Stocks within many indexes are weighted by market cap.
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A companyâs market capitalizationâor total outstanding share valueâmight not seem important when you buy the smartphone, cereal, or car the company manufactures. But when you buy shares, market cap isnât just a ranking system for stocks. Itâs like having a playbook that tells you how a stock might behave.
An ocean freighter loaded with heavy cargo doesnât zip through the waves like a speedboat on your local lake. Stocks also behave differently based on size. Traditionally, the biggest behemoths on Wall Street often cruise along more slowly and steadily, while the smallest companies are primed for speed and maneuverability. Thatâs why many analysts say you should consider a mix of different market caps in your portfolio for proper diversification.
Key Points
- Market capitalization is the number of outstanding shares of a company multiplied by its stock price.
- Many major market indexes are organized by large-cap, mid-cap, and small-cap companies.
- Market cap can influence how a stock behaves and influence your investment strategy.
You encounter market capitalization every time you check the major indexes. The Dow Jones Industrial Average (DJIA) andS&P 500 (SPX), for example, are packed with some of the largest companies. The Russell 2000 (RUT) tracks 2,000 âsmall-capâ companies.
Some monster names on Wall Street, such as Apple (AAPL) and Microsoft (MSFT), have sometimes boasted market caps of $2 trillion or more. But many stocks donât even reach $1 billion on the market cap scale. That means the biggest stocks are worth more than 2,000 times the smallest, kind of like comparing the Queen Elizabeth luxury liner to a kayak.
How market cap is determined
What is market capitalization, exactly? Itâs calculated with simple multiplication:
- Stock price (X) multiplied by the number of shares outstanding (Y) = market capitalization (XY).
Companies issue shares, and the market decides every day at what price those shares should trade. The outcome is the total share value, or market cap, of the company.
Bitcoin and other cryptocurrencies also can be valued by market cap. Hereâs how crypto market cap is calculated:
- Current price (X) multiplied by the number of coins in circulation (Y) = market capitalization (XY)
Market capitalization and stock indexes
Stock indexes tend to focus on specific stock sizes, and the value of an index is often calculated based on company market caps. For instance, to be added to the S&P 500, which covers approximately 80% of U.S. market capitalization, a stock must have a market cap of $14.6 billion or greater. That figure is reviewed quarterly and may be adjusted. It also doesnât apply to companies already in the index, so a company could potentially remain in the S&P 500 if its cap falls below $14.6 billion.
The SPX is a âmarket-cap-weightedâ index, meaning stocks with larger market caps have a bigger impact on the indexâs performance. The idea behind cap-weighted index calculation is that the highest-valued stocks should have a bigger impact on index performance. So, a $2 trillion company has far more impact on S&P 500 performance than, say, a $15 billion company.
Good to Know
At one point in 2021, five major technology companies (Apple, Amazon, Facebook parent Meta, Microsoft, and Google parent Alphabet) made up nearly 23% of the S&P 500âs value. The other 495 stocks, combined, accounted for the remaining 77%. So when the SPX makes, say, a 2% move, itâs important to check the top few stocks and see how they performed. That often tells most of the story. It also means there are days when hundreds of S&P 500 stocks fall, but the index rises anyway (and vice versa).
The DJIA, on the other hand, is a âprice-weightedâ index of 30 large-cap U.S. stocks. The price-weighted nature of the index means price changes in its highest-priced stocks have a greater impact on the index level than price changes in the lower-priced stocks, regardless of company size. That makes it a bit of a relic and perhaps a less reliable indicator of overall market performance. Many market experts recommend following the SPX more closely for a quick snapshot of overall stock performance.
FTSE Russell indexesâa subsidiary of London Stock Exchange Group, which manages the RUT and several other indexesâperforms an annual âreconstitution,â in part to determine where companies fit along the capitalization spectrum. This way, when investors buy an index fund based on the Russell 2000, they can be sure no stocks in the fund have outgrown their small-cap status.
Notes on market cap behavior
Although there are no firm and fast rules for how a stock behaves based on market cap, there is some common wisdom in the markets about how large-caps tend to move relative to small-caps, based on outside factors such as recessions and the strength of the dollar. Here are a few to keep in mind:
- Dividends and growth stocks. Until recently, many investors saw large-cap stocks as steady performers that typically paid dividends, delivered predictable earnings, and were viewed as âcash cowsâ rather than high-growth flyers. That changed with companies like Apple and Microsoft, which continue to post huge growth numbers many decades after becoming publicly held companies. Plus, they pay dividends.
- Old-line large-caps. Investors seeking dividend income and slow but steady earnings still often choose large-cap stocks that have been around for decades. Many of the big industrial, materials, and consumer staples companies fit into this category. Think Caterpillar (CAT), Dow (DOW), and Coca-Cola (KO), for example.
- Small-caps and the domestic economy. Small-caps, and to some extent mid-caps, tend to do more of their business domestically, meaning they often perform best when the U.S. economy accelerates. When the U.S. economy flags, small-cap companies, with their heavier domestic exposure, can sometimes be the first stocks to lose ground. Sometimes their revival can signal the final stage of a recession.
- The U.S. dollar. Large-cap companies often do a heavier percentage of their business overseas. They may benefit when the dollar is weak, because a weak dollar tends to give overseas economies a boost. A strong dollar, on the other hand, makes products of large, multinational companies more expensive to overseas customers and can weigh on large-cap earnings.
When the dollar is strong, small-cap companies sometimes benefit from their domestic exposure. A strong dollar can make it less expensive for U.S. companies to buy products from overseas, helping their margins.
Knowing a stockâs market capitalization can provide a sense of how it might behave under different economic circumstances, and also helps you understand the composition and performance of major market indexes.
Investors might want to divide their portfolio among stocks of different market capitalizations, or they could risk losing too much ground when large-caps or small-caps sag.
This article was most recently revised and updated by Dan RosenbergThis article was most recently revised and updated by Doug Ashburn
