SpaceX's weight in the Nasdaq 100 is expected to rise after the index's quarterly rebalance later this month, potentially triggering more than $12 billion in passive net buying. According to Sina Finance, the adjustment will be announced after Friday's close and take effect on September 21.

The company currently has a 1.25% weight in the Nasdaq 100, ranking 19th, even though its market value exceeds $2 trillion and ranks sixth among index constituents. A report released Tuesday by JPMorgan Securities strategist Min Moon and others said SpaceX's weight could reach 1.51% after the rebalance, which would lead index funds and ETFs to buy about $12.4 billion of SpaceX shares.

Nasdaq calculates constituent weights based on market capitalization, but uses the lower of total shares outstanding or three times free-float shares. More than 1 billion shares have now been unlocked, lifting SpaceX's free-float ratio from less than 10% shortly after the IPO to nearly 30%.

Nasdaq data showed about $1.7 trillion in assets tracked the Nasdaq 100 at the end of the second quarter, including the Invesco QQQ Trust Series 1 ETF, widely known by its ticker QQQ. SpaceX shares fell about 1% in early Tuesday trading.

River Wealth Advisors CEO Ed O'Gorman said passive buying of this kind can move market prices, while Interactive Brokers chief strategist Steve Sosnick said newly unlocked shares could be sold into the expected buying, or index-fund demand could push the stock higher.