A long-running rally, led by a handful of the largest companies, has prompted concerns that the U.S. stock market is dependent on the fate of just a few mega-capitalization companies. The central question is, “What happens when optimism about the current market leaders wanes?” History suggests that the leaderboard will change, and the market will adapt.
Stock market concentration ebbs and flows: Leaders change across cycles
The largest companies naturally command attention, but their dominance has never been permanent. Consider how the market has evolved from the era of heavy-industry giants like Standard Oil of New Jersey (now Exxon) and General Motors to today’s technology leaders.
Change comes—even for the largest companies
Notes: Data are quarterly as of December 31, 2025. For details about our methodology, please refer to the notes at the bottom of this article.
Sources: Vanguard calculations using CRSP Research Data Products from Morningstar.
Changing economic conditions and the process of creative destruction lead to the growth and decline of companies and industries. In the late 1950s, for example, the U.S. equity market saw levels of concentration like those of today, with the 10 largest companies accounting for roughly 32% of the market’s capitalization. As of December 2025, the same companies made up just 2% of the market.
Conversely, today’s U.S. stock market leaders entered the market with negligible weightings and have grown into dominant positions. Apple, for example, went public in 1980, accounting initially for just 0.1% of the market. It accounted for 6.7% as of December 2025, trailing only NVIDIA (7.6%).
The relationship between market concentration and long-term market performance
Concerns about stock market concentration may revolve around the assumption that the eventual decline of current leaders will derail long-term market returns. The historical record suggests otherwise.
As former leaders have given way to new innovators, their decline in weight has not led to a corresponding long-term decline of the U.S. equity market. To the contrary, the emergence of today’s market leaders has filled the gap—a “handover” that has helped the U.S. equity market to deliver long-term gains. Since 1958, the U.S. equity market has delivered an annualized return of roughly 11%.1
Even inflation-adjusted returns are strong, measuring approximately 7%.2
To be clear, investors have had to endure rough patches to capture those long-term gains.
The long-term growth of the U.S. stock market
Notes: Data reflect quarterly total returns for the CRSP NYSE/NYSE American/NASDAQ/NYSE Arca Value-Weighted Market Index, as provided by CRSP, between 1958 and 2025. Bear markets are defined as periods in which U.S. stocks decline 20% or more from the end of any given quarter. Past performance is no guarantee of future results. The performance of an index is not an exact representation of any particular investment, as you cannot invest directly in an index.
Sources: Vanguard calculations using CRSP Research Data Products from Morningstar.
The stock market reflects a changing economy
“The market’s shifting composition is a feature, not a flaw,” said Erich Pingel, an analyst in Vanguard Investment Strategy Group. “As industries rise and fall, investors adapt, causing the market to continuously reflect the structure of the economy.”
Economic changes shape stock market industry exposures
Notes: Data are quarterly as of December 31, 2025. For details about our methodology, please refer to the notes at the bottom of this article.
Sources: Vanguard calculations using CRSP Research Data Products from Morningstar and the Kenneth R. French Data Library.
“Technology companies’ current dominant share of the U.S. market is striking but not entirely unprecedented,” Pingel said. ”There have been periods in history when oil and industrial companies accounted for similar shares of the U.S. stock market, notably in the 1940s and 1960s.”
Today’s winners may be tomorrow’s losers—but history suggests that equity markets will endure
At some point, the identity of the market’s largest companies will change.
The adjustment may come with a sharp downturn, an extended period of subdued gains, or something in between.
“It’s hard to know who tomorrow’s winners will be or when they’ll emerge, but if you own the entire market, chances are you already own them,” said Rodney Comegys, chief investment officer, Vanguard Capital Management, and head of Global Equity. “Even when markets appear concentrated, history reinforces the value of diversified exposure to capture economic progress. Jack Bogle’s message of ‘owning the haystack’ remains as relevant today as it was 50 years ago.”
Notes:
All investing is subject to risk, including possible loss of principal.
Diversification does not ensure a profit or protect against a loss.
We identify the 1958 cohort of stocks by ranking them by their proportional percentage of total market capitalization on December 31, 1957. We then track their corresponding quarterly percentage share of the total market capitalization of the CRSP U.S. stock market database over the subsequent years. If a stock is delisted or goes bankrupt, we assume the subsequent weight for that stock is 0%; if it is merged, we locate the successor company PERMCO (a unique permanent company identifier created by CRSP to track companies) in the CRSP dataset and then utilize the successor company weight for the forward periods. The one exception is AT&T, which split into several regional firms in the mid-1980s; in this case we only track the primary parent stock. We repeat this process for the 2025 cohort but track the market capitalization share backward in time from December 31, 2025. We select 1958 because the S&P 500 Index was introduced in 1957, and our goal is to track the matching period of the S&P 500 Index. Market constituents come from the CRSP 1925 U.S. stock market database. Data is filtered to include common stocks that have a primary listing on either the NYSE, AMEX/NYSE American, or NASDAQ stock exchanges, are issued by U.S.-incorporated corporate issuers, and that trade regular-way (a stock trading under standard settlement terms rather than special conditions) without a special designation. Stocks with multiple share classes are aggregated by PERMCO. Annualized returns are estimated based on quarterly total returns for the CRSP NYSE/NYSE American/NASDAQ/NYSE Arca Value-Weighted Market Index as provided by CRSP.
We map stocks to industries by linking each stock to a four-digit Standard Industrial Classification (SIC) code using CRSP data. We then use the 49 industry groups from the Kenneth R. French Data Library and link each stock’s four-digit SIC code to the corresponding industry in the Kenneth R. French dataset. We attempt to fill any stock-level data-mapping gaps through the following hierarchy: 1) backfill or forward-fill the stock’s SIC code from the adjacent quarter; 2) use a stock’s PERMCO identifier or use the SIC code for PERMCO peers in the same quarter where a stock is missing the SIC code; 3) backfill or forward-fill the SIC code for the PERMCO peer in adjacent quarters where the stock is missing the SIC code; and 4) classify the industry as unknown if the SIC code is still missing. Analysis begins with September 1926 based on data availability. Market constituents come from the CRSP 1925 U.S stock database. Data is filtered to include all common stocks that have a primary listing on either the NYSE, AMEX/NYSE American, or NASDAQ stock exchanges, are issued by U.S.-incorporated corporate issuers, and that trade regular-way without a special designation. Stocks with multiple share classes are aggregated together by PERMCO. Data rounds to the nearest whole percentage point.
1Annualized returns are estimated based on quarterly total returns for the CRSP NYSE/NYSE American/NASDAQ/NYSE Arca Value-Weighted Market Index as provided by CRSP.
2 Inflation-adjusted returns deflate the nominal returns by the quarterly change in the Consumer Price Index for All Urban Consumers: All Items in U.S. City Average (CPIAUCSL), which is obtained from the Federal Reserve Bank of St. Louis (https://fred.stlouisfed.org/series/CPIAUCSL). Sources: Vanguard calculations, using data from CRSP, as of December 31, 2025.
Publication date: August 2026
The information contained in this material may be subject to change without notice and may not represent the views and/or opinions of Vanguard Investments Canada Inc.
Certain statements contained in this material may be considered "forward-looking information" which may be material, involve risks, uncertainties or other assumptions and there is no guarantee that actual results will not differ significantly from those expressed in or implied by these statements. Factors include, but are not limited to, general global financial market conditions, interest and foreign exchange rates, economic and political factors, competition, legal or regulatory changes and catastrophic events. Any predictions, projections, estimates or forecasts should be construed as general investment or market information and no representation is being made that any investor will, or is likely to, achieve returns similar to those mentioned herein.
While the information contained in this material has been compiled from proprietary and non-proprietary sources believed to be reliable, no representation or warranty, express or implied, is made by The Vanguard Group, Inc., its subsidiaries or affiliates, or any other person (collectively, "The Vanguard Group") as to its accuracy, completeness, timeliness or reliability. The Vanguard Group takes no responsibility for any errors and omissions contained herein and accepts no liability whatsoever for any loss arising from any use of, or reliance on, this material.
This material is not a recommendation, offer or solicitation to buy or sell any security, including any security of any investment fund or any other financial instrument. The information contained in this material is not investment advice and is not tailored to the needs or circumstances of any investor, nor does the information constitute business, financial, tax, legal, regulatory, accounting or any other advice.
The information contained in this material may not be specific to the context of the Canadian capital markets and may contain data and analysis specific to non-Canadian markets and products.
The information contained in this material is for informational purposes only and should not be used as the basis of any investment recommendation. Investors should consult a financial, tax and/or other professional advisor for information applicable to their specific situation.
In this material, references to "Vanguard" are provided for convenience only and may refer to, where applicable, only The Vanguard Group, Inc., and/or may include its subsidiaries or affiliates, including Vanguard Investments Canada Inc.