When determining your ability to qualify for a mortgage, a lender takes a solid look at your *debt-to-income ratio. Based on this formula they can better determine what loan amount you can or cannot qualify for.
The percentage of your gross monthly income (before taxes) that you spend on debt.
This will include monthly housing costs (principal and interest, taxes, insurance, and homeowner’s association fees if applicable). It will also include your monthly consumer debt – (credit cards, student loans, installment debt, etc).