What Is a Short Squeeze? | How Do Stocks Work?

A short squeeze happens when a heavily shorted stock rises sharply and short sellers rush to buy shares back to limit their losses, and that buying pushes the price up even further. It feeds on itself until the forced buying runs out.

Why it happens

A short seller borrows shares, sells them, and hopes to buy them back later at a lower price. To close the position, they have to buy. When the price rises instead:

Losses grow, and there is no ceiling on how high a price can go.
Brokers demand more collateral through margin calls. See margin trading explained.
Some short sellers buy to cover, voluntarily or because the broker closes the position for them.
That buying adds demand, the price rises again, and more shorts are squeezed.

Squeezes are most likely when short interest (shares sold short as a share of the float) is high and the stock is thinly traded, so a burst of buying moves the price a long way. See liquidity. The mechanics of borrowing and short-interest data are covered in how short selling works.

A worked example

A trader shorts 100 shares of Maple Widgets Inc. (hypothetical) at $20, receiving $2,000.

Price rises to $60. Buying back costs $6,000: a $4,000 loss, twice the original sale.
Price rises to $100. Buying back costs $10,000: an $8,000 loss.

A buyer at $20 can lose at most $2,000. A short seller’s loss has no fixed limit, which is why a fast rise can turn into a scramble.

The GameStop example

The best-known recent case is GameStop in January 2021. The SEC staff report on those events found GameStop’s short interest reached 122.97% of its float that month, possible because the same shares can be lent more than once. The stock closed at $347.51 on January 27, 2021, against just under $20 at the end of 2020 (prices before its 2022 stock split).

The report also found that buying to cover was a small fraction of overall buying. In the staff’s words, “it was the positive sentiment, not the buying-to-cover, that sustained the weeks-long price appreciation.” The full story is in what happened with GameStop.

Why squeezes are dangerous for buyers too

Squeezes end, often abruptly. GameStop fell more than 86% from its January 28 intraday high to its close a little over a week later. People who bought late, hoping to ride the squeeze, took the largest losses. Chasing a fast-moving stock is one of the patterns covered in investor behavior mistakes.