The table below shows the historical total market capitalization of the S&P 500 index. The total market cap is the sum of the market values of the individual companies part of the index. The table includes also the float adjusted market cap that considers the free-float market value of the companies. The current (12/31/2019) market cap of the S&P 500 is $28,125,589.1 million and the public float adjusted market value is $26,759,679.8 million.

[S&P 500] – Total & Float Adjusted Market Cap (USD, M)

Purchase a dataset that lists the monthly total market value of S&P 500 index since 3/31/1979, including float adjusted cap since 9/30/2006.

For key historical data of the index companies, purchase the S&P 500 Researcher Dataset by Siblis Research which provides share prices, earnings, revenues, outstanding shares, market caps, enterprise values, P/E & P/B ratios and EV/EBITDA multiples of all current & past S&P 500 companies since 3/31/1979. The dataset provides also adjusted share prices (total returns) which allows you to examine the performance of the companies before/during/after a company was part of the index. Download a sample dataset from here.

Total & Float Adjusted Market Cap

Since 2005, S&P 500 has been float weighted. When the individual market cap is calculated for a company part of the index, only the outstanding shares that can be freely traded without any restrictions are taken account. Not all outstanding shares of a company are available for common investors to trade, for example shares held by individuals with access to insider information are under special regulation. The float adjusted value of S&P 500 index is around one trillion dollars smaller the unadjusted total cap.

The ups and downs of S&P 500

The market cap of the index has rose from 172 billion in March 1957 to 925 billion in Dec 1980 and finally to 19 trillion of today. So putting your money on US equities has been quite profitable on the long term.

Between 1970 and 2015, the market value of S&P 500 index has increased around 10% on an annual basis. The growth has of course not been steady but highly cyclical. The fastest growth period was between 1995 and 1999 when the market cap of S&P 500 quadrupled from $3 trillion to $12 trillion. The extremely fast increase in stock values was halted by the dot-com boom and during the next two years the index value decreased almost by half. In the beginning of 2000s, the share values reached again their pre-bust values of 1999 but then again were struck down by another crisis, the 2008 financial crisis. In February 2009, the market cap of the index was just $6.6 trillion, lowest since 1997. The values recovered rapidly and stocks rose for the next five years. On July 2013, S&P 500 soared past $15 trillion in value. However, the worries about China brought down the market during the end of 2015 and the long period of growth was again over.

S&P 500 market cap to GDP ratio: relationship with stock returns?

The graph below shows both the historical cap-to-GDP ratios and the 3-year forward returns of S&P 500. The 3-year forward return means the return that an investor will accumulate if investing to the index during a certain day. For example, in 1/31/2012 the forward return was 52.01% which means that if you invested to some S&P 500 index fund on this day, your profit after 3-years was 52.01%. Note that the scale for the return is inverted.

There is a strong negative correlation between the ratio and stock market returns. Between 2001 and 2002, the market cap-to-GDP ratio was sharply decreasing when the aftermath of dot-com boom and 9/11 terrorist attacks were wiping out market value of companies around the world. Investors who put their money on S&P 500 on 1/1/2001 generated a negative 3-year return of 17%. But as the ratio was plummeting, the future returns started to rise. In 1/1/2013, the future return was +50%.

At the beginning of 2013, the market values of companies started to increase and the ratio quickly rose from 70& to 90%. The ratio kept slowly increasing between 2004 and 2007 but it was impossible to predict the destruction of financial crisis from the ratio. Prior to the crisis, the negative correlation between cap-to-GDP and future returns vanished. The stock market crashed in 2008 and the ratio sunk. Investors who put their savings to S&P 500 shares at the end of February 2009 generated an impressive 3-year return of 86%.

Since 2008, the future return has quite closely followed the cap-to-GDP ratio. For the past six years, the ratio has been steadily rising with only two small dips during 2010 and 2011. The growth has now halted and it might be that a peak has been achieved. If the connection between stock returns and cap-to-GDP stays the same, this would suggest that stock market is overvalued and investors should expect poor yields for equity.

S&P 100 and S&P 500 indexes

The S&P 500 consists of the 500 largest US companies whose stocks are listed on the NYSE or NASDAQ. The index is managed by S&P Dow Jones Indices. It is one of the most followed stock indexes in the world and the performance of the index is commonly used as a representation of the whole US stock market. The common tickers for the index are $SPX, INX and ^GSPC. S&P 100 is a subset of the S&P 500 and includes the leading 100 shares of the mother index. A common symbol for the sub-index is OEX.