I trade through OptionsHouse. I do a lot of credit spreads, and many times after I put a credit spread on, I'll put on another credit spread on the other side of the market and effectively leg into an iron condor. When I put on the second leg of the iron condor, the order summary shows that no extra margin is required, which is correct (assuming the max risk of the 2nd leg is not greater than the max risk of the 1st leg). This is convenient because some brokerages don't do this. When I try to do it on Ameritrade they require separate margin. But anyway... When I take off one of the legs of the iron condor, it tells me that I don't have enough buying power to do so. This doesn't make sense to me since the margin should be the same for 1 or 2 legs of an iron condor (for simplicity's sake, let's assume the max risk on both legs is equal). Does anyone know why this is? OptionsHouse doesn't seem to know. I thought this might be a possible explanation... Is is possible that if I liquidate a leg that has a loss, then it creates a realized loss and hence a lower account balance where I now don't have enough money to cover the margin for the first leg?