Tesla, the Largest-Cap Stock Ever to Enter S&P 500: A Buy Signal or a Bubble?

Key Points

  • Tesla is entering the S&P 500 with a stupendously high valuation and will likely be ranked sixth in the index. Traditional cap-weighted indices, such as the S&P 500, are structured to buy high and sell low—and Tesla is a prime example of this maxim.

  • The eightfold increase in Tesla’s share price since its March low meets our two-part definition of a bubble: 1) implausible assumptions are needed to justify its valuation, and 2) buyer interest is based on a great narrative rather than being supported by a conventional valuation model.

  • Our research shows that a continuation of Tesla’s 2020 share-price performance is vulnerable on two additional fronts: 1) as a top-dog stock (top 10 market-cap stocks), the odds are against its remaining a top-dog stock, and 2) as an addition to the S&P 500, history indicates it is likely to underperform the market (S&P 500) in the year after entry.

  • Our research also demonstrates that Apartment Investment and Management, the stock removed from the S&P 500 to make way for Tesla, is likely to outperform the index over the next year by as much as 20%, based on the average outperformance of all deletions from the index in the 31-year period from October 1987 through December 2017.

Rob Arnott is the corresponding author.

On November 16, S&P Dow Jones Indices announced that Tesla will (finally) join the prestigious S&P 500 Index on December 21. From the beginning of 2020 to the announcement date, Tesla’s share price rose 400% from $83.67 to $408.09. Most of that run-up occurred after the media began speculating in March about Tesla’s likely addition to the index. From the announcement date through December 7, Tesla’s share price rose another 49% to $608.32. That’s an eightfold increase from its March low.