Data used to decide whether a potential borrower qualifies for a mortgage. Lenders compare a borrower's monthly income to the proposed monthly mortgage expenses to decide whether the borrower is creditworthy. A "front" or "top" ratio reflects the borrower's monthly housing costs as a percentage of monthly income. This includes mortgage insurance fees, taxes, and principal. A "bottom" or "back" ratio reflects the sum of monthly housing costs and all other monthly debt.