Amazon, Netflix and Microsoft together this year are responsible for 71 percent of S&P 500 returns and for 78 percent of Nasdaq 100 returns.

The three stocks make up 35 percent, 21 percent and 15 percent of S&P 500 returns, respectively, while making up 41 percent, 21 percent and 15 percent of Nasdaq 100 returns.

Apple also makes up a large portion of both indexes, contributing 12 percent of both S&P 500 and Nasdaq 100 returns, while Alphabet and Facebook contributed 8 percent to each.

In total for 2018, the six stocks make up 98 percent of S&P 500 returns and 105 percent of Nasdaq 100 returns.

The S&P 500 is up 4.4 percent for 2018, while the Nasdaq 100 is up almost 14 percent.

– CNBC’s Robert Hum contributed to this report.