Shares of the electric automaker — which have increased fivefold since the beginning of the year — were down more than 15 percent Tuesday morning as investors reacted to the company not being added to the S&P 500 on Friday.

Tesla had been widely expected to be added to the index after the company reached its fourth consecutive profitable quarter. An addition to the S&P would have forced a slew of investment funds that duplicate the S&P’s holdings to buy an estimated $40 billion worth of Tesla shares to avoid errors tracking the index’s performance.

“Clearly the S&P decision is weighing heavily on the stock,” CFRA Research analyst Garrett Nelson told The Post. “The news was really a surprise.”

CFRA on Friday changed its Tesla rating from “sell” to “buy,” with Nelson saying that inclusion could still be around the corner.

“They might not want to telegraph their moves because it’s going to cause such a seismic change in the overall holdings of the S&P 500,” Nelson said. “But we still think there’s a deepend chance they do this in the coming weeks.”

Tesla investors were also reacting to the news that the company’s largest outside shareholder, Baillie Gifford, last week reduced its stake in the company from 6.3 percent to just under 5, as well as to the company’s announced plan to raise $5 billion by selling stock.

Tesla shares were down 15.6 percent Tuesday morning, at $352.99 per share.