03-26-2018 End of day posting. Going to try and explain what to watch out for when trading futures. One thing to do every 15 mins prior to the futures market close is compute your own equity/initial margin ratio and ensure that it is beneath the brokers %, AMPfutures is at 80%, tradovate is 90% and Gain Capital Futures is at 95%. The top would be with Gain Capital Futures in case you are a position trader since this means you can ride out anything, even Friday's huge move.
Equity/initial margin = net liquid value(account balance ( /-) unrealized profit or loss)/(all initial margin requirement). Most brokers will not care about the maintenance margin and will continue to do the calculation of risk based from initial margin.
Here is how futures brokers get you, they inform you day trading margin for sp500 is 500, the trade says if you want to hold it will cost $6,380. You finance the account for $5k and you long 1 contract of this sp500, you are up $750 bucks unrealized, you want to hold overnight since you know it will go up more. However, end of the day your account maintains $0, why is that you wonder? Because your equity/initial margin is above any of those brokers risk ratio.
In one of my accounts they shut 3 of my trades, I got angry because they ought to have the decency to call me to put more money in. Either way I'm up by a lot and that account just suffered 3k loss.