Mortgage lenders rarely lead with the number that actually runs the show.
It isn't your credit score, and it isn't your down payment.
It's your debt-to-income ratio, or DTI — and it's quietly setting the ceiling on what you're allowed to borrow.
Add up every monthly debt payment: car loans, student loans, minimum credit card payments, personal loans, plus the mortgage you're hoping to get.
Divide that total by your gross monthly income before taxes.
That percentage is your DTI, and lenders treat it as a snapshot of how stretched you already are.
The magic number most conventional loans aim for is 36%.
Go above that and you're in "qualified mortgage" territory, where lenders start asking harder questions.
Push past 43% and many conventional loans simply close the door, though some government-backed programs like FHA and VA allow higher ratios with compensating factors.
What counts as income matters as much as what counts as debt.
Lenders will usually let you count base salary, consistent overtime, bonuses with a two-year history, and even alimony or child support you receive.
They generally won't count side gigs unless the paperwork shows a steady track record.
New graduates with big loan balances and modest starting salaries often discover their ratio is worse than they expected.
The 28/36 rule is the old-school shorthand: keep housing costs under 28% of gross income and total debt under 36%.
In today's market, where the median home price keeps climbing and mortgage rates hover well above the lows of 2020 and 2021, that rule feels almost nostalgic.
A household earning $80,000 a year would need to keep total monthly debt payments under $2,400 to hit 36% — and that includes the new mortgage.
Minimum payments on revolving balances count against you even if you pay them off monthly.
Carrying a $10,000 balance at a typical 22% APR means a minimum payment near $250, and that single line item can knock tens of thousands off your borrowing power.
Paying down cards before applying is often the fastest way to raise your ceiling.
Paying off the smallest balances first frees up monthly cash flow and shrinks your ratio quickly.
Avoiding new car loans and financing furniture before a home purchase keeps the math clean.
Saving for a bigger down payment helps indirectly by reducing the loan amount, which lowers the projected mortgage payment in the calculation.
One caution: don't assume pre-approval means final approval.
Underwriters recheck your finances before closing, and a new credit card opened during house hunting can blow up a deal.
Keep your credit profile frozen in place from application to closing.
Run your own numbers before a lender does.
Add up your minimum payments, divide by your monthly gross pay, and see where you land.
If you're near 43%, you have homework to do — and it's better to find out now than after you've fallen in love with a house.
The uncomfortable truth is that DTI rewards people who already have room to breathe and punishes those juggling car notes and card balances.
It's a blunt instrument, but it's the one lenders use.
Final Thoughts
Knowing your number early gives you time to change it before it changes your plans.