The truth is that a large portion of payday customers end up in dire financial straits because of these seemingly innocuous loans. Here’s what happens. The average payday loan charges a fee of about $15 for every $100 borrowed. That might sound like an interest rate of 15%, but that’s the fee for a two-week loan. On an annualized basis—which is how most people think about interest rates, or should—that translates into a rate of 391%.