Your total monthly debt obligations (housing + car + student loans + credit cards + child support) divided by gross monthly income. The number most lenders care about most.
Back-end DTI is the comprehensive debt picture. It adds all your monthly debt payments — the proposed mortgage, plus car loans, student loans, minimum credit card payments, child support, alimony, and any other recurring debt — then divides by your gross monthly income.
This is the number that drives most underwriting decisions. Common caps: 43-45% for conforming conventional loans, with some flexibility up to 50% with compensating factors. FHA can go up to 56-57% with strong residual income.
One nuance: not every monthly payment counts. Utilities, groceries, gas, daycare — those are living expenses, not debt. Only credit-reported obligations get added to back-end DTI.
Example
You earn $8,000/month gross. Mortgage PITI $2,500 + car $400 + student loan $300 + credit card minimum $150 = $3,350. Back-end DTI = $3,350 ÷ $8,000 = 41.9%. Right at the conforming threshold.
Formula
Back-end DTI = (Total monthly debt obligations ÷ Gross monthly income) × 100
Also known as
back DTI, bottom ratio, total DTI