In finance, margin is the collateral that a holder of a financial instrument has to deposit with a counterparty (most often their broker or an exchange) to cover some or all of the credit risk the holder poses for the counterparty. This risk can arise if the holder has done any of the following:

• Borrowed cash from the counterparty to buy financial instruments,
• Borrowed financial instruments to sell them short,
• Entered into a derivative contract.

The collateral for a margin account can be the cash deposited in the account or securities provided, and represents the funds available to the account holder for further share trading. On United States futures exchanges, margins were formerly called performance bonds. Most of the exchanges today use SPAN ("Standard Portfolio Analysis of Risk") methodology, which was developed by the Chicago Mercantile Exchange in 1988, for calculating margins for options and futures.