With the SPY at 3567 today, S&P 500 market cap is 29.615 trillion dollars, and Tesla's market cap at $522 is $494.8b, while Tesla's free float is 80.12% of shares issued.

This gives Tesla a pro-forma S&P 500 weight of 494.8/29615*0.8012 = 1.34%.

Few funds have this much TSLA.

According to 13-F filings as of September 30, out of 1,640 institutional investors, 1,540 were underweight and require 132m shares to become equal-weight.

Just 106 funds are overweight, and they only have 108m shares in overweight TSLA shares - not enough to satisfy demand.

There's also about ~20% of the float in mutual funds and non-S&P 500 index funds. These too are underweight TSLA in the aggregate.

Then there's $5.1 trillion in passive index funds, who must buy 125m TSLA shares on or by December 21.

Very large shortfall of TSLA shares.

Finally, there's an unknown amount of TSLA float tied up in options delta-hedging inventory.

Susquehanna and Citadel, the two largest options market makers, reported owning 100 million TSLA shares in early 2020, or 13.2% of the float.

Their stake likely increased significantly.

Currently an estimated 20-25% of the TSLA float is tied up by options delta hedging and for covered calls.

These hedging shares, protecting naked call options, are not available to S&P 500 indexers at any price, so they are effectively removed from circulation.