Diversification can help mitigate risk in today's concentrated market

Many investors assume they’re diversified because they own a mix of stocks and bonds or because they hold a broad market index fund. But true diversification is not just about the number of investments in a portfolio. What matters is whether those investments are exposed to different sources of risk and return, especially when markets become volatile.

That volatility has been on display in recent weeks as investors reacted to shifting expectations for the path of interest rates. As widely expected, the Federal Reserve raised rates for the first time in more than three years, by a quarter-percentage-point, at its September 16 meeting. At the same time, Treasury yields have surged higher – with the 10-year yield crossing 5% on September 14, for only the second time since the 2008 financial crisis.

That distinction matters today. As of September 2026, the top 10 S&P 500 companies represent roughly 38% of the index’s total market capitalization, exceeding the dot-com era leaders by about 10 percentage points. With so much of the index concentrated in a relatively small group of large-cap tech companies, investors may be more exposed to a narrow set of market drivers than they realize.

Diversification cannot guarantee gains or protect against losses, but it can help reduce the impact of underperformance by any one company, sector or asset class. The goal is not to own everything, but to build a portfolio where each component has a clear purpose and where risk is spread intentionally across different opportunities, strategies and market environments.

Why portfolio diversification matters – especially in today’s concentrated market

Diversification is the practice of spreading your investments across different sources of return and risk. In plain terms, it means building a portfolio that is not too dependent on any single company, sector, asset class or market theme. That overreliance is known as concentration risk – the risk that too much of a portfolio’s performance depends on a narrow set of investments or market drivers.

Diversification matters because markets do not reward the same exposures in every environment. Growth, inflation, interest rates, earnings expectations and investor sentiment can all favor different parts of a portfolio at different times. And while diversification does not guarantee a profit or protect against loss, it may help reduce the impact of any single area’s underperformance – which in turn can support more consistent returns over time.

The need to look beneath the surface is especially relevant today. Artificial intelligence (AI) is reshaping where investors see growth, where companies are directing capital spending and where future profits are expected to compound. Much of that attention has centered on the so-called Magnificent Seven stocks – Alphabet, Amazon, Apple, Meta, Microsoft, NVIDIA and Tesla – which have played an outsized role in driving market leadership. This does not make those companies unattractive or inappropriate to own, but it does mean many portfolios may be more exposed to a narrow set of AI-linked and mega-cap growth themes than investors realize.

The AI trade in particular has shown how quickly market sentiment can swing on new headlines. For example, chip stocks fell sharply after several CEOs of major AI companies joined together in calling for a slowdown in development and more safeguards. This highlights how concentrated positioning can amplify market moves.

Sector exposure tells a similar story. Information technology represents nearly 38% of the S&P 500, and when combined with communication services – where several large digital platform companies are classified – the two sectors account for nearly half of the index. For investors, the key question is not whether to avoid those areas, but whether the rest of their portfolio provides enough balance should market leadership shift, earnings expectations reset or highly correlated holdings begin moving in the same direction.

Diversifying beyond stocks and bonds: The role of different asset classes

While stocks and bonds are often the foundation of a diversified portfolio, they are not the only tools investors can use. Equities can provide long-term growth potential, but they also tend to come with greater volatility. Fixed-income investments can offer stability and the potential for capital preservation, but bonds can still be affected by changes in interest rates, inflation and credit conditions. A diversified portfolio starts with understanding the role each asset class is meant to play.

Cash and cash equivalents can serve a purpose, too, even if they are not typically viewed as long-term growth assets. They may provide liquidity, flexibility and a source of stability during periods of market stress. For investors with near-term spending needs, cash can help reduce the need to sell other assets at unfavorable times. But holding too much cash has its own risks as well, including the potential for inflation to erode purchasing power over time.

Some investors may consider alternatives, such as private credit, private equity, real estate, infrastructure, commodities or hedge fund strategies. These investments may behave differently from traditional public stocks and bonds, but they can also involve limited liquidity, higher fees, added complexity, valuation uncertainty, eligibility requirements and different risk profiles.

Consider viewing asset classes as tools with distinct roles, not as boxes to check. The right mix depends on an individual investor’s goals, time horizon, liquidity needs, tax situation and risk tolerance.

How to diversify within equities, fixed income and other asset classes

Diversification does not stop at deciding how much to allocate to stocks, bonds, cash or alternatives. Investors can own multiple funds or many securities and still have meaningful overlap if those holdings are concentrated in the same companies, sectors, regions or investment styles. That is why investors need to look “under the hood” – not just at the overall number of funds or securities they own.

Within equities, investors can diversify by sector, market cap, geography, investment style and individual company exposure. A portfolio that combines small-, mid- and large-cap stocks; U.S. and international equities; and a mix of growth, value, quality, dividend or low-volatility strategies may be less dependent on any one part of the market. This can be especially important when broad U.S. equity exposure is more concentrated than investors may expect.

Fixed income can be diversified, too. Bonds vary by duration, credit quality, issuer type, geography and tax treatment, and each of those characteristics can affect how bonds perform when rates, inflation or credit conditions change. The same principle applies to alternatives: Different strategies, managers, liquidity terms and return drivers can play very different roles in a portfolio.

A useful first step is to check for fund overlap. Multiple exchange-traded funds (ETFs) or mutual funds may own many of the same mega-cap companies or respond to the same market forces, reducing the diversification benefit investors expect. Reviewing underlying holdings and risk exposures can help reveal whether a portfolio is truly diversified.

Using alternatives and structured products to expand the diversification toolkit

For some investors, diversification may mean pursuing instruments beyond traditional stocks, bonds and cash. Alternatives and structured products may help address specific objectives, such as seeking differentiated return streams, hedging concentrated exposure, managing volatility or generating more customized outcomes. While these tools are not necessarily appropriate for every portfolio, they may play a role when employed thoughtfully.

Alternatives can be driven by different return factors than public markets. Structured products are investments designed to provide features such as income or a degree of protection against market declines. These benefits often come with trade-offs, such as limiting gains if markets rise sharply.

The common thread is customization: These tools can change how a portfolio reacts to different market conditions. But they also come with added complexity, including liquidity limits, counterparty risk, embedded costs, tax considerations, valuation uncertainty and suitability requirements. Investors should understand both the risk they are trying to reduce and the risk they may be adding before incorporating such instruments into a diversification strategy.

The bottom line: Why rebalancing is essential to maintaining a diversified portfolio

Diversification is not a one-time decision. As markets move, a portfolio’s allocation can drift away from its original targets. If one asset class, sector or group of stocks performs especially well, it may become a larger share of the portfolio than intended – potentially increasing risk without the investor making an active choice.

Rebalancing helps bring the portfolio back toward its target allocation. That may mean trimming areas that have grown too large and adding to areas that have become underrepresented. The goal is not to time the market, but to maintain the level of risk and diversification that aligns with your objectives.

Investors can rebalance in several ways: on a set schedule, such as quarterly or annually; when allocations move beyond predetermined thresholds; after major market moves; or when personal circumstances, cash flow needs or goals change. In taxable accounts, rebalancing should also be done with tax considerations in mind, since selling investments that have appreciated may generate capital gains.

A diversified portfolio is not meant to avoid risk altogether. Rather, it is meant to help investors approach risk more deliberately. By spreading exposure across and within asset classes, considering additional tools where appropriate and rebalancing over time, investors can build portfolios that are better aligned with their goals, time horizon, liquidity needs and tolerance for volatility. Working with a qualified financial advisor can help identify hidden concentrations and determine which diversification levers may be appropriate.

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