Seems IG takes 0.5% profit at sell and buy time and exchange rate fluctuates at sell and buy times too. I don't know if IG allow to keep your fund in USD , trade in USD and keep profit in USD at convert at your discretion to avoid losing at each trade. My current understanding is , if we make 5% profit on a trade and USD/GBP fluctuate in your benefit by 1% you almost make 5% profit , since 1% IG conversion rate is covered but if exchange rate fluctuates against your benefit by 4% , your 5% profit is gone through 1% IG and 4% FX rate. IF you find out how to set multi currency , please let us know.