IBKR calculates the amount of Excess Liquidity (margin excess) in your Margin account in real time. If your Excess Liquidity balance is less than zero, we will liquidate positions in your account to bring the Excess Liquidity balance up to at least zero.
Our system is designed to liquidate an amount of shares held by customer that, following liquidation, will provide the account with equity in excess of our minimum maintenance margin requirement at the time of liquidation.
You can use the following calculation to determine how much stock equity we may liquidate in your Margin account to bring your Excess Liquidity balance back to zero. Note the following calculation applies only to stocks
Liquidation Amount = (Excess Liquidity Deficit * 4)
Additional information is available on the Margin Education Center web page in the Securities Margin Calculations section