DTI - Debt-To-Income ratio. This is the ratio that lenders use to determine how much of a borrower's income is going to his/her expenses. A "front-end" ratio shows how much is going towards housing expenses only. A "back-end" ratio shows how much is going towards housing expenses PLUS installment debt, child support, credit cards, etc. For example: a person making $4000 per month, with a $1000 house payment and $350 in other payments per month has a 25% front end ratio and a 33.75% back end ratio.