DTI (debt-to-income ratio) is the most common qualification metric in mortgage underwriting. Most MLOs know the back-end DTI -- total monthly obligations divided by gross monthly income. Fewer understand that front-end DTI (housing expense only) is also evaluated by some programs and that automated underwriting systems weight both ratios differently depending on the loan type and borrower profile.
Front-End DTI Definition and Calculation
Front-end DTI (also called the housing ratio) divides the total housing payment -- PITIA (principal, interest, taxes, insurance, and any HOA dues or MIP) -- by gross monthly income. A borrower with a $2,800 housing payment and $8,000 gross monthly income has a 35% front-end DTI. FHA guidelines reference a 31% front-end DTI threshold, though DU and LP can approve higher ratios with compensating factors. Conventional loans do not have a separate front-end DTI limit published in the selling guides.
Back-End DTI Definition and Calculation
Back-end DTI divides all monthly debt obligations (housing payment plus minimum payments on all installment and revolving debt) by gross monthly income. The back-end ratio is the primary qualification benchmark. Standard back-end limits: FHA manual underwrite 43%, FHA with AUS approval can go higher with compensating factors, conventional per DU/LP up to 50% in some scenarios. VA and USDA use back-end DTI but also evaluate residual income as a secondary underwriting layer.
When Both Ratios Matter
- ✦FHA manual underwriting: both 31% front-end and 43% back-end are hard caps unless compensating factors documented
- ✦FHA AUS: front-end above 31% is acceptable with AUS approval and documented compensating factors
- ✦USDA: targets 29% front-end and 41% back-end; can go higher with GUS approval
- ✦VA: no front-end cap; back-end DTI is secondary to residual income in VA underwriting
- ✦Conventional: DU/LP do not separately flag front-end DTI; back-end is the primary constraint
Aria can calculate both front-end and back-end DTI for any income and liability profile and confirm which program allows the resulting ratios. Ask at vicariointel.com.
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