Short selling means selling shares you do not own, after borrowing them, with the aim of buying them back later at a lower price. A short seller profits if the price falls and must return the borrowed shares whatever the price has done. It requires a margin account and a broker that can find shares to borrow, and it carries a different risk from buying an asset and waiting for it to rise.
This guide explains how a short position is opened and closed, shows the arithmetic with invented prices, explains why losses are not capped in the same way as a long position, and sets out the costs and recall risks. The figures are illustrative, and the rules for borrowing differ by market and broker.
What is short selling?
In a short sale, you borrow shares through your broker and sell them at the current price. You owe the lender the same number of shares, so you must buy them back and return them later. The difference between the sale price and the buy-back price, after costs, is the profit or loss.
Short selling is more involved than buying. The broker must locate shares that can be borrowed, the lender can ask for them back, and the proceeds and the margin requirement are held as collateral. Those features are why short selling is generally available only in margin accounts, and only for shares that the broker can source. Check the rules in your market before assuming the option exists.
How does the arithmetic work?
The table below shows an illustrative short position of 100 shares. The trader borrows 100 shares at 50 and sells them, then closes the position at a later date. The figures ignore borrowing fees and interest, which are covered below.
| Step | Price | Value of the 100 shares | Result |
|---|---|---|---|
| Sell the borrowed shares | 50 | 5,000 received | Proceeds held in the account |
| Scenario A: price falls to 40 | 40 | 4,000 to buy back | Profit of 1,000 |
| Scenario B: price rises to 60 | 60 | 6,000 to buy back | Loss of 1,000 |
In scenario A the trader buys back at 4,000 and keeps the difference. In scenario B the same trader must pay 6,000 to return shares that were sold for 5,000. A correct call on the direction of the price produces a profit, and a wrong call produces a loss of the same size, before costs. The sale proceeds do not belong to the trader in the way a bought asset does, because they must be used to return the shares.
Why can losses exceed the amount sold?
A long position can lose at most the amount invested, because a share cannot fall below zero. A short position has no such limit, because a share price can rise without a fixed ceiling. The loss grows with the price, so a sharp rally can produce a loss far larger than the proceeds of the sale.
In the example above, a rise from 50 to 100 would make the buy-back cost 10,000 against proceeds of 5,000, a loss of 5,000 on a position that began with 5,000 of proceeds. The loss equals the full value sold short, and more if the price keeps rising. That is why short positions usually require a stop, a margin buffer and a strict limit on size, and why many traders treat a short of a given size as riskier than a long of the same size.
What does borrowing cost?
Short sellers pay a fee to borrow shares, and the fee can rise for shares that many traders want to short. Any interest on collateral and any dividends paid while the position is open also reduce the result. These costs can turn a correct view on the price into a loss.
Borrowing fees are easy to overlook because they are not always shown on the first screen. Check the current fee and its history before opening a position, and include it in the expected result. A short that is correct but expensive to hold can still lose money, which matters for any trader who plans to keep a position open for a long time.
What is recall risk and a short squeeze?
Recall risk is the chance that the lender takes back the shares, forcing you to close the position at a time you did not choose. A short squeeze happens when a rising price forces many short sellers to buy back at once, which adds to the rise. Both risks are hardest to plan for in thinly traded shares.
The defence is planning rather than prediction. Know whether the shares can be recalled, how many shares are on loan and how thinly the stock trades. Set a stop that assumes a sudden rise, and size the position so that a squeeze would not force a loss you cannot accept.
Is short selling suitable for you?
Short selling suits experienced traders with strict stops, enough capital to meet margin needs and a clear understanding of borrowing costs and recall. It is not a casual way to hedge, and it is not a guaranteed way to profit from a falling market. A falling price can reverse, and the cost of waiting can exceed the gain.
Test any short rule on past data before using it, and count every short trade, including the ones that squeezed. Size positions for the possibility of a sharp rally, and decide in advance when you will close a short that is going against you.
How should you size and manage a short position?
Size a short position from the loss at a sharp rally, not from the price at which you entered. Set the stop before opening the position, and check the borrow fee and availability each day. Treat any short as a position that can gap against you.
Work out the loss at a sharp rise, such as a 30 percent move in the price, and check that the account could absorb it without a forced close. The size that looks sensible at a 5 percent rise may be too large at 30 percent. Scale the position down until the stress case is acceptable.
Review the position at each session. Note the current borrow fee, the number of shares on loan and any news that could cause a squeeze. A short that is correct on price can still close at a loss if the fee rises or the shares are recalled.
Common mistakes
Ignoring the borrowing fee. A short that looks profitable on price can lose money once the fee is charged, day after day.
Opening a short without a stop. Losses on a short position are not capped in the way a long position's are, so a stop is essential.
Treating a falling price as a certainty. Prices can reverse quickly, and a short that is not managed can turn a small loss into a large one.
Checklist
- Confirm that your broker can borrow the shares and what the current fee is.
- Check how many shares are on loan and how thinly the stock trades.
- Calculate the loss at a sharp rally, not only at a modest one.
- Set a stop before opening the position, and decide what would invalidate the idea.
- Size the position so that a squeeze would not force a loss you cannot accept.
- Include dividends and interest in the expected result.
- Record every short trade and its costs, so the results can be judged honestly.
Key takeaways
Short selling borrows shares, sells them and buys them back later, profiting if the price falls. Losses are not capped at the amount sold, because the price can rise without limit, so a stop and a size limit are essential. Borrowing fees, dividends and recall risk all affect the result, and a short squeeze can move the price against a seller quickly.
This guide is for general information, not financial advice. See the disclaimer.