The Standard & Poor's 500 Index, or simply the S&P 500, is a market-capitalization-weighted index of 505 large-cap U.S. stocks. The index accounts for 80% of the market value of the U.S. equities market. Because it reflects nearly all of the largest stocks in the U.S., it is often regarded as synonymous with "the market" as a whole. It's the closest there is to a "default" U.S. stock index.

Because it's weighted by market cap, the largest stocks have a big impact on both the long-term performance and daily movement of the index. The 10 biggest stocks make up 26.4% of the index's market value. This means that investors should familiarize themselves with these 10 giant components to understand what drives the broader market.

Below is our analysis of the 10 largest components of the S&P 500. Weighting and market capitalization are as of May 31, 2021, and are courtesy of S&P Dow Jones Indices. Revenue and net income are courtesy of YCharts and are as of June 4, 2021.

1. Apple Inc. (AAPL)

  • Index Weighting: 5.5%
  • Market Cap ($B): 1,966.4
  • Revenue ($B) (4-Quarter Trailing): 325.4
  • Net Income ($B) (4-Quarter Trailing): 76.3
  • Place Change From Last Month: None

Apple is a major producer of hardware and software products, primarily for the consumer market. Its most prominent product is the Apple iPhone brand, but Apple also produces other brands including Mac computers and iPad tablets. It also operates the Apple Music and Apple TV media distribution platforms.

2. Microsoft Corp. (MSFT)

  • Index Weighting: 5.3%
  • Market Cap ($B): 1,883.1
  • Revenue ($B) (4-Quarter Trailing): 160.0
  • Net Income ($B) (4-Quarter Trailing): 56.0
  • Place Change From Last Month: None

Microsoft is a computer hardware and software company that makes products for both personal and enterprise use. A major player in the tech industry for decades, Microsoft is best known for its Windows operating system, the Microsoft Office suite of programs, and the Xbox game system. The company also is a major player in cloud computing services with its cloud platform, Azure.

3. Amazon.com, Inc. (AMZN)

  • Index Weighting: 3.9%
  • Market Cap ($B): 1,379.6
  • Revenue ($B) (4-Quarter Trailing): 419.1
  • Net Income ($B) (4-Quarter Trailing): 26.9
  • Place Change From Last Month: None

Amazon is an online retailer of all kinds of goods but has increasingly diversified its business. It also has a major cloud-computing business known as Amazon Web Services (AWS) and runs the Whole Foods chain of brick-and-mortar grocery stores. On Feb. 2, 2021, Amazon announced that founder and CEO Jeff Bezos will transition to executive chair in Q3 2021, with current AWS CEO Andy Jassy becoming Amazon CEO at that time.

4. Facebook, Inc. (FB)

  • Index Weighting: 2.2%
  • Market Cap ($B): 790.7
  • Revenue ($B) (4-Quarter Trailing): 94.4
  • Net Income ($B) (4-Quarter Trailing): 33.7
  • Place Change From Last Month: None

Facebook runs the largest, most dominant social networking platform in the world. It also owns photo-sharing app Instagram, messenger app WhatsApp, and virtual reality equipment maker Oculus. Facebook rose in the rankings as people spent more time on social media to keep in touch during quarantine.

5. Alphabet Inc. Class A (GOOGL)

  • Index Weighting: 2.0%
  • Market Cap ($B): 708.8
  • Revenue ($B) (4-Quarter Trailing): 196.7
  • Net Income ($B) (4-Quarter Trailing): 51.4
  • Place Change From Last Month: None

Alphabet is the parent company of search-engine giant Google. Among its other products besides the Google search engine, Alphabet runs video-sharing site YouTube. It's notable that the company splits its stock into two main share classes. Google's C shares are nonvoting shares, meaning they do not entitle the holder to participate in proxy votes. The A shares usually trade for slightly more than the C shares and carry voting rights. Each of these shares trades on the S&P 500, and each is large enough, by itself, to make the top 10 list. If the two share classes were counted together, it would place Alphabet fourth on this list and would make up 3.9% of the index. There are also B shares, which have disproportionate voting rights and are only held by Google insiders. The B shares do not trade on the open market.

6. Alphabet Inc. Class C (GOOG)

  • Index Weighting: 2.0%
  • Market Cap ($B): 695.1
  • Revenue ($B) (4-Quarter Trailing): 196.7
  • Net Income ($B) (4-Quarter Trailing): 51.4
  • Place Change From Last Month: None

(See above for company description.)

7. Berkshire Hathaway Inc. (BRK.B)

  • Index Weighting: 1.6%
  • Market Cap ($B): 551.9
  • Revenue ($B) (4-Quarter Trailing): 365.6
  • Net Income ($B) (4-Quarter Trailing): 104.0
  • Place Change From Last Month: Up One

Berkshire Hathaway is a holding company for the various investments CEO Warren Buffett has made over the years. Among its numerous holdings are insurance businesses such as GEICO, large energy and utilities businesses, a major railroad, consumer brands such as ice cream chain Dairy Queen, and manufacturers such as aerospace parts manufacturer Precision Castparts Corp. It also owns an enormous portfolio of equities, which is why Berkshire Hathaway notably fell several places in the rankings. Those equities took a huge hit when stocks dropped during the first quarter, absolutely crushing Berkshire's first-quarter profits and dragging down the company's stock.

8. JPMorgan Chase & Co. (JPM)

  • Index Weighting: 1.4%
  • Market Cap ($B): 501.2
  • Revenue ($B) (4-Quarter Trailing): 123.6
  • Net Income ($B) (4-Quarter Trailing): 40.6
  • Place Change From Last Month: Up One

JPMorgan Chase & Co. is the largest U.S. bank. JPMorgan provides banking services to a wide range of clients. It provides banking services such as mortgage lending, commercial banking services such as business loans, investment banking services such as bond underwriting, and asset and wealth management services.

9. Tesla, Inc. (TSLA)

  • Index Weighting: 1.4%
  • Market Cap ($B): 480.1
  • Revenue ($B) (4-Quarter Trailing): 35.9
  • Net Income ($B) (4-Quarter Trailing): 1.1
  • Place Change From Last Month: Down Two

Tesla is primarily a maker of electric cars. It makes more than 90% of its revenue and virtually all of its profit from its car business, but it also sells solar panels and batteries for homes and businesses. Until recently, Tesla has struggled to make a consistent profit, something that kept it out of the S&P 500. The S&P 500 requires a company to make four consecutive quarters of profit according to generally accepted accounting principles (GAAP).

10. Johnson & Johnson (JNJ)

  • Index Weighting: 1.3%
  • Market Cap ($B): 444.9
  • Revenue ($B) (4-Quarter Trailing): 84.2
  • Net Income ($B) (4-Quarter Trailing): 15.1
  • Place Change From Last Month: None

Johnson & Johnson is a medical and consumer products conglomerate. Its three main businesses are pharmaceuticals (both over the counter and prescription), medical devices, and consumer hygiene and wellness products. The last category includes notable brands such as Band-Aid bandages, Listerine mouthwash, and Neutrogena skin care products. At the end of February 2021, Johnson & Johnson received emergency-use authorization from the Food and Drug Administration (FDA) for a single-dose vaccine for COVID-19.