"Intraday Initial margin $1,406. Assuming sp500 is at 1100. Does that mean I need $55000 + $1,406 to just start trade 1 e-mini sp500 contract?" - No, it means your broker allows you to trade 1 contract for $1406 during the day session. The broker takes the risk basically that you will not fall asleep or leave your computer and have a huge drawdown. My broker resets the margin at 15 minutes prior to closing or 4 pm ET. Some brokers even allow $500 day trader margin.