Behind every share price is a tug of war between buyers and sellers. Short interest tells you how many traders are betting that the price will fall. It is a useful piece of information, but it is often misunderstood, especially by beginners who see a high number and assume a squeeze is on the way.
What short interest is
When a trader sells a stock short, they borrow shares, sell them and hope to buy them back later at a lower price. Short interest is the total number of shares that have been sold short and not yet bought back. It is usually expressed in two ways: as a raw number of shares, and as a percentage of the shares available for trading, known as the free float.
In the US, exchanges publish short interest data twice a month. In the UK and Europe, regulators require investors to disclose large individual short positions above certain thresholds, which gives a partial picture of who is betting against a company.
Days to cover
Another common measure is the short interest ratio, or days to cover. It divides the number of shares sold short by the average daily trading volume. The result is a rough estimate of how many days it would take short sellers to buy back all their shares if they had to. A high days-to-cover figure means short sellers could struggle to exit quickly.
What high short interest can mean
High short interest shows that a significant number of investors believe the stock is overvalued or that the company faces problems. Some short sellers are professional researchers who have studied the company closely, so it is worth taking their view seriously.
It can also create the conditions for a short squeeze. If the share price rises sharply, short sellers face growing losses and may rush to buy back shares, which pushes the price even higher. Our guide to short squeezes explains how that chain reaction works.
What it does not tell you
High short interest does not guarantee a squeeze. Many heavily shorted companies keep falling because the short sellers were right. Short interest data is also delayed, so it may not reflect positions taken in the last week or two. And some short positions are hedges rather than outright bets, for example a fund that owns convertible bonds and shorts the shares to manage risk.
Low short interest is not a guarantee of safety either. It simply means fewer investors are actively betting against the stock.
How traders use it
Traders often combine short interest with other information. A heavily shorted stock with improving fundamentals or a positive catalyst may be vulnerable to a squeeze. A heavily shorted stock with weakening results may be confirming a bearish thesis. The borrowing cost of shares, known as the borrow fee, can also reveal how crowded the short side has become.
Common mistakes
The most common mistake is buying a stock only because short interest is high, hoping for a squeeze. That is a bet on other people’s pain rather than on the company, and it can go badly wrong. Another mistake is ignoring the reasons behind the shorts. Reading the bear case is one of the best ways to test your own view.
The beginner takeaway
Short interest is a sentiment gauge, not a signal on its own. Use it to understand the debate around a stock rather than to predict the next move. If you want to see how carefully you test your own trading ideas, take the free Samuel & Co Trading Trader Assessment.
