Margin call

In finance, margin is collateral that the 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:

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.

A margin account is a loan account by a share trader with a broker which can be used for share trading. The funds available under the margin loan are determined by the broker based on the securities owned and provided by the trader, which act as collateral over the loan. The broker usually has the right to change the percentage of the value of each security it will allow towards further advances to the trader, and may consequently make a margin call if the balance available falls below the amount actually utilised. In any event, the broker will usually charge interest, and other fees, on the amount drawn on the margin account.

If the cash balance of a margin account is negative, the amount is owed to the broker, and usually attracts interest. If the cash balance is positive, the money is available to the account holder to reinvest, or may be withdrawn by the holder or left in the account and may earn interest. In terms of futures and cleared derivatives, the margin balance would refer to the total value of collateral pledged to the CCP (Central Counterparty Clearing) and or futures commission merchants.

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Wikipedia