Two requirements, one position
initial margin = what you need to open
maintenance margin = what you need to keep it open
Initial is set by the exchange and marked up by most brokers. Maintenance is lower — typically around 90% of initial — and dropping below it triggers a margin call.
Three ES contracts at a $14,300 initial requirement need $42,900. That figure has nothing to do with the value of the position, which at 5,200 points and a $50 multiplier is $780,000 of notional.
Margin is not risk, and the ratio is extreme here
The point holds in every market and is starkest in futures: margin is collateral, not the amount at risk. What can be lost is set by the stop.
But futures make the relationship easy to misjudge, because the leverage is so large. That $14,300 controls $780,000 of index exposure — around 55:1. A 2% move in the index is a $15,600 swing on one contract, which is more than the margin posted.
So the honest reading of a margin figure is not "this is what I am risking" but "this is how little of my capital is committed relative to what the position can do". The leverage calculator puts the same relationship in the form that decides survival.
The distance to a margin call, in points
This is the row that makes the page useful rather than arithmetical.
points to a margin call = (equity − maintenance × contracts) ÷ (multiplier × contracts)
A $13,500 account holding one ES contract at $13,000 maintenance has a $500 buffer — which is 10 points. Ten points on the S&P is an ordinary hour.
Put that next to your stop. If the stop is 15 points away, the broker's forced liquidation arrives before your exit does, and the position is closed at the market rather than at your level. The plan was never going to run.
That comparison — buffer against stop, in the same units — is the check worth doing before the position is opened rather than during it.
Requirements change, and they change at the worst time
Exchanges raise margin requirements in volatile conditions, and brokers raise them further and faster. The increase applies to positions already open.
This has a specific consequence: a position that comfortably met the requirement on Friday can breach it on Monday without the price moving at all. Any plan that only works at the current margin level has a dependency held by somebody else, and it is worth leaving enough free equity that a routine increase does not become an event.