Mortgage lenders look at a lot of numbers before they approve a loan, but one figure carries more weight than most borrowers realize.
It's called the debt-to-income ratio, or DTI, and it compares what you owe each month to what you earn.
Get it wrong, and even a solid credit score might not save your offer.
Add up your monthly debt payments: car loan, student loans, minimum credit card payments, and any personal loans.
Divide that total by your gross monthly income, the amount before taxes come out.
The result is your DTI, expressed as a percentage.
A household bringing in $6,000 a month with $1,800 in debt payments sits at 30%.
Lenders traditionally prefer a DTI at or below 36%, with no more than 28% of that going toward housing.
But many conventional loans now allow ratios up to 43%, and some government-backed programs stretch higher with compensating factors like cash reserves or a strong credit history.
Cross those lines and you may still qualify, but expect more scrutiny and possibly a higher rate.
The trap is that most buyers calculate their ratio using the mortgage they want, not the one they can realistically get.
At today's rates, a $350,000 loan can run roughly $2,200 a month once you add taxes and insurance, depending on where you live.
Pair that with a $500 car payment and $200 in credit card minimums, and a household earning $7,000 a month lands near 41% — inside the range, but with little breathing room.
What counts against you might surprise you.
Lenders generally use the minimum payment on credit cards, not your actual balance, so a $50 minimum on a $4,000 balance only adds $50 to the calculation.
But they do count student loans, even ones on income-driven repayment plans, often at 1% of the balance or the documented payment.
Meanwhile, expenses like groceries, utilities, and streaming subscriptions don't factor in at all, which is why some borrowers feel stretched even after qualifying.
If your ratio is too high, you have a few practical moves.
Paying down a credit card can lower the minimum and shrink your DTI within a billing cycle.
Avoiding new car loans or financed furniture before you apply keeps the number clean.
A larger down payment reduces the loan amount and the monthly housing cost.
And in some cases, adding a co-borrower with steady income changes the math entirely.
One more thing worth knowing: DTI is not the same as your credit score, and paying your bills on time won't fix a ratio that's out of balance.
A perfect payment history with $900 in monthly debt payments still produces a high DTI if your income hasn't kept pace.
The smartest move is to run your own numbers before a lender does.
Pull your monthly debt payments, check your pay stubs, and see where you land.
That five-minute exercise can tell you whether you're ready to shop or whether a few months of paying down balances would put you in a stronger position. **Our take:** DTI is one of the few mortgage rules you can actually control, and most buyers ignore it until a denial letter forces the issue.
Knowing your ratio early turns a stressful guessing game into a straightforward plan.
Final Thoughts
Run the math now, and you'll walk into any lender's office already ahead.