Margin call

Margin level is equity divided by used margin, expressed as a percentage. As open losses erode equity the ratio falls, and crossing the broker's margin-call threshold — commonly 100% — blocks new positions and warns that action is required.

If the ratio keeps falling to the stop-out level, often 50%, the broker begins closing positions automatically. Because this happens during violent moves when spreads are widest, forced liquidation typically executes at some of the worst prices available.