One rule of thumb to consider is that your mortgage payment shouldn't exceed more than a third of your monthly income. When you apply for a mortgage, your bank will calculate the loan amount you're eligible for based on your total monthly debts versus your pre-tax income. There's also the 28/36 rule. This rule goes a step further, recommending spending no more than 28% of your income on housing expenses and no more than 36% on your total debt (including car payments, student loans, credit cards, etc.)