Short Selling (공매도)
A trade in which you borrow shares, sell them first, then buy them back later at a lower price to return them and pocket the difference — a way to bet on a price decline.
Short profit/loss = price sold after borrowing − price bought back later (− stock borrow fee)
A high short interest means "there's a lot of stock sold on a bet that the price will fall," but it doesn't guarantee the price will actually drop.
In plain terms
Normally you make a difference by "buying low and selling high." Short selling flips that order. You borrow shares and sell them high first, then if the price falls later, you buy them back low and return them. That difference is the gain.
In other words, short selling is a way to bet that "this stock will fall." If it falls you gain; if it rises you lose.
What it tells you
When short selling piles up in a stock, it is sometimes read as a supply-and-demand signal that some investors view the company negatively (that its price is above its value, or that something is wrong).
But borrowed shares must eventually be bought back and returned. So if the price rises contrary to expectations, buying rushes in to limit losses, and the price can instead surge (this is called a short squeeze).
Formula
Short profit/loss = price sold after borrowing − price bought back later (− stock borrow fee) Short interest ratio = shares sold short ÷ share count Days to cover = short interest ÷ average daily trading volume ※ Some sources use the float in the denominator and others use shares outstanding, so the ratio can look different across sources for the same stock.
What high or low means
A high short interest means "there's a lot of stock sold on a bet that the price will fall," but it doesn't guarantee the price will actually drop. The very same high figure can be ① a sign of a negative outlook, or ② fuel for a sharp rise through a short squeeze — the direction depends on the context.
So rather than deciding on a direction from a short-selling figure alone, it means more when you look at it alongside the company's fundamentals (financials and earnings).
"Lots of short selling = a bad stock, period" is a misunderstanding. Short selling also serves to correct prices that have been set too far from value, and as mentioned above it can instead become the spark for a sharp rise, as in a short squeeze. The direction can't be pinned to one side.
With short selling, the loss is theoretically unlimited. Unlike buying (where the price can fall at most to 0), there's no ceiling on how far a price can rise, so the more it rises, the bigger the loss for someone who borrowed and sold. That makes it a risky trade.
Short interest is data that U.S. brokerages report to FINRA twice a month. However, it is a total for the whole stock, so which institution sold how much is not disclosed anywhere — that's how it differs from 13F, which tells you how much stock each institution holds. Securities lending data, which shows the lender's side, is a separate source that we don't cover.
In January 2021, individual investors piled collectively into GameStop (GME) — a stock widely seen as failing and heavily shorted — and the price surged more than 20-fold in a single month. Buying back to cap losses (short covering) piled on, and a short squeeze erupted.
Some hedge funds that had sold short took losses in the billions of dollars. But conversely, many individuals who jumped on the frenzy late were also caught at the top and took large losses. It's an episode that showed both the risk of short selling (losses that can grow without limit) and the risk of a bubble created by supply and demand.
Metrics to read alongside
Guides that cover this term
In Stocklore
Stocklore does not cover Short. Instead, it shows insider buying and selling (Form 4) and how institutions changed their holdings each quarter (13F).
This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.