Hello,I have the following scenario/question around initial marginLet's say my portfolio contains a single futures contract X, which I clear on an exchange, and I put up Initial Margin (IM) calculated using some methodology (e.g. SPAN).A month later, I trade futures contract Y, so my portfolio contains both X and Y. Y does not offset X.When I clear the second futures contract, is the IM calculated on Y only, or is it calculated on the portfolio of X and Y together (with netting)?In addition, let's say the required IM calculated on X and Y together is lower than the required IM calculated on X originally (say, due to diversification benefit). Do I get to withdraw the excess IM currently posted with the clearing house?Thanks!

SPAN is calculated at the portfolio level. So the answer is yes. (You can withdraw margin if there is a partial offsetting of the risk of X by Y. A made up example: X= long crude, Y=short natural gas).