Article 7 min

What Is the S&P 500 and How Does It Work?

The S&P 500 is a widely referenced stock market index that reflects the performance of approximately 500 of the largest U.S. companies. While not something investors can buy directly, it serves as a helpful benchmark for understanding how the market is moving overall. The index is composed of firms from across 11 sectors and is designed to give a snapshot of the broader economy's health. For many investors, especially beginners, tracking or investing in funds tied to the S&P 500 offers a way to engage with the stock market with built-in diversification.

Summary

📈 What Is the S&P 500?

The S&P 500 is a market index composed of roughly 500 of the largest publicly traded companies in the United States. These companies represent a wide range of sectors, from technology and health care to utilities and consumer staples. The index itself isn’t a security or product you can buy; instead, it's used as a performance benchmark for the broader stock market. Investors who want to mirror the performance of the S&P 500 can do so by investing in index funds designed to track it. These funds generally aim to match the returns of the S&P 500 as closely as possible, making them a common entry point for those new to investing.

Takeaways:

• The S&P 500 is a stock market index tracking 500 large-cap U.S. companies.

• It cannot be bought directly, but you can invest in funds that replicate its performance.

• It's often used to gauge the overall health of the U.S. economy and stock market.

Key Terms

• Market Index: A grouping of stocks designed to represent a specific segment of the financial market.

• Index Fund: A mutual fund or ETF that aims to replicate the performance of a market index.

• Sector: A distinct subset of the economy, like technology or energy, that companies can be categorized into.

🏢 What Companies Make Up the S&P 500?

The S&P 500 isn’t just a random collection of firms—it includes companies that meet specific criteria. To qualify, a company must have a market capitalization of at least $15.8 billion, be headquartered in the U.S., be structured as a corporation offering common stock, and be listed on an eligible U.S. exchange. Real estate investment trusts (REITs) may also be included if they meet these requirements. Additionally, the company must show profitability both in the most recent quarter and across the last four quarters in aggregate. These filters ensure the index includes only large, stable firms. The list of companies is reviewed and adjusted every quarter to maintain its representative nature.

Takeaways:

• S&P 500 companies must meet strict financial and structural criteria to be included.

• The list is updated quarterly to reflect changes in the market.

• Inclusion typically signals a company’s financial stability and size.

Key Terms

• Market Capitalization: The total market value of a company’s outstanding shares.

• REIT: A company that owns or operates income-producing real estate.

• Common Stock: A form of corporate equity ownership.

💹 Can You Invest in the S&P 500?

Although the S&P 500 itself is not a security you can purchase, you can invest in funds that mirror its makeup. These are often referred to as S&P 500 index funds. Popular examples include Vanguard 500 Index Investor Shares (VFINX), Fidelity 500 Index Fund (FXAIX), and Schwab S&P 500 Index Fund (SWPPX). Each of these funds is designed to replicate the performance of the S&P 500 by holding shares in the same companies with matching weightings. Investors can access these funds through brokerage accounts, and they are often considered a core component of long-term, diversified portfolios.

Takeaways:

• You can't buy the S&P 500 directly, but you can invest in index funds that track it.

• These funds are a common way to gain broad market exposure.

• They are available through most online brokerage platforms.

Key Terms

• Index Fund: A portfolio of stocks designed to match the composition of a market index.

• Brokerage Account: An investment account used to buy and sell financial securities.

• ETF: Exchange-Traded Fund, a type of index fund that trades like a stock.

📊 How Is the S&P 500 Calculated?

The S&P 500’s value is determined using the market capitalizations of its component companies. This is calculated by multiplying each company's share price by the number of outstanding shares. However, only shares available to the public are factored in, known as the "float." The index is weighted, meaning larger companies influence the index more heavily than smaller ones. The total weighted market cap is then divided by a proprietary divisor to arrive at the index number displayed on financial news tickers. As company stock prices fluctuate, the index value adjusts in real-time to reflect those changes.

Takeaways:

• Market capitalization determines a company’s weight in the index.

• The index updates continuously as share prices change.

• A proprietary divisor is used to normalize the index value.

Key Terms

• Float: The number of shares available for public trading.

• Weighting: The influence a single company has on an index based on its size.

• Divisor: A constant used in the calculation of an index’s value.

📆 Historical Returns of the S&P 500

Over nearly a century, the S&P 500 has returned an average of about 10% annually when dividends are reinvested. This figure is not adjusted for inflation and can vary significantly year to year. For example, in 2008, the index dropped 37%, but it rebounded 26% in 2009. This fluctuation demonstrates the importance of taking a long-term perspective when investing in the S&P 500. Returns can differ greatly in the short term, and patience is often required to realize average returns over time.

Takeaways:

• The long-term average return is about 10% per year.

• Annual returns vary and can include significant losses or gains.

• A long-term mindset is essential for index fund investors.

Key Terms

• Dividend: A portion of a company’s earnings distributed to shareholders.

• Volatility: The degree of variation in investment prices over time.

• Inflation: The rate at which the general level of prices for goods and services rises.

🏛️ How Does the S&P 500 Differ From the Dow?

The S&P 500 and the Dow Jones Industrial Average (Dow) are both major market indexes, but they differ in structure and purpose. The Dow includes only 30 companies and weights them by share price, not market cap. This means a company with a higher stock price, even if it’s smaller in size, can have more influence on the index. The Dow focuses on nine sectors, while the S&P 500 represents 11. While both indexes track large, influential companies, the S&P 500 offers broader market representation, making it a more comprehensive reflection of the economy as a whole.

Takeaways:

• The Dow includes only 30 companies, compared to the S&P 500’s 500.

• The Dow is weighted by stock price, not market cap.

• The S&P 500 spans more sectors and is broader in scope.

Key Terms

• Dow Divisor: The constant used to calculate the Dow Jones index value.

• Share Price: The cost of a single share of a company’s stock.

• Sector Allocation: The distribution of companies in an index across different economic sectors.

Conclusion

The S&P 500 serves as a valuable indicator of U.S. stock market health and offers a diversified snapshot of corporate performance across multiple sectors. While not something you can invest in directly, index funds that track the S&P 500 provide a practical way for investors to tap into the broader market. Whether you're just starting out or looking to build long-term wealth, understanding how the index functions can be a helpful step in shaping your investment strategy.