What is a short squeeze?
A short squeeze is a fast rise in a stock's price driven, in large part, by short sellers buying shares back to close their positions.
To sell short, a trader borrows shares, sells them, and hopes to buy them back later at a lower price. If the price rises instead, the loss grows with every cent, and there is no ceiling on how high the price can go. At some point many short sellers buy back, some by choice and some because their broker requires it. Those purchases are extra demand on top of the buyers who were already there, and they push the price up further. That pushes more short sellers to buy back, and the loop feeds itself.
Squeezes are part of why small caps sometimes move far more than any news would explain. They are also why a move can stop abruptly: once the forced buying is done, the extra demand is gone.
This guide covers the numbers traders look at, why low float small caps squeeze hardest, what a squeeze tends to look like, and the risks for anyone who buys into one.
The numbers traders look at: short interest, days to cover, cost to borrow
Short interest is the number of shares that have been sold short and not yet bought back. It is usually shown as a share of the float. A short interest of 30% means that, for every 100 shares free to trade, 30 have been borrowed and sold, and will have to be bought back at some point.
Short interest is published twice a month, with a delay of about two weeks. The number you see can be weeks old, and on a small cap that moved hard since, it may say little about where short sellers stand today.
Days to cover divides short interest by the average daily volume. If 3 million shares are short and the stock usually trades 1 million a day, days to cover is 3: on a normal day, it would take three sessions of the whole volume for short sellers to buy back. The higher it is, the harder it is for short sellers to leave quickly. On the day of a big move, when volume is many times its usual level, that number shrinks fast.
The cost to borrow is the fee short sellers pay to keep borrowed shares. When few shares are available to borrow, the fee rises, sometimes very high, and brokers may mark the stock as hard to borrow. A high and rising fee means holding a short position is getting expensive, which adds pressure to close it.
None of these numbers is a signal on its own. Together they describe how much fuel is there, not whether anything will light it.
Why low float small caps squeeze hardest
A squeeze needs two things: a lot of shares that must be bought back, and few shares available to buy. Low float small caps often have both.
On a stock with a small float, short interest can be a large share of all the shares that trade. When the price starts to rise on news, short sellers and new buyers compete for the same small supply. The guide to low float stocks explains why that thin supply makes moves so large in both directions.
Volume is what turns the fuel into a move. A heavily shorted stock that trades a normal amount is just a heavily shorted stock. When volume jumps to many times its usual level, with a high RVOL, it often means new buyers have arrived and short sellers are under pressure; the guide to relative volume explains how that is measured.
There is also a rule that can change the balance during a drop. When a stock falls 10% or more from the previous day's close, a short sale restriction applies for the rest of that day and the next: short sales are only allowed at a price above the best bid. It makes it harder to press a stock down with new short sales, and traders keep it in mind on the day after a big drop. The guide to the SSR rule covers when it starts and what it changes.
What a squeeze tends to look like
Every squeeze is different, but traders describe a few common features. What follows describes, it doesn't prescribe.
- A catalyst first. News, a filing or a sector move starts a rise that short sellers didn't expect.
- Volume many times normal. Not a slow drift up, but heavy, fast buying, often with repeated halts on the way up.
- Moves that ignore resistance. Levels that would usually slow a stock down give way quickly, because some of the buying is forced and doesn't care about price.
- A rising cost to borrow. As shares to borrow run out, the fee climbs, and the stock may stop being available to short at all.
- A sudden end. When the buying that had to happen is done, there may be few buyers left at the top, and the drop can be as fast as the rise.
An illustrative example, with made-up numbers
Stock A has a float of 8 million shares, and its latest short interest, two weeks old, is 3 million shares: about 37% of the float. It usually trades 1 million shares a day. One morning it releases news and opens at 2 dollars, up from 1.60. By 10:30 ET it has traded 12 million shares, one and a half times its whole float, and reaches 3.40 after two halts on the way up. Shortly after, the company files to sell new shares, and the stock falls back to 2.30 by the afternoon.
How many short sellers covered that morning, nobody outside can know for sure: the short interest figure was weeks old, and the new shares changed the supply. What the example shows is the shape: a catalyst, volume far beyond the float, a fast run, and an end that came from outside the chart.
The risks of trading a squeeze
Squeezes draw traders because the moves are large. The risks are just as large.
Buying late. By the time a squeeze is obvious, much of it may be done. The traders who bought early, and the short sellers who just covered, can be the sellers at the top.
Old data. Short interest is published twice a month with a delay. A stock that looks heavily shorted on paper may have seen most of its short sellers leave already.
New shares. Companies whose stock just rose sharply often sell new shares into the move. New supply can end a squeeze in minutes.
Halts and gaps. Squeezing stocks halt often, and can reopen far from where they stopped, on either side. Stops don't protect a position during a halt.
The story effect. A squeeze becomes a story quickly, and stories bring buyers who are betting on the story rather than the stock. When that demand fades, the drop can be steep.
Many traders who trade squeezes trade smaller than usual, take partial profits into strength, and decide in advance where they are wrong. Practicing on past squeezes, including the ones that failed, is how they find out whether they can follow those rules when a stock is moving that fast. The guide to practicing day trading covers how to do that on past sessions, without money at risk.