DTI Ratio: What Mortgage Lenders Actually Look At
Before a lender looks at your credit score, your down payment, or the house itself, they run one number: your debt-to-income ratio. It's the fastest filter for whether you can realistically carry a new mortgage payment on top of what you already owe.
Two ratios, not one
Lenders actually calculate DTI two different ways, and both matter:
- Front-end DTI — your proposed housing payment (principal, interest, taxes, insurance, HOA) divided by gross monthly income. Conventional lenders typically want this at or below 28%.
- Back-end DTI — your housing payment plus every other recurring debt, divided by gross monthly income. This is usually capped around 36% for the best rates, though many programs allow 43-50% with compensating factors.
(Definition source: Consumer Financial Protection Bureau.)
What actually counts as debt
Back-end DTI includes more than people expect: car loans, student loans, minimum credit card payments, personal loans, child support or alimony obligations, and payments on any other property you own. It does not typically include utilities, insurance premiums unrelated to housing, groceries, or subscriptions — recurring bills, yes, but not "debt" in the underwriting sense.
Why back-end DTI is the real ceiling
Two people can earn the same income and qualify for very different mortgage amounts purely based on existing debt. A $500/month student loan payment doesn't just cost you $500 — it can reduce your approved mortgage amount by well over $80,000, because that $500 is competing with your future housing payment for the same 36-43% ceiling.
How to actually lower your DTI before applying
Two levers move this number: increase income (harder, slower) or reduce debt payments (often faster). Paying off a car loan or a card with a large minimum payment can improve your DTI more than paying down a larger balance with a small minimum payment — underwriting cares about the monthly payment, not the total balance owed.
A DTI that "qualifies" isn't automatically comfortable
Just like the affordability ratios, a DTI that clears the lender's bar doesn't necessarily leave you room to save, invest, or absorb a job disruption. It's worth calculating both your front-end and back-end DTI honestly — including debts you might be tempted to leave out — before deciding what payment you're actually comfortable carrying, separate from what you'd be approved for.
How we verify this: figures on this page are computed from standard published formulas and checked against our own calculators. Assumptions are stated inline. Found an error? Let us know — see our editorial approach.