What is a Buy-in? Definition, Mechanics, and Example
A buy-in is a forced purchase of securities by a broker or exchange to cover a failed delivery in a short sale.
What is a buy-in?
A buy-in is a compulsory purchase of securities executed on behalf of a seller who fails to deliver shares by the settlement date. In a short sale, the seller borrows shares and sells them, then must deliver those shares to the buyer at settlement. If the seller cannot locate or borrow the shares, or if the lender recalls the shares and the seller cannot replace them, the broker or executing venue may step in and buy shares in the open market to complete the delivery. The seller is charged for the purchase, and any price difference between the original sale and the forced buy-in is borne by the seller.
How it works
Settlement for most U.S. equities occurs on a T+1 basis, meaning the seller must deliver shares one business day after the trade date. If a short seller fails to deliver, the buyer's broker may issue a buy-in notice. The seller's broker then purchases shares in the market, typically without the seller's consent, and debits the seller's account for the cost. If the buy-in price exceeds the original short sale price, the seller realizes the difference as an additional loss. If the buy-in price is lower, the seller may realize a smaller loss or even a gain, though forced buy-ins usually occur in stressed conditions where prices are rising.
Exchanges and FINRA publish threshold lists and failure-to-deliver data that help identify securities with persistent delivery problems. Repeated failures can lead to regulatory scrutiny and restrictions on further short selling in the affected security.
Worked example
A trader sells short 5,000 shares of LMN at $12.00 per share on Monday, expecting to borrow and deliver the shares by Tuesday's T+1 settlement. The trader's broker cannot locate the shares, and the lender of an earlier borrow recalls them. On Tuesday morning, LMN is trading at $14.50 because of positive news. To satisfy the delivery obligation, the broker executes a buy-in at $14.60, purchasing 5,000 shares and delivering them to the buyer.
The trader's account is debited $73,000 for the buy-in. The original short sale generated $60,000 in proceeds. The trader's realized loss on the trade is $13,000, plus any fees, compared with the $2,500 gain the trader would have realized if shares could have been covered at $11.50.
When traders use it
Traders do not initiate buy-ins voluntarily; they are imposed by brokers or clearing firms when delivery fails. Short sellers in hard-to-borrow or illiquid stocks face the highest risk, particularly around corporate actions, earnings, or when borrow supply dries up. A buy-in can occur even if the short position is profitable on a mark-to-market basis, because the inability to deliver shares forces a purchase at the current market price.
Traders monitor the FINRA threshold list and failure-to-deliver reports to identify stocks where buy-ins are more likely. A cluster of failures can signal that short covering or forced buying may create upward price pressure.
Check delivery risk and short interest data on the [most-shorted data page.]
Limitations and common misconceptions
A buy-in is not the same as a margin call. A margin call requires the depositor to add cash or securities; a buy-in is an actual transaction executed to satisfy a delivery obligation. Brokers are not required to notify the seller before executing a buy-in, though they often do so as a courtesy.
A buy-in does not necessarily mean the broker failed; it reflects a breakdown in the securities lending chain or a recall that cannot be backfilled. Traders should not assume that a short position can be held indefinitely if borrow is available; lenders can recall shares at any time, triggering a delivery requirement.