Short interest is the number of shares sold short and not yet repurchased, usually expressed as a percentage of the float. It measures how much capital is betting the price will fall. It is reported twice monthly, which makes it a lagging picture rather than a live one.
How it is measured
Short interest as a percentage of float is the more meaningful form, since it compares the bet to the shares actually available. Days to cover, or the short interest ratio, divides short interest by average daily volume, estimating how long it would take shorts to close out. Above roughly 5% of float is high; above 20% is unusual and typically means a well-known controversy.
Reporting happens twice a month with a lag of several days, so the figure describes a position that may already have changed.
What high short interest actually means
Most straightforwardly, it means informed capital has done work and concluded the price will fall. Short sellers carry unlimited downside and pay borrowing costs to hold the position, so they tend to be more rigorous than the average buyer. Historically, heavily shorted stocks have underperformed on average.
The popular reading, that heavy shorting sets up a squeeze, has the logic backwards. A squeeze is a possible mechanism, not an expected outcome, and it requires a catalyst that forces covering. Buying something because others think it is going down, in the hope they are forced to buy it back, is a bet on market plumbing rather than on a business.
Where it is genuinely useful
As a prompt rather than a signal. If you like a company and discover 18% of its float is short, the productive response is to find the bear case and see whether it addresses something you had not considered. Short sellers publish, and their work is often the most detailed analysis available on a company.
If their argument is about accounting, customer losses or a narrowing moat, that is worth resolving before you buy. If it is about valuation, you already knew the stock was expensive and they may simply have a shorter horizon than you.
Why it should rarely change a long-term thesis
Short interest describes positioning, not the business. It changes weekly while the things that decide a decade of returns, returns on capital, competitive position and reinvestment, change slowly.
The practical exceptions are narrow: a very high figure is a reason to re-examine your work, and a rising figure alongside deteriorating fundamentals is confirmation rather than news. Beyond that, this is a number about other investors, and what you understand about the company is a better guide than what other people are betting.
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Frequently asked questions
Related
- Float, the denominator that makes short interest meaningful.
- Stock red flags, the problems a bear case usually points at.
- Circle of competence, the better guide to whether to own something.
- Mr Market, how to treat other investors' opinions about your holdings.