Short selling means selling borrowed shares first and buying them back later. Here is how gains and losses arise, how losses grow, and the rules around it.
📚 Reading the numbers in equities · 15/32·⏱ About 6min read·Information updated 2026-10-10
📋 Key facts6
Key point
You borrow shares, sell them first, then buy them back to return them
Payoff
You profit if the price falls and lose if it rises, with no fixed limit on losses
Cost
Borrowing fees accrue, and you may owe an amount equal to any dividend
Rules
Naked short selling, selling without borrowing first, is banned in Korea
Resumption
Resumed for all stocks on 31 March 2025 (banned from 6 November 2023); repayment within 90 days, up to 12 months
Note
This explains structure only and is not investment advice
The structure, step by step
A normal trade buys first and sells later. A short sale flips the order: sell first, buy later. Since you cannot sell shares you do not own, you borrow them from an institution or broker that holds them and sell those. Later you buy the same number of shares in the market and return them, which closes the trade. If you buy back for less than you sold, the difference is your gain; if you pay more, the difference is your loss.
Borrow the shares
Sell the borrowed shares in the market
Later, buy back the same number of shares
Return them to the lender
Why the payoff is lopsided
When you buy a stock, the worst case is that it goes to zero and you lose everything you put in, but no more. Shorting is the reverse. The most you can make is when the price hits zero, while losses keep growing as the price rises. Short a stock at 10,000 won and watch it reach 20,000, and you lose an amount equal to what you sold; at 30,000 you lose twice that. In a market where stocks do sometimes double or triple, that asymmetry is no small matter. It makes short selling hard to handle without a plan for cutting losses.
Collateral and forced buy-ins
Borrowing shares requires collateral, and you must keep it above a set ratio. As the price rises, the shares you owe become worth more, so you are asked to post more collateral. If you cannot, the broker buys the shares and returns them for you, locking in the loss at a moment you did not choose. The lender can also recall the shares, forcing you to close early. Check your broker's terms for the exact ratios and repayment conditions.
Short squeezes
When a heavily shorted stock starts to rise, short sellers rush to buy shares to cap their losses. That buying pushes the price higher, which triggers more buying to close positions, and the cycle can feed on itself. This is called a short squeeze. It is most likely in stocks with a small free float and a large short position, and it can move prices sharply over a short period regardless of what the company is worth.
What borrowing costs
While you hold a short position, borrowing fees build up day by day. Stocks that many people want to borrow, or that few holders lend, carry higher fees and sometimes cannot be borrowed at all. If a dividend record date passes during the short, you may have to pay the lender an amount equal to the dividend they would have received. So even if the price moves your way, a delay lets costs eat into the gain. A short seller is fighting the clock as well as the price.
Its role in markets, and the controversy
Short selling is credited with bringing negative information about overvalued stocks into prices and with adding trading that helps prices form. It is also criticised for adding selling pressure in falling markets, for cases of illegal naked shorting, and for the gap between the borrowing terms available to individuals and institutions. In Korea, short selling of all stocks was banned on 16 March 2020, allowed again for KOSPI 200 and KOSDAQ 150 stocks only on 3 May 2021, banned outright again on 6 November 2023, and resumed for all stocks on 31 March 2025. The rules change often, so check the latest official guidance from regulators and the exchange.
Korean rules since the March 2025 resumption
The rules changed when short selling resumed on 31 March 2025. Naked short selling, selling shares without borrowing them first, remains banned; institutions must check their positions with their own systems, and the Korea Exchange's central short-selling monitoring system checks them again. Penalties for deliberate naked shorting became heavier, including fines of four to six times the unfair gain. The repayment period for shares borrowed for short selling was aligned at 90 days for both individuals and institutions, up to 12 months including extensions, and the collateral ratio for individuals borrowing through a broker's stock lending service was cut from 120% to 105%. The price rule that bars short sale orders below the previous trade price, and the duty to report or disclose positions above a certain size, also still apply. Individuals shorting for the first time must meet requirements such as advance training and simulated trading. This is as of October 2026; check the Financial Services Commission's and your broker's guidance for details.
Naked shorting banned; institutional system checks plus the exchange's central monitoring system
Repayment period: 90 days for individuals and institutions, up to 12 months with extensions
Collateral ratio for individuals 105% (120% before the resumption)
Short orders below the previous price restricted; positions reported and disclosed
Individuals need advance training and simulated trading
Common misconceptions and cautions
A large short interest does not mean a stock must fall. Some shorts hedge other holdings, and a big short position can itself fuel a squeeze. Listed products that move opposite to an index differ from shorting in that you cannot lose more than you paid, but because they reset to a daily return target, holding them for long periods often produces results that differ from expectations. This article explains structure only and is not investment advice.