"How much can I afford to pay for a house?" It's a question all hopeful homebuyers ask themselves. Coming up with a monthly payment that works for you might be easy -- simply subtract your monthly expenses from your gross monthly income. Unfortunately, that number might not align with the amount of money a bank will lend you. That's because banks and other lending institutions have a formula they often use to determine what you can afford: the 28/36 rule. WHAT IS THE 28/36 RULE?