Last week, we discussed some basics about shopping for a mortgage. After a lender pre-approves you for a mortgage, you must prove to the lender that you can repay the loan amount. The lender will calculate your total monthly housing costs and your total debt load. It will then calculate your gross debt service ratio and your total debt service ratio (more about these below). If these calculations show that you can pay your housing costs and your additional debts, you will probably get your mortgage.