Mortgage rates have finally slipped from their recent peaks, and that has millions of Americans thinking about buying or refinancing.
But there's a number that matters just as much as the rate on the loan—and most buyers don't check it until a lender delivers bad news.
It's called the debt-to-income ratio, or DTI.
It compares what you owe each month to what you earn, and it has quietly become one of the biggest gatekeepers in the housing market.
Add up your monthly debt payments: car loans, student loans, minimum credit card payments, personal loans, and any mortgage you already carry.
Divide that total by your gross monthly income—what you earn before taxes.
The result is your DTI, expressed as a percentage.
Lenders draw hard lines around that figure.
For most conventional loans backed by Fannie Mae and Freddie Mac, the maximum DTI is 45%—though some borrowers can push to 50% if they have strong credit and cash reserves.
Federal Housing Administration loans often allow up to 43%, and some lenders stretch to 50% with compensating factors.
Cross those thresholds and the answer is usually no, regardless of how much you have saved for a down payment.
A 20% down payment won't rescue an application with a 55% DTI.
It moves every time you take on new debt, and it can swing fast.
Financing a $32,000 truck at today's average auto loan rate adds roughly $600 a month.
On a $6,000 monthly income, that single decision can push someone from a comfortable 36% DTI to a disqualifying 46% overnight.
That's why mortgage advisors tell buyers to freeze major purchases during the home-shopping process.
A new car, a furniture financing plan, or even a store card opened at checkout can sink a loan that was already approved.
There's another wrinkle: the debt side isn't always what you'd expect.
Student loans in deferment or income-driven repayment still count, often at 1% of the balance or the scheduled payment, whichever is higher.
Even a co-signed loan for a relative's car lands on your DTI, whether or not you make the payments.
If your ratio is too high, you have a few levers.
Paying off a small installment loan can drop your DTI by several points quickly.
Paying down credit card balances helps, though it's the minimum payment that counts, not the balance.
Increasing your income—a raise, a side gig, a second borrower on the application—can move the needle too.
For refinancers, DTI works a bit differently.
Rate-and-term refinances often allow higher ratios than purchases, but cash-out refinances are scrutinized harder because you're adding to your loan balance.
One more thing worth knowing: DTI is not the same as your credit score.
A borrower with a 780 score and a 48% DTI can be turned down while someone with a 680 score and a 35% DTI sails through.
Lenders weigh both, but the ratio is often the deal-breaker.
Before you tour a single open house, run the numbers yourself.
Add up your debts, divide by your income, and see where you stand.
If you're close to the line, fix it before a lender does the math for you.
Our take: DTI is the most overlooked number in American homebuying, and it's the one most likely to cost you a house you can actually afford.
Final Thoughts
Check it early, keep it low, and don't finance anything with wheels until the keys to the house are in your hand.