Maintenance margin
The collateral level below which a position counts as underfunded and becomes liable to closure.
How to read the number
While free funds cover that level the position lives its own life; breaching it gives the broker the right to close it without the holder's consent.
When the metric lies
The level is derived from collateral that the exchange raises in step with volatility. The requirement grows without the holder trading at all, and does so on the day the market is against them.
Also known as: minimum margin level