The US Stock Market: Record Concentration in 2025 Exceeds 1932 Peak

The US stock market reached unprecedented levels of concentration in 2025, with the top 10 stocks representing a larger share of market value than during the 1932 peak, according to data from the Center for Research in Security Prices (CRSP), an affiliate of the University of Chicago and Morningstar.

The top 10 US stocks in 2025 represented a larger share of market value than during the 1932 peak.

Historical Market Concentration Trends

CRSP data, spanning 100 years of US stock market history, indicates that concentration levels were significantly higher from the 1920s to the late 1960s. During this period, the top 10 stocks often exceeded one-fourth of the total market value.

A period of broadening followed, lasting through the 1970s, 1980s, and 1990s. The concentration surpassed 20% again during the late 1990s tech, media, and telecom bubble, a dynamic that continued for a few years after the bubble burst in March 2000. Similar to how the 1932 concentration peak occurred after the 1929 crash, a broadening trend then began in 2003.

Concentration levels did not breach 20% of market value again until 2020. This period saw accelerated technology trends, and the substantial growth of companies like Facebook, Apple, Netflix, and Google.

Following a bear market in 2022, the launch of ChatGPT ignited an AI frenzy, leading to new levels of market concentration. Nvidia's market value reportedly reached $5 trillion by late 2025.

On October 31, 2025, the top 10 US stocks constituted 37.7% of the total market value, exceeding the previous month-end peak of 37.3% on May 31, 1932.

Parallels Between the 1920s and 2020s

Both the 1920s and 2020s were periods of significant technological transformation. In the 1920s, industries like automobiles, radio, and telecommunications experienced widespread adoption, alongside increasing electrification. Similar to the current era, wealth inequality was high, and business leaders gained celebrity status.

Credit played a substantial role in both periods. In the 1920s, consumer credit fueled purchases of cars and radios, and stock purchases were also made on credit. In December 2025, credit card debt reached record levels, and balances in margin accounts increased by 36% from December 2024 to over $1.2 trillion, according to the Financial Industry Regulatory Authority.

Speculative excess characterized both decades. The 1920s saw practices like "stock pools" and "bucket shops." The 2020s exhibit similar speculative behaviors, with mobile applications blurring the lines between investing and gambling. Historical and contemporary periods also presented conflicting expert opinions on market sustainability.

Market Concentration as a Risk Factor

Market concentration does not inherently indicate a bubble, nor is it a reliable predictor of market stress.

Historically, top-heavy markets have coincided with periods of strong returns.

For example, despite the top 10 US stocks surpassing internet bubble levels by late 2020, investors who divested at that time would have missed several years of exceptional gains, excluding a brief setback in 2022.

However, concentration can erode diversification benefits and increase market vulnerability to sentiment reversals. Beyond the weight of the top 10 stocks, sector concentration is also a relevant factor. The technology sector currently dominates the US stock market, exceeding its late 1990s share. Companies like Alphabet, Meta Platforms, and Amazon.com, though classified in different sectors, also contribute to this technological dominance.

Thematic concentration, particularly concerning AI, presents another risk. The significant investments by "hyperscalers" in AI tie their fortunes to an evolving and potentially volatile new technology. The capacity of AI for market disruption has been evident, leading to recent market rotations. Some funds have had to register as "nondiversified" with the Securities and Exchange Commission, even broad market index funds, due to these concentration levels, raising concerns about diversification requirements under the Investment Company Act of 1940.

Investment Strategies for Concentration Risk

Investors concerned about the top-heavy nature of the US stock market have several options beyond owning the broad market. These include:

• Adopting a selective approach, either independently or through active stock-pickers.
• Investing in equal-weighted stock funds.
• Tilting portfolios toward value, dividends, smaller-cap stocks, or undervalued, high-quality companies.
• Balancing broad US market exposure with other asset classes, such as international equities, bonds, and commodities.

Diversification is highlighted as a critical strategy to manage inherent market uncertainty and build resilient portfolios capable of weathering various economic scenarios. Recent market activity in 2026 has demonstrated the effectiveness of diversification.