It stands for additional margin; the amount of money that is collected from market participants with substantial or concentrated positions against a central counterparty (CCP) or in response to adverse information on a participant’s financial position. Additional margin is paid as an addition to the initial margin (IM) in order to cover a potential fall in the value of a position on the following trading day.

It is part of the different types of margin, literally: initial, variation and additional margin. All such types constitute the so-called total margin.

Additional margin represents all margins imposed on both long and short positions over and above the other margins.