Interactive Brokers is charging $4,332 maintenance margin for a position long 1 ES contract. Meanwhile, they are charging $6,456 on a position short 1 ES put. (Expiration May 20, strike 1975, value of put ~1 ES point). It doesn't make sense that shorting an out-of-the-money put would cost more in margin than being long an outright. (The numbers come from tests on their simulated trading platform, but I'm seeing similar numbers in a live account.) Anyone know what's happening there?
There is also a daily bias either on the long side or short side with regard to ES futures options. In other words the same position may have drastically different margins from day to day - depending on market conditions and direction. I've seen my margin change quite a bit during the afternoon reset on some days when the market doesn't move much - but the bias changes.
It's not a big deal for me because I don't really push the margin envelope. If I get some crazy high margin number, it might be 50% of what's available. Typically it's very low for me - but may push up a bit if I have overlapping weeks on. And I've been with them forever and don't really have much incentive to make a move.
Their margin requirements are not always the best in the industry though I do like their platform and cost. Margin sometimes handled worse than even ToS.