Mortgage lenders have a number they rarely put on the marketing brochures: your debt-to-income ratio.
It's the single biggest gatekeeper between you and a home loan, and it has quietly gotten harder to clear.
Your DTI is all your monthly debt payments divided by your gross monthly income.
That includes the prospective mortgage, plus car loans, student loans, minimum credit card payments, and personal loans.
If you earn $7,000 a month and owe $2,100 across everything, your DTI is 30%.
The magic threshold most conventional lenders follow is 43%.
Under the Qualified Mortgage rules, borrowers generally need a DTI at or below that line to get the safest, most standard loan terms.
Cross it, and you're pushed into pricier products, extra scrutiny, or a flat rejection.
The catch is that the math cuts deeper than most buyers expect.
Lenders calculate your future housing payment using the full principal, interest, property taxes, and insurance — not the number a real estate agent casually tosses out.
A $400,000 loan at today's rates can carry a monthly payment hundreds of dollars above what a buyer mentally budgeted for.
The 28/36 guideline is the older, stricter cousin.
It suggests keeping housing costs under 28% of gross income and total debt under 36%.
Plenty of buyers blow past both and still get approved, but they often end up house-poor — paying the mortgage but nothing else.
Self-employed workers, gig drivers, and commission earners get hit hardest.
Lenders average two years of tax returns, and every write-off that lowers your taxable income also lowers the income they'll count.
A freelancer who legitimately earns $90,000 but deducts aggressively can look like a $60,000 borrower on paper.
Even if you pay cards in full each month, lenders typically count 1% to 5% of the balance as a monthly obligation.
Carrying $12,000 across three cards could add $240 to $600 to your calculated monthly debt — enough to swing a borderline application.
Paying down revolving balances before applying can move your DTI more than shopping for a slightly better rate.
So can delaying a car purchase, refinancing a student loan to a lower payment, or adding a co-borrower with clean finances.
Buyers should also run the number themselves before talking to a lender.
Add up every minimum payment, estimate taxes and insurance for the specific property, and divide by gross income.
If the result lands near 43%, there's little room for a bidding war, a rate bump, or a surprise HOA fee.
One more thing worth knowing: the 43% line isn't a law.
Some lenders approve DTIs into the high 40s with compensating factors like large cash reserves or a long history of on-time payments.
But those loans often come with higher rates, and they leave zero margin if a job changes or a roof fails. **Our take:** DTI is less a rule than a mirror — it shows whether a mortgage would stretch you thin before a lender ever says no.
Run your own math first, and treat 43% as a ceiling to stay well under, not a target to hit.
Final Thoughts
The best mortgage is the one you can still afford after the closing paperwork is filed.