Who are the stock market heavyweights?

FILE - In this Thursday, May 9, 2013 file photo, people walk near the Apple store in Santa Monica, Calif. Even after its recent slump, Apple's market value is still two thirds bigger than Microsoft, the next biggest publicly-traded company in the U.S. That means that when Apple moves, so does the market. (AP Photo/Reed Saxon, File) FILE - In this Thursday, May 9, 2013 file photo, people walk near the Apple store in Santa Monica, Calif. Even after its recent slump, Apple's market value is still two thirds bigger than Microsoft, the next biggest publicly-traded company in the U.S. That means that when Apple moves, so does the market. (AP Photo/Reed Saxon, File)

By Associated Press August 5, 2015 3 min read

NEW YORK (AP) – At $660 billion, Apple is the stock market’s heavyweight.

Like a handful of other “big cap” companies such as Microsoft and Exxon Mobil, the iPhone maker’s market value means that when its shares move, so can the market. And these are the companies that influence your stock portfolio.

“The combination of Apple’s size and price moves, results in an enormous impact on indices,” says Howard Silverblatt, a senior index analyst for S&P Dow Jones Indices.

Lately, Apple’s influence has been a drag.

Since closing at a record $133 on February 23, Apple has slumped to $116.53, wiping more than $120 billion off the value of its stock. Between then and Tuesday’s close, the Standard & Poor’s 500, the most widely-tracked stock index, was down 0.8 percent.