How to calculate % profit in forex? -

I ve seen a service which reported approximately $50,000 profit for the last month. They say their performance is based on 5 Lots trade size. I know one lot is 100,000, so does it mean they have made 10% profit for that month? It really depends on what they are trading. For example 5 British pound contracts require initial margin of $7500. So your investment could be that limited if you trade every move correctly which is impossible. Any position at the close of trading is marked to the market and either generates excess margin (profit) or requires additional capital (loss). Won t they tell you what the return is?