How MiniMed ended up with 99% of its float sold short
An anomaly appeared on the Nasdaq stock exchange yesterday when, per an estimate by data provider Ortex, 99% of the shares in public medical tech company MiniMed Group Inc.’s float were sold-short.
In contrast to buyers, short-sellers borrow stock to sell first, hoping to repay shares at a lower price to close their loan with profit.
Up from 47.6% on September 15 and 77% a week earlier, MiniMed’s short interest skyrocketed to an almost unbelievable high yesterday as short-sellers borrowed and sold almost the entire float, i.e. every share of the company available for public trading on Nasdaq’s exchange.
Ortex specializes in live short interest estimates for publicly traded companies. It updates data daily from securities-lending data, often days ahead of official, twice-monthly exchange reports.
According to its data from securities lenders, shares of MiniMed’s common stock on loan nearly equaled the company’s full float yesterday, with available stock to borrow at just 0.08% of short interest.
A swap arrangement with a Friday deadline
Understanding this anomaly begins with another publicly-traded company, Medtronic, which incubated MiniMed.
Indeed, MiniMed used to be Medtronic’s diabetes business before Medtronic spun it off in a March 2026 IPO.
As of September 14, Medtronic still owned 90% of MiniMed and was offering a tax-free exchange of 225.3 million shares of MiniMed’s common stock, MMED, for Medtronic’s common stock, MDT.
Although there are 1.28 billion shares in Medtronic’s float — plenty to allow for that conversion while maintaining orderly trading — MiniMed only has 28.5 million shares in its float.
In other words, Medtronic’s share swap offer is seven times larger than MiniMed’s entire tradable supply.
To be fair, shares aren’t converting on a 1:1 basis. Medtronic set an upper cap limiting conversion to 4.5939 MiniMed shares per Medtronic share.
Still, 225.3 million shares more than covers MiniMed’s float.
Moreover, unless extended, the offer expires at midnight on Friday. So the time to act was yesterday.
Medtronic, the parent company, created and owns the vast majority of MiniMed shares. Indeed, MiniMed’s float started changing hands in retail trading when Medtronic offered 28 million in MiniMed’s IPO.
Medtronic owns the rest: an additional 253 million restricted shares of MiniMed.
Medtronic has all the shares, so arbitrageurs go 99% short
The whole arrangement is a textbook arbitrage scenario.
This week, i.e. before the Friday deadline, investors have been able to buy Medtronic stock, tender it to accept Medtronic’s offer, and short the MiniMed shares they expect to receive in return.
Medtronic is large and credible, so the deal will almost certainly execute. Guessing how close the conversion ratio would reach toward Medtronic’s upper limit of 4.5939:1 was the only hard part.
Barron’s reported on October 2, for example, that MiniMed had slid about 12% since the eve of its Medtronic offer, saying arbitrageurs’ selling pressure is the likely culprit behind MiniMed’s lower stock price.
The arithmetic is simple. Because slightly less value of Medtronic stock can buy slightly more value of MiniMed stock, that slight premium has become the arbitrageurs’ prize.
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They bought Medtronic to short MiniMed
Traders who short the MiniMed shares can buy Medtronic shares, and the swap supplies the MiniMed shares to repay their loans and close their short-sales in profit.
Directly incentivized to sell as much MiniMed short as possible, short sellers have rationally gobbled up to sell-short almost every available loan of MiniMed’s float.
Unconcerned, they expect Medtronic’s share conversion to execute within the next few trading days, allowing them to repay their borrowed short-sale and close their trade with a slight profit.
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