Short selling explained: how it works, what it costs and where it goes wrong

A trader sells 1,000 shares of a company at 50 dollars each and collects 50,000 dollars. The trader never owned those shares. They were borrowed an instant earlier from a pension fund's holdings through a broker, and they have to be returned one day, bought back at whatever the price is then. At 40 dollars, the trader keeps about 10,000 dollars. At 100 dollars, the trader owes 50,000 dollars more than the sale brought in.

That is short selling: selling borrowed securities in the expectation of buying them back later at a lower price. The profit is the fall in price, minus the cost of borrowing. The loss is the rise in price, plus the same costs, and a price can rise without limit.

How a short sale works, from locate to buy-to-cover

For an investor at a US broker, a short sale on a listed stock runs in this order:

1. Margin account. Short sales can only be made in a margin account, because the broker is lending something and wants collateral.
2. Locate. Before accepting the order, the broker must have borrowed the shares, arranged to borrow them, or have reasonable grounds to believe they can be borrowed in time for delivery. This is the locate requirement of Rule 203(b)(1) of Regulation SHO.
3. Sale. The shares are sold on the market like any other sale. The buyer receives ordinary shares and has no idea they came from a short seller.
4. Collateral. The sale proceeds stay in the account, and the investor adds margin on top. At the institutional level the lender holds cash collateral of typically 102% or 105% of the value of the loan, marked to market every day.
5. Carrying costs. While the position is open the short seller pays a borrowing fee and pays the lender an amount equal to any dividend the company distributes, because the lender would have received that dividend.
6. Buy-to-cover. To close the position, the short seller buys the same number of shares on the market and the broker returns them to the lender. This purchase is called covering.

The lender keeps its economic exposure the whole time. A pension fund that lends its shares still gains or loses on them, still receives the equivalent of the dividends, and earns the lending fee. It gives up the right to vote those shares while they are out on loan. Securities lending earned lenders a record 15.3 billion dollars worldwide in 2025, and pension funds earned more than 700 million dollars from it in 2023.

What borrowing the shares costs

The borrowing fee is quoted as an annual percentage of the value of the shares and charged daily for as long as the loan is open. For most large, liquid stocks the fee is small. Across US equities on loan, the average lending fee was about 33 basis points a year, or 0.33%, over the three days covered by a pilot survey of agent lenders by the Office of Financial Research. In 2000 and 2001, 91% of the US stocks on loan cost less than 1% a year to borrow, with easy-to-borrow stocks averaging 0.17%.

The other 9% are called specials, and they averaged 4.3% a year over the same period. Heavily shorted stocks go far higher. GameStop cost around 25% a year to borrow in January 2021, and broker rates on the hardest-to-borrow names can reach more than 100% a year. The rate can change overnight while the position is open.

Rebates on the cash collateral

Institutional short sellers such as hedge funds see the fee in a different form. They post cash collateral, the lender invests that cash, and the lender pays back part of the interest earned as a rebate. The rebate is the reinvestment rate minus the lending fee, and it is usually negotiated as a spread to a reference rate, most commonly the Overnight Bank Funding Rate. On an easy-to-borrow stock the short seller earns a rebate close to short-term interest rates. On a special, the fee can exceed the interest earned, and the rebate turns negative: the short seller pays the lender on top of giving up the interest on its own cash.

Retail accounts usually see a simpler version: the broker charges interest on the value of the borrowed shares, accrued daily and deducted monthly.

Margin on a short sale: Regulation T and FINRA Rule 4210

At the moment of the sale, Regulation T from the Federal Reserve requires margin equal to 150% of the value of the security sold short. The proceeds count for 100%, so in practice the investor adds 50% of the position's value in cash or securities.

After that, FINRA Rule 4210 sets the minimum equity the account must keep every day:

These are floors. Brokers can and often do set higher house requirements, especially on volatile or heavily shorted stocks.

Margin call price and 90-day costs on a 50,000 dollar short

Go back to the 1,000 shares sold at 50 dollars. Regulation T requires 75,000 dollars in the account: the 50,000 dollars of proceeds plus a 25,000 dollar deposit. The account's equity is that 75,000 dollars minus the current cost of buying the shares back.

FINRA's 30% minimum is breached when the equity falls below 30% of the shares' market value. That happens once the value of the shares passes 75,000 divided by 1.3, or 57,692 dollars. At a share price of about 57.69 dollars, a rise of 15%, the broker issues a margin call. If the investor cannot add cash, the broker buys the shares back and closes the position.

Now add costs over a 90-day holding period. Suppose the stock is easy to borrow at 0.33% a year and pays one quarterly dividend of 0.40 dollars a share.

The fee here is small. On a special borrowed at 25% a year, the same 90 days would cost about 3,082 dollars in fees, which wipes out a third of the profit in the first row before any price move.

A long position in the same stock can lose at most the 50,000 dollars invested. The short position lost twice the deposit, and a stock can go to 200 dollars or 500 dollars. In practice the broker would have closed the position long before 100 dollars, but a price that gaps up overnight on a takeover bid or trial result can jump past the margin call level before anyone can act.

Short squeezes and the GameStop episode of January 2021

A short squeeze happens when a heavily shorted stock rises and short sellers have to buy it back at the same time, by choice, through stop orders or because of margin calls. Their buying pushes the price higher, which forces more covering.

By January 2021 GameStop's short interest had reached 122.97% of its float, meaning more shares had been sold short than were freely available to trade. The stock closed at 19.95 dollars on January 12. On January 27 it closed at 347.51 dollars, and on January 28 it touched an intraday high of 483 dollars. Both prices are from before the company's four-for-one stock split in July 2022.

Melvin Capital, one of the best known short sellers of the stock, lost 53% in January. Citadel and Point72 put 2.75 billion dollars into the firm on January 25, and Melvin closed its GameStop short the next day. In May 2022 it announced it would wind down and return its investors' money.

Trading records from January 2021 show who was buying and why brokers restricted the stock:

• Short covering was a small part of the buying. Purchases to close short positions were a small fraction of total buy volume, and the price stayed high after the direct effect of covering would have faded. Between January 22 and 27 the price rose while short interest was falling. Most of the buying came from investors opening new positions on positive sentiment, the herd behavior covered in our article on behavioral finance biases.
• Clearing house collateral calls came before the broker restrictions. On January 27 the National Securities Clearing Corporation made intraday margin calls totaling 6.9 billion dollars on 36 clearing members. The next day one retail broker restricted eight stocks, GameStop and AMC among them, to closing trades only. Robinhood said its deposit requirements had increased tenfold.
• The stock stayed expensive to borrow. GameStop cost roughly 25% a year to borrow in January 2021. Lending fee observations from January 2007 to July 2018 averaged 1.5% a year in SEC staff data, a longer and broader sample than the three-day survey behind the 0.33% average quoted earlier.

Two numbers help spot squeeze risk before it happens. Short interest is the number of shares sold short and not yet covered, as a percentage of the float. Days to cover is short interest divided by average daily trading volume, the number of normal trading days it would take all short sellers to buy back. FINRA collects short interest from brokers twice a month and publishes it seven business days after each reporting date, so the figures are always one to three weeks old.

Regulation SHO: the locate, the close-out and the alternative uptick rule

The SEC's main short selling rulebook, Regulation SHO, was adopted in 2004 and took effect on January 3, 2005. It has three working parts.

The locate. Rule 203(b)(1) bars any short sale in an equity security unless the broker has borrowed the shares, arranged to borrow them or has reasonable grounds to believe they can be borrowed.

The close-out. If a short sale fails to deliver on settlement date, Rule 204 requires the broker's clearing firm to close out the failure by borrowing or buying shares no later than the start of regular trading on the next settlement day. Since US stocks moved to one-day settlement on May 28, 2024, that means by the market open two trading days after the trade. Failures from long sales get until the third settlement day after settlement date.

The alternative uptick rule. The original uptick rule, which allowed short sales only at a price above the last different trade price, dated from 1938 and was eliminated in July 2007. The SEC adopted a narrower replacement, Rule 201, in February 2010. It switches on only when a stock falls 10% or more from the previous day's close. For the rest of that day and all of the next, short sales cannot be executed or displayed at or below the national best bid.

Naked short selling means selling short without borrowing or locating the shares. Market makers have limited exceptions to the locate rule. For everyone else, a short sale without a locate breaks Regulation SHO, and any resulting failure to deliver has to be closed out under Rule 204.

The SEC can also stop short selling outright in an emergency. On September 19, 2008 it banned short sales in an initial list of 799 financial stocks. The ban was extended once and expired on October 8, 2008.

Disclosure of short positions in 2026: Form SHO and Rule 10c-1a

After GameStop, the SEC adopted two transparency rules on October 13, 2023. Compliance with neither is required yet.

Rule 13f-2 and Form SHO require institutional investment managers to report large short positions to the SEC each month, within 14 calendar days of month-end. For a listed company the threshold is a monthly average gross short position of 10 million dollars or 2.5% of the shares outstanding. For a company that does not file SEC reports it is 500,000 dollars on any settlement date in the month. The SEC would publish the data in aggregate by stock, without naming the managers.

Rule 10c-1a requires the terms of securities loans, including the fees, to be reported to FINRA, which would publish them. Lending fees are negotiated privately today.

Several events have pushed both rules back:

• On August 25, 2025 the Fifth Circuit, ruling on a challenge by private fund managers, sent both rules back to the SEC without vacating them, so that the agency could consider and quantify their combined economic impact.
• On September 5, 2025 SEC Chairman Paul Atkins asked the staff to recommend changes to both rules and to their compliance dates.
• An SEC order of December 3, 2025 moved the first Form SHO compliance date to January 2, 2028. Securities lending reports under Rule 10c-1a are due from September 28, 2028, with public release from March 29, 2029.
• The SEC's regulatory agenda lists amendments to Rule 13f-2, Form SHO and Regulation SHO as a deregulatory proposal targeted for October 2026.

FINRA also tried to speed up short interest data in 2026. Its proposal for weekly reporting, filed in May, was withdrawn on August 5, 2026, so reporting stays twice a month.

Activist short sellers

Some short sellers publish their research. An activist short seller takes a short position, releases a report arguing the company is overvalued or fraudulent, and profits if the market agrees. The targets are often companies whose accounts the seller believes are false.

Three published short campaigns, and how each one ended:

Enron

Jim Chanos's firm began shorting Enron in November 2000 after reading its SEC filings. Enron filed for bankruptcy on December 2, 2001.

Wirecard

The short seller Fraser Perring, writing as Zatarra Research, published a report on Wirecard's accounts in 2016. After further Financial Times reports, Germany's regulator BaFin banned new short positions in the stock in February 2019. Wirecard filed for insolvency in June 2020 after 1.9 billion euros of cash turned out to be missing.

Adani Group

Hindenburg Research published a report on the Indian conglomerate on January 24, 2023, alleging stock manipulation and undisclosed related-party dealings, which the group denied. Within ten days the group's companies had lost more than 100 billion dollars in market value. Hindenburg's founder Nate Anderson disbanded the firm on January 15, 2025. In September 2025 India's market regulator SEBI found no violation in two final orders covering Adani Enterprises, Adani Ports and Adani Power. In September 2026 five group companies settled separate SEBI proceedings for 1.51 crore rupees over alleged lapses in disclosing related-party transactions.

Stocks targeted by hedge funds that published short research showed a mean abnormal return of minus 56.8% over the following 12 months, and 80 of the 113 targets fell relative to the market. About 30% of short attacks are followed by a price rise on the first day, and campaigns caught in a squeeze lost an average of 70 million dollars, against 35 million dollars of profit on a successful one.

Publishing a short thesis also carries legal risk when the trading contradicts the words. In July 2024 the SEC charged Andrew Left of Citron Research with a 20 million dollar scheme, alleging he recommended positions publicly and then traded against his own recommendations as prices moved. In June 2026 a federal jury found him guilty of one count of securities fraud scheme and 12 counts of securities fraud.

How hedge funds use short selling in long/short portfolios

Short selling is where hedge funds got their name. In 1949 Alfred Winslow Jones started a fund with 100,000 dollars that bought stocks he liked and sold short stocks he did not, so that a market-wide fall hit both sides at once. Our guide to what a hedge fund is traces how that structure became an industry.

Equity hedge, the strategy category that includes long/short equity funds, managed 1.76 trillion dollars at the end of June 2026, about a third of the industry's record 5.6 trillion dollars. Funds such as Tiger Global and Lone Pine, both on our list of notable hedge funds, built their names in this strategy.

Two measures describe a long/short book. Take a fund with 100 million dollars of capital, 130 million dollars of long positions and 80 million dollars of short positions:

• Gross exposure is longs plus shorts divided by capital: 210%. It measures how much is at stake in total, and how much the fund is borrowing to do it.
• Net exposure is longs minus shorts divided by capital: 50%. It measures how much the fund gains or loses if the whole market moves.

If the market falls 10% and every stock moves with it, the fund loses about 5% instead of the 10% a fully invested long-only fund would lose. With 50% net exposure, half of any market move reaches the fund, and the rest of its result depends on whether its longs beat its shorts. Gross leverage among global long/short funds tracked by Goldman Sachs' prime brokerage reached a record 213.2% at the start of 2026, close to the example above.

A fund's short side has a return of its own. Every dollar of short positions earns the rebate on its cash collateral, pays the borrowing fee and the dividends, and gains or loses the price change. When interest rates are high and the shorts are easy to borrow, the rebate adds to returns. When the shorts are crowded names, the fees go up and the risk of a squeeze on several of them at once, as in January 2021, goes up with them.

Other ways to profit from a falling price

Buying a put option

The right to sell shares at a set price before a set date. The loss is capped at the premium paid, no borrowing is needed, and the option loses value as time passes if the stock does not fall.

Inverse ETFs

Funds that aim to return the opposite of an index over one day. Because they reset daily, their return over weeks or months can differ widely from the inverse of the index return.

Short futures and swaps

Contracts that gain when the price of an index, commodity or single stock falls. Hedge funds use them to short whole markets without borrowing individual shares.

This article is general information, not investment advice.

Frequently asked questions

Is short selling legal?

Yes. Short selling is legal in the United States and regulated by the SEC under Regulation SHO, which requires the broker to locate shares before the sale and to close out any failure to deliver. Naked short selling that abuses those rules can be illegal, and the SEC can restrict short sales in an emergency, as it did for about three weeks in 2008 on an initial list of 799 financial stocks.

How long can you keep a short position open?

No rule sets a maximum. A short position stays open as long as the account meets its margin requirement, the borrowing fee is paid and the shares remain available to borrow. The broker can recall the loan or close the position if the lender wants the shares back, if the stock becomes hard to borrow or if a margin call goes unmet.

What happens if a shorted stock goes to zero?

The short seller keeps the full proceeds of the sale, minus borrowing fees and any dividends paid to the lender along the way. That is the largest possible gain on a short sale: 100% of the price received. When a company is delisted or goes bankrupt, the broker handles how the borrowed position is closed, which can take time.

How can short interest be above 100% of the float?

The same share can be lent more than once. A short seller borrows a share and sells it, the buyer holds it in a margin account, and the buyer's broker can lend it again to another short seller. GameStop's short interest reached 122.97% of its float in January 2021.

What is the difference between short selling and buying a put option?

A short seller borrows and sells shares, pays borrowing fees and dividends, and faces a loss with no fixed limit if the price rises. A put buyer pays a premium for the right to sell at a set price before a set date. The most a put buyer can lose is the premium, but the option can expire worthless if the stock does not fall far enough in time.