The cross margining system on BitMEX shares unrealised PnL between positions, locks only the maintenance margin in position margin, liquidates all cross margin positions simultaneously, and allows unrealised PnL to be used as margin for derivatives positions only. Realised PnL can be withdrawn, transferred, or used for Spot and Convert trading.
What Are the Key Characteristics of Cross Margin?
The cross margining system on BitMEX operates under four defining rules that govern how margin, PnL, and liquidation interact across your positions.
Unrealised PnL sharing. Unrealised PnL can be shared between positions using cross margin. A profitable position supports a losing one by contributing its unrealised gains to the overall margin pool. This reduces the likelihood of liquidation on individual positions.
Maintenance margin locking. Only the maintenance margin is locked in position margin. This means the system holds the minimum required amount, leaving the rest of your balance available for other activities such as opening new positions or placing orders.
Simultaneous liquidation. All cross margin positions for an account are liquidated at the same time. If losses across your positions exhaust your available margin, the Liquidation Engine closes every cross margin position at once. There is no selective liquidation of individual positions.
Unrealised PnL restrictions. Unrealised PnL can be used as margin for derivatives positions. However, only realised PnL can be withdrawn, transferred, or used to trade Spot or Convert. This distinction is important: until you close a position and lock in your profit, those gains cannot leave the derivatives margin pool.
How Does Unrealised PnL Affect Your Cross Margin Positions?
Unrealised PnL plays a dual role in the cross margin system. It increases your available margin for derivatives positions, but it cannot be accessed for non-derivatives activities.
If you hold a profitable XBTUSD position with 0.5 BTC in unrealised gain, that 0.5 BTC can support a new or existing ETHUSD position. But you cannot withdraw, transfer, or use it for Spot trading until you close the XBTUSD position and realise the gain.
This rule exists to protect the margin pool. Unrealised gains can reverse if the market moves against you. Allowing withdrawal of unrealised PnL would create the risk of insufficient margin for open positions.