What will happen when Tesla (NASDAQ:TSLA) joins the S&P 500 today?

On the ASX this week, much is being made of S&P Global Inc’s quarterly index rebalancing that takes place today. Indexes work by constantly updating their inclusions and weightings to reflect the status of the broader market of the time. Take the S&P/ASX 200 Index (ASX: XJO) for instance.

This index’s purpose is to measure the performance of the 200 largest companies in the ASX. These 200 companies obviously change over time, so the index needs to be on top of that for it to work effectively. Hence why it is adjusted and rebalanced every quarter. Growing companies might join the index, replacing those that might be out of favour or stagnating.

As an example, this week sees Afterpay Ltd (ASX: APT) join both the ASX 20 and the…