SpaceX is the sixth-biggest company in the Nasdaq 100 by market value, worth more than $2 trillion. Yet inside the index, it ranks only 19th by weight. The gap comes down to one number, the SpaceX free float, and that number is about to change.
“Free float” is the slice of a company’s shares that anyone can actually buy and sell today. Shares still frozen under a lockup don’t count. A lockup is a promise by insiders and early investors not to sell for a set period after the IPO.
Nasdaq uses this number in an unusual way. To set a company’s weight, it takes the smaller of two figures: the company’s full market value, or three times the value of its free float.
Here is how that plays out. Picture a $2 trillion company with only 10% of its shares trading. That tradable slice is worth $200 billion. Three times that is $600 billion, far below $2 trillion. So the index treats the company as if it were worth $600 billion. That is roughly where SpaceX stood after its IPO, when less than 10% of its shares could trade.
The rule stops biting once the free float reaches one-third. At that point, three times the float equals the whole company, and the discount disappears.
SpaceX is getting close. After lockups expired in August, more than one billion shares were released, lifting the SpaceX free float to nearly 30%. Many feared a wave of selling, but insiders largely held on, and the stock held up.
That is why the next rebalance, taking effect Sept. 21, matters. JPMorgan strategists estimated SpaceX’s weight could rise to 2.25%, forcing about $15.5 billion of buying by funds that track the index. Pro forma data from Nasdaq, circulated late Friday, pointed higher: from roughly 1.28% to about 2.82%. The final number comes later this month. Note that the $15.5 billion figure was built on the smaller 2.25% estimate, so the two numbers shouldn’t be read as a pair.
Why would funds have to buy at all? Index funds don’t pick stocks. Their job is to copy the index, so when a weight changes, they buy or sell to match, whatever the price. About $1.7 trillion tracks the Nasdaq 100. We looked at how this mechanical buying can move a price early in When a Stock Joins an Index.
More SpaceX shares are scheduled to come out of lockup, which could push the weight up again at later rebalances. The S&P 500 is a separate door. Its rules require 12 months of trading history, so SpaceX can’t join until at least mid-2027. The IPO’s ripple effects, which already showed up in bank earnings, are far from finished.
My take: An index doesn’t read the sign on the door. It counts what’s on the shelf.
Not advice. Just how I see it.