Shares of Tesla will join the S&P 500 on Dec. 21, the biggest-ever single-stock addition to the index, and that is when funds indexed to the S&P essentially start buying. That makes this week a big deal for the stock—for two reasons.
For starters, this is the final week traders have to position themselves ahead of index buying. That might drive higher-than-average volatility.
Second, Friday’s closing price will set the weighting of $Tesla (TSLA.US)$