Hi I am new to IB, and i have a problem understanding how to choose base currecy. I just don't understand why people would choose a base currecy other than the highest interest rate currecy (ie mexico). Well, maybe because of the instability of their political condition. People might as well choose the Aussie dollar as their base currecy since it pays a high interest and their country is pretty stable. What am i missing here? There is no downside for choosing Aussie even you trade solely the US market. All of your fund is in USD and there is no exchange rate risk. IB just convert your fund into Aussie dollar on paper at the end of the day and pay you a interest rate higher than the USD interest rate. I would really appreciate any comments from IB's user.