Short sellers targeting SpaceX (Nasdaq: SPCX) are sitting on an estimated $8.7 billion in paper profit as of July 16, 2026, with the stock having slipped below its June 12 IPO price of $160.95, according to Ortex data cited by Reuters. SPCX closed at $135.27 on July 15, per WSJ market data — roughly 16% below the offering price.

The short interest trajectory has been steep and fast. On June 23, CNBC reported roughly 40 million shares sold short, about 5% to 7% of the publicly available float. By the time of Yahoo Finance's July 2 report, short interest had climbed to approximately 83 million shares, or 13% of free float. The Wall Street Journal recorded 111.3 million shares short as of June 30. Reuters reported 196 million shares short — about 31% of free float — on July 1. By July 16, Invezz reported short interest at 181 million shares, making SPCX Wall Street's most shorted new stock. Ortex, whose real-time data may differ from exchange-settlement figures, pegged short interest as a percentage of free float at 26.07%, with a short interest value of $23.18 billion.

The cost of carrying a short position in SPCX has been remarkably low. Borrowing fees run just 1–3% annualized, according to S3 Partners. Reuters reported on June 23 that short sellers were finding it easier to borrow SpaceX shares — a signal that lendable supply was expanding as the post-IPO settlement period progressed and more shares entered the securities lending market.

SpaceX closed its initial public offering on June 15, 2026, raising approximately $85 billion in gross proceeds, including full exercise of the underwriters' overallotment option. A week later, on June 22, the company priced a $25 billion inaugural bond issuance, which included $7.0 billion of 5.350% senior notes. The IPO itself was preceded by regulatory groundwork in Europe: SpaceX's EU Prospectus for its Class A common stock was approved by BaFin, Germany's Federal Financial Supervisory Authority, on June 5.

Nasdaq added SPCX to the Nasdaq-100 index effective July 7, according to Reuters — a move that typically forces passive index-tracking funds to buy the stock. At that point, SPCX shares had gained about 1% since debut. That modest gain has since been wiped out and then some.

The rapid escalation in short interest over roughly four weeks is notable for its velocity. SPCX went from 5–7% of free float shorted in late June to above 26% by mid-July. Ortex identified SPCX as the biggest mover in short interest across its coverage universe, with the short-interest-to-free-float ratio jumping from 3.65% to 26.27% — a gain of nearly 23 percentage points.

For context, short interest above 20% of free float places a stock in territory that, across the broader market, is relatively rare and typically associated with either deep fundamental disagreement among investors or a specific catalyst-driven thesis. In SPCX's case, the borrow cost at 1–3% annualized suggests that the market for lending the stock is well-supplied — there is no significant short squeeze risk baked into the financing cost, unlike situations where borrow fees spike into double or triple digits as lendable supply tightens.

The $8.7 billion in paper profit reported by Reuters is a mark-to-market figure as of July 16. It reflects the gap between the average short sale price and the prevailing market price, not realized gains. Shorts remain exposed to any price reversal — and SPCX's addition to the Nasdaq-100 means passive buying pressure will continue regardless of fundamental sentiment.

The convergence of factors here is worth laying out plainly: a mega-cap IPO pricing at a level that, within weeks, the market judged too high; a rapidly expanding securities lending supply that kept borrow costs low; passive index inclusion that created a structural bid; and a short-selling community that grew from cautious to maximal in under a month. Whether the shorts are right on the fundamentals is a separate question from whether the trade mechanics favor them — and for now, the mechanics do.

In my view, the SPCX short story is less about SpaceX-specific skepticism than about the mechanics of shorting a newly public mega-cap with abundant lendable supply. When borrow costs sit at 1–3%, the carrying cost of a short position is negligible relative to the potential downside capture. That dynamic, combined with a stock that priced into a market that has since re-rated it lower, created conditions where shorting was cheap, available, and directionally rewarded. The open question is whether Nasdaq-100 passive inflows, continued business execution, or some combination eventually forces shorts to cover — or whether SPCX joins the list of high-profile IPOs where the post-debut optimism simply ran ahead of the stock.