In late 2025, the top 10 companies in the S&P 500 made up more than 40% of the index's total value

Why some say the S&P 500 has effectively become an AI fund

The S&P 500 is a market-cap-weighted index, which means companies with larger market capitalizations have a larger impact on the index's overall performance. Many of the top companies in the index are currently tech companies—including Nvidia, Microsoft, Alphabet, and Apple—that all have large investments in artificial intelligence. As a result, some analysts are concerned that the index is overly exposed to risky AI investments.

Before the S&P 500 launched in 1957, Standard and Poor's had a daily index with just 90 companies

Unlike previous indexes from S&P, the S&P 500 could be computed in real time using computer technology that tracked stock tickers across stock exchanges. This innovation is partly what led to 500 companies being listed on the index, a huge increase from the 90 companies in S&P's flagship index when the company had to do all the analysis by hand.

A 'large-cap' company has a market capitalization of more than $10B

The S&P 500 is primarily composed of large-cap companies. The idea is that the index provides a big-picture view of the economy by assessing the performance of many of the largest public companies across different industries. The median market capitalization of companies listed on the S&P 500 is around $40B.

The S&P 500 is composed of 500 companies, but has more than 500 total listings

Since some large companies have dual-class stock structures (like Alphabet and Fox Corporation), there are multiple listings on the S&P 500 for the same company. S&P Global has banned and then reversed bans on companies with dual-class structures multiple times since first allowing dual-class stocks in 2014.

The S&P 500, managed by the same company, is another major stock index

Also run by S&P Dow Jones Indices, the S&P 500 tracks 500 large US firms using market-value weighting. Many analysts view it as a more accurate gauge of the American economy.

S&P Global, the company that makes the S&P 500, is listed on the S&P 500

When the S&P 500 index was released in 1957, it was helpful for investors, but not necessarily profitable. S&P Global now makes more than $1B a year just from selling its index data. Alongside its other services, like credit ratings, S&P Global makes more than $14B a year.

Listen to the methods and strategy of the secretive S&P 500 selection committee

Stocks are added to the S&P 500 by a secret selection committee that meets regularly to assess which companies can remain in the index, which companies need to be added, and which companies no longer meet the criteria. The members of the committee used to be public, but S&P Global decided to keep its members confidential after companies sent packages, letters, and gifts to try to make it into the index.

The S&P 500 selection committee has strict rules around adding a company to the index

While the decision to add a company to the index is ultimately up to the selection committee, any prospective company has to meet some criteria to be considered. To join, the company must have been profitable for the last four quarters, must have a market capitalization exceeding $22.7B, and meet certain requirements around tradeable stock availability (or float).

Investors rely on the S&P 500 as a benchmark for the state of the economy

Since the index represents a broad range of diverse industries, it's become a proxy for the market itself and a common benchmark for investors to compare returns and performance patterns against. Generally speaking, when someone says a stock is under- or out-performing the market, that actually means under- or out-performing the S&P 500. The S&P 500 is exchange-agnostic, and includes companies listed on both the NYSE and Nasdaq.

Some argue that the S&P 500 is actually an actively managed index

Some critics of the S&P 500's selection process argue that human involvement makes it an actively managed index. S&P Global maintains that while a human selects the stocks in the index, those decisions are not made with the intent of maximizing performance, but rather, to provide a snapshot of the largest companies across different industries.

The Dow Jones Industrial Average vs. the S&P 500: Which one is a better representation of the economy?

The Dow and S&P 500 are both indexes meant to provide a broad representation of the economy. The Dow has 30 companies and is weighted by share price, while the S&P 500 has 500 different companies weighted by market capitalization. Since the indexes are so different, investors don't always agree on which index is a better representation of the economy—though the two move in the same direction more than 90% of the time.

A stock index is a group of companies clustered together, often providing a condensed snapshot of a market segment.

Read about the evolution of the S&P 500 and its recession recovery

Since the S&P 500 is considered a bellwether index (meaning it represents the health of the US economy), its value is important for investors in both bull and bear markets. The S&P 500 has been impacted by recessions and downturns, from the 1970s oil crisis to the dot-com crash of the early 2000s.

Many of the top companies in the US by market cap began as tech startups

Combined, the top seven companies by market cap in the US as of December 2024—Apple, Nvidia, Microsoft, Alphabet, Amazon, Meta, and Tesla—were worth more than $16T at the time.

Critics argue the Dow no longer reflects the modern economy

With only 30 companies and a price-weighted formula, skeptics say the DJIA underrepresents vast sectors of the market. They claim it is outdated, though its close correlation with the broader S&P 500 keeps it relevant.

See a timeline of S&P Global's history—the company behind the S&P 500

From the 1941 merger of Standard Statistics and Poor's Publishing to the creation of the S&P 500 in 1957, the company that created the famous index has long been a leader in financial intelligence.

Watch how the S&P 500 is actually calculated

After accounting for each company's float-adjusted market capitalization (a metric that combines the price of a company's stock, the total number of shares, and the stock's float, which means how many shares are actually available), the S&P 500 formula uses a divisor to create the index number. However, what the divisor is and what it represents are secrets.

Millions of Americans will be invested in SpaceX because of the fast-tracked process to list SpaceX on the Nasdaq 100, and, subsequently, the index funds that track it.

The S&P 500 yields a roughly 10.5% average annual return

Tthe factors that go into that calculation are multifaceted—from how inflation impacts it to the stocks themselves. During periods of high inflation, stock performance can be stunted by investor concerns, for instance. The average return also varies based on whether dividends are included.

Visualizing decades of stock market performance

Stock markets and the indexes that track their biggest companies tend to ebb and flow, with long growth periods punctuated by shorter recessions. Track the 60-year history of one of the most common stock market indexes, the S&P 500, with this data visualization. The chart highlights the long-term durability of markets despite appearance of short-term volatility.

The Nasdaq's 'Magnificent 7' have an outsized impact on the Nasdaq 100's performance

These seven companies are Alphabet, Amazon, Apple, Meta, Microsoft, Nvidia, and Tesla. They're often responsible for over 40% of the Nasdaq 100 index's gains, but the exact percentage varies from year to year.

The world's 50 most valuable private companies

While public companies typically have the highest valuations, private companies get close. This list breaks down the top 50 as of 2025, with SpaceX at the top with a value of $350B, followed by ByteDance. Over three-fifths of the list are located in the US, with eight in China.

Some institutional investors are growing wary of private equity, as certain investments underperform traditional market indices

Private equity often attracts investors who can afford to tie up capital for long periods of time in exchange for higher returns than traditional investments. For many years, private equity at least tracked with the S&P 500 in terms of returns to investors, but in 2024 and 2025, it underperformed and posted declining returns.

The wealthiest Americans own the vast majority of the stock market

Recent data from the Federal Reserve shows that the richest people in America own 93% of all the country's stock—the highest level ever recorded. Meanwhile, the bottom 50% of Americans held just 1% of all stocks.

See how the S&P 500 performed throughout the first 100 days of each modern presidency.

The 'Big Three' asset managers—Vanguard, State Street, and BlackRock—collectively manage more than $30T in assets and are the largest shareholders in roughly 88% of all the companies listed on the S&P 500.

Worth more than $14T, Silicon Valley may be getting too expensive for future founders.

71% of equity investments in Q1 2025 went to AI companies

That's up from just 14% in 2020, according to JPMorgan, which recently conducted an analysis of venture capital investment trends in the US.

The Dow now tracks 30 major US companies across various industries

Since 1928, the DJIA has included 30 firms. Today's group spans technology, healthcare, and finance—with Apple, Microsoft, JPMorgan Chase, Pfizer, and Coca-Cola among its most recognized components.

Even iconic companies can get dropped from the Dow

The Dow’s lineup evolves as the economy changes. General Electric, part of the original 1896 index, was removed in 2018, after 122 years. ExxonMobil, once the world’s largest company, was replaced by Salesforce in 2020.

More than 650 companies went public in the US in 1996

As the dot-com bubble reached its peak, most dot-com companies went public with little proof of being profitable and were often overvalued. In 1999, the Nasdaq's price-to-earnings ratio (a tool used to determine a stock's value that divides its price by earnings) hit 90.2, signaling that many companies were operating at a net loss. Startups promised investors that more time and money would help scale their businesses and become profitable.

The S&P 500 has an average intra-year drawdown of -16%

In a given year, the value of the S&P 500 can significantly fluctuate. An intra-year drawdown is the most significant difference between the index's peak and lowest point.

The top 100 companies in Silicon Valley

Silicon Valley has pumped out some of the biggest companies in the world, including Apple, Meta, and Google. Thousands of companies operate in the area, ranging from valuations in the trillions to startups only worth thousands.

The number of publicly traded companies has decreased significantly

The stock market hit a peak in 1996, when more than 7,000 companies were publicly traded. But in 2024, there were nearly half that many publicly traded companies.

The dot-com boom sent tech stocks soaring before a historic collapse

A look at the dot-com bubble, when investors poured money into unproven internet startups, driving the Nasdaq to dizzying heights before it crashed by more than 80% after 2000, showing how new technologies can detach markets from reality.

US IPO issuance—the total dollar amount of new stock sold to the public via IPOs—hit a record high in 2026.

Biotech ETFs allow investors to gain exposure to multiple promising companies in the industry

Biotech ETFs offer a diversified alternative to purchasing an individual biotech stock and gambling on whether an individual company’s clinical trial yields the next blockbuster cancer treatment or an absolute flop. This list of the top biotech ETFs in 2025 can help you learn more about them.

The Dow’s price-weighted formula makes stock price matter more than size

Unlike most indices, which weigh companies by market value, the DJIA is price-weighted—meaning higher-priced stocks have more influence on its movements. As a result, a company’s share price matters more than its overall size.

See the top 100 ETFs by trading volume

This list grabs the top 100 by trading volume, or the average number of shares that have traded hands over a 3-month period. Top of the list is a semiconductor-focused fund from Direxion, followed by other tech-centric offerings.

The SPDR S&P 500 ETF is one of the most highly traded funds on the market

State Street, a popular ETF issuer, is responsible for the SPDR S&P 500 ETF. This fund trades under the SPY ticker, and State Street maintains a web page with key facts and figures on SPY. For instance, its expense ratio is 0.0945%, or $9.45 on an initial $10K investment.

Vanguard Group founder Jack Bogle created the first index fund, the Vanguard 500, in 1976—but the fund didn't take off until the 1990s.

Read about the 'gatekeeper' of the stock market, former index chair at S&P Global

David Blitzer, the former index chair at S&P Global, earned the nickname "gatekeeper" of the stock market after helping decide which companies made it into the S&P 500 for 24 years. Blitzer became a legend in the world of indexing and has a reputation for being even-tempered and always wearing a bow tie.

Nearly half of billionaires planned to increase exposure to direct private equity investments in 2026.

Just because a big name company is going public doesn’t guarantee a successful stock

A reporter dove into how highly anticipated IPOs can still be risky, and why retail investors should be wary of investing right away.

Visualize the world's top 50 private equity firms in 2025 by capital raised.

The Nasdaq 100 index tracks the exchange's 100 largest non-financial companies

This index was created in 1985, over a decade after the Nasdaq first launched. The companies on the index must meet certain criteria, including having a minimum average daily trading value of $5M.

Read how Vanguard's founder used the S&P 500 to revolutionize retail investing

John Bogle, the founder of The Vanguard Group, created a fund that tracked the S&P 500 in 1976. That fund created an unprecedented opportunity for individual retail investors, brought down fees across the board, and popularized the belief that passive, low-cost index fund investments would outperform actively managed portfolios long-term.

See Bloomberg's continuously updated Billionaire Index

This ranking, updated daily, shows a running tally of the world's 500 richest people. Tesla and SpaceX CEO Elon Musk has largely been atop the list, with a net worth of around $723B as of June 2026. Values fluctuate significantly as much of the wealth is tied to equity in companies. (Some users may experience a paywall.)

Visualize the world's top 20 billionaires in 2026

This data visualization shows the 20 wealthiest people in the world as of January 2026. Topping the list with a net worth of more than $713B is Elon Musk, trailed by Larry Page ($258B), Jeff Bezos ($251B), and Larry Ellison ($243B).

Explore a tool that shows how much stake large asset managers, including BlackRock, hold in public companies.