Free trade implies same interest rate... at least the same real interest rate. The difference in rates between your USD credit card debt, EUR Greek bonds, GBP s

Free trade implies same interest rate... at least the same real interest rate. The difference in rates between your USD credit card debt, EUR Greek bonds, GBP savings accounts, and anything else just boils down to overhead, inflation expectations, and risk. The actual time value of money part costs the same. It's the Law of One Price in action, and currency is pretty mobile and fungible. Heck, you'd see the same for BTC-based loans if the risk factor was low enough for sane people to consider offering them. (Of course, when you've got crazy government-imposed capital controls, like China or something, it's another story.)