group of dominant stocks, without sacrificing participation in equity market growth.
Diversification is no longer about how many holdings a particular portfolio contains. It requires an understanding of where risk truly resides and
Anshul Sharma is the chief investment officer at Savvy Wealth.
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