Mortgage rates get the headlines, but there's a less glamorous number quietly deciding whether you get the keys or the rejection letter: your debt-to-income ratio, or DTI.
Lenders use it to answer one blunt question — after you pay everyone else, is there enough left for a house?
Add up your minimum monthly debt payments: car loans, student loans, credit card minimums, personal loans, child support.
Divide that by your gross monthly income before taxes.
If you earn $6,000 a month and owe $2,100 in payments, your DTI is 35%.
Most conventional loans want that number at or below 43%, though many lenders prefer 36% or lower.
Go above 50% and you're essentially locked out of most mortgages, even with a stellar credit score and a fat down payment.
Government-backed loans are slightly more forgiving — FHA often allows up to around 50% with compensating factors.
The catch is that the cutoff isn't one clean national rule.
Fannie Mae's automated system can approve DTI up to 50% in some cases, but lenders layer on their own "overlays" that tighten the limit.
That's why two buyers with identical finances can get different answers from different banks.
What counts against you surprises people.
Student loans in deferment or income-based repayment still get counted, often at 1% of the balance or the actual payment, whichever the lender prefers.
A cosigned loan for a relative's car counts too, even if you never drive it.
Credit card minimums count, which is why paying down a card helps twice — it lowers both your DTI and your credit utilization.
The fastest levers to pull before applying: pay off or pay down installment loans, avoid financing a car in the six months before you house-hunt, and don't open new credit cards mid-process.
A raise or a side gig helps, but only if it's documented and likely to continue.
One more trap worth knowing: getting pre-approved isn't the finish line.
Lenders often recheck your finances days before closing.
Financing furniture for the new place after you're approved can sink the whole deal.
Keep your credit and bank accounts boring until the keys are in your hand. **The bottom line:** Your DTI matters more than most buyers realize, and it's one of the few mortgage factors you can genuinely improve in a few months.
Before you shop for homes, calculate the ratio, attack the smallest debts, and pause big purchases.
Final Thoughts
A little patience now can mean a much better loan later.