In every fx transaction, you are simultaneously buying one currency and selling another. Since every currency in the world is attached with an interest rate set by the
central bank of that currency’s country, you are obligated to pay the interest on the currency that you have sold, but you also have the privilege of earning interest on the currency that you have bought. For example, assume that New Zealand has an interest rate of 8% (800
basis points) and that Japan has an interest rate of 0.5% (50 basis points). If you decide to go long NZD/JPY, you will earn 800 basis points in annualized interest, but have to pay 50 basis points for a net return of 7.5% or 750 basis points.