I would just like to verify if I understood the IB web page correctly. If I traded crosses like GBP/JPY or EUR/GBP, and my account is in USD, is the margin required additive, e.g., for GBP/JPY, my margin comes from the conversion of GBP to USD plus JPY to USD (with commensurate leverage)? I would just like to understand why, at 50% leverage, 17500 units of GBP/JPY has a margin of 4698.99 at IB whereas the same order has a margin of 652.89 at OANDA (where basis of margin computation is just from GBP/USD)? I am using demos for both brokers. I sense I am misunderstanding something here?