Front-End vs. Back-End DTI: What Lenders Actually Check
The difference between front-end and back-end debt-to-income ratios, why lenders check both, and which one usually ends up limiting a mortgage.
Mortgage lenders don't use a single debt-to-income number — they check two, and the stricter one wins.
| Front-end DTI | Back-end DTI | |
|---|---|---|
| What it measures | Housing payment only | Housing payment + all other debts |
| Typical cap | ~28% | ~36% (conventional), higher for some programs |
| Affected by a car loan? | No | Yes |
| Affected by a raise? | Yes | Yes |
Why both exist
Front-end DTI answers "can this income support this house payment on its own?" Back-end DTI answers "can this income support this house payment on top of everything else this person already owes?" A borrower with no other debt and a borrower with heavy debt could have identical incomes and identical front-end ratios, but very different back-end ones — which is exactly the risk difference a lender cares about.
Which one usually binds
For borrowers with little or no existing debt, front-end DTI tends to be the limiting factor. For borrowers carrying car loans, student loans, or credit card balances, back-end DTI often becomes the tighter constraint — meaning paying down debt before house-hunting can raise the affordable price more than it might seem at first glance.
The House Affordability Calculator checks both automatically and tells you which one is actually limiting your result.