What is Standard and Poor's 500 (S&P 500) Index?

The Standard and Poor's 500, or simply the S&P 500, is a stock market index tracking the stock performance of 500 largest companies listed on stock exchanges in the United States. It is one of the most commonly followed equity indices and includes approximately 80% of the total market capitalization of U.S. public companies.

The name, Standard and Poor, came from the merger of Poor's Publishing and Standard Statistics Company, forming Standard & Poor's in 1941.

Components of S&P 500 index are maintained by S&P Dow Jones Indices, jointly owned by S&P Global, the CME Group, and News Corp. A committee meets regularly to decide if any components need to be replace. As of Feb 1, 2025, S&P 500 actually contains 503 common stocks issued by 500 companies.

The value of S&P 500 index is calculated using the free-float weight/capitalization-weighted method, which can be described as:

Index Value = ∑ (Stock Weight) * (Stock Price)

where: 
  Stock Weight = (Free Float Market Cap) / ∑ (Free Float Market Cap)
  Free Float Market Cap = (Float Factor) * (Market Cap)
  Float Factor = (Publicly Traded Shares) / (Total Shares)

Since weights on individual components are relatively stable, the index value can be calculated instantly as individual component stock prices change on stock markets.

The exact weights of individual components within the S&P 500 are not publicly disclosed by S&P Global. You need to pay a huge license fee to get them. But you can get a proximate version from the oldest S&P 500 ETF, SPY. Here are the weights of top 10 components in the S&P 500, as of Jan 31, 2023:

Stock Name                    Ticker  Weight     Value
----------------------------  ------  ------   -------
Apple Inc.                    AAPL     6.98%    421.63
Microsoft Corp                MSFT     6.00%    362.43
Nvidia Corp                   NVDA     5.94%    358.81
Amazon.com Inc                AMZN     4.27%    257.93
Meta Platforms, Inc. Class A  META     2.91%    175.78
Alphabet Inc. Class A         GOOGL    2.28%    137.72
Tesla, Inc.                   TSLA     2.17%    131.08
Broadcom Inc.                 AVGO     1.96%    118.39
Alphabet Inc. Class C         GOOG     1.87%    112.96
Berkshire Hathaway Class B    BRK.B    1.68%    101.48
...
Others                                63.94%  3,862.31
Total                                100.00%  6,040.53

Some historical values of the S&P 500 index are listed below:

2024-12-31  5,881.63
2023-12-29  4,769.83
2022-12-30  3,839.50
2021-12-31  4,766.18
2020-12-31  3,756.07
2019-12-31  3,230.78
2018-12-31  2,506.85
2017-12-29  2,673.61
2016-12-30  2,238.83
2015-12-31  2,043.94

For the current value of the S&P 500 index, see the ^GSPC quote chart on Yahoo Finance.

⇒ SNP: ^GSPC - Standard and Poor's 500

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