Your debt-to-income ratio, also known as your back-end ratio, tells you how much of your monthly salary is eaten up by all of your expenses, not just housing. Your expenses would include any recurring payment, such as your mortgage loan, car payment, student loan payment, credit card debt, and child support. Most lenders want your total monthly debts to account for no more than 36 percent of your monthly income. To determine your maximum affordable debt-to-income ratio, multiply your annual salary by .36 and divide the resulting figure by 12. For a $50,000 annual salary, the maximum amount of monthly debt obligations you'd be able to afford would be $1,500. Remember, that figure includes your mortgage payment and all other monthly debts.