Robinhood, AppLovin Stocks Surge. This Is Driving Them Higher.

The quarterly rebalancing assesses the market value of stocks in the index of the largest companies (Dreamstime)

Shares of Robinhood Markets, the online-trading platform, and AppLovin , an advertising technology company, jumped Monday after they were finally earmarked to join the S&P 500 index after missing out at the last rebalancing.

They will be joined by Emcor Group, a construction and maintenance services company and all will be elevated by Sept. 22—according to S&P Dow Jones Indices, which manages the benchmark index.

Robinhood stock was up 13.5% in early trading and AppLovin was up 12.6% while Emcor was flat. They will replace MarketAxess Holdings, down 0.8%; Caesars Entertainment, down 3.3%; and Enphase Energy, down 3.2%.

The quarterly rebalancing assesses the market value of stocks in the index of the largest companies and typically the smallest drop off, leapfrogged by bigger rivals.

Robinhood Markets has a fully diluted market capitalization of around $93.3 billion and AppLovin’s stands at around $168.6 billion as of Friday’s close, according to FactSet. They had been widely expected to make the cut at the last quarterly rebalancing and the stocks sank when they were not added to the list.

Write to Rupert Steiner at rupert.steiner@barrons.com