The front-end ratio is your total housing payment (principal + interest + taxes + insurance + HOA + PMI) divided by your gross monthly income. It's a subset of the back-end DTI that isolates how much of your income housing alone consumes.
There's no industry-standard front-end cap — most lenders look at back-end DTI for the hard limit — but a front-end above 35–38% is a warning sign that you may be house-poor. The classic rule of thumb is 28%.
Two borrowers with the same back-end DTI can have very different front-end ratios. A borrower with a $4,000 mortgage and $500 in other debt is in better shape than one with a $2,500 mortgage and $2,000 in other debt, even though both ratios add up the same.