How the debt-to-income ratio works
DTI is the single number lenders use to answer one question: how much of this person's income is already spoken for? The version that decides most approvals is the back-end ratio — all monthly debt payments divided by gross (pre-tax) monthly income. The front-end ratio counts housing alone. Two benchmarks do most of the work: the classic 28/36 rule (housing under 28% of income, all debts under 36%) marks the conventional comfort zone, and 43% is the back-end ceiling from the original qualified-mortgage rule — technically replaced by a price-based test in 2021, but still the number most lenders quote. One detail people miss: lenders use your credit card minimum payments, not your balances. A $8,000 balance with a $160 minimum counts as $160.
The formula
Gross monthly income is what you earn before taxes and deductions — annual salary divided by 12, or use our hourly to salary calculator if you're paid by the hour. Take-home pay is the wrong number here; every lender benchmark is quoted against gross. (Curious what taxes actually leave you? That's the income tax calculator's job.)
Worked example
Income $6,000/mo gross. Debts: rent $1,500, car $400, student loans $250, card minimums $120 — total $2,270.
Back-end DTI = 2,270 ÷ 6,000 × 100 = 37.8% — past the 36% comfort zone, under the 43% ceiling. Front-end = 1,500 ÷ 6,000 = 25%, comfortably under 28.
At this income, 36% allows $2,160 of monthly debt — $110 over. Alternatively, these debts hit 36% at $6,305.56 of monthly income.
What counts — and what doesn't
Only recurring debt obligations go in the numerator: rent or the full mortgage payment (with taxes and insurance — see the mortgage calculator for the whole PITI picture), car loans and leases, student loans, credit card minimums, personal loans, and court-ordered payments like child support or alimony. What does not count surprises people: utilities, groceries, gas, health and car insurance premiums, phone plans, daycare, subscriptions. You can spend $2,000 a month on living expenses and it won't move your DTI an inch — which is exactly why a "good" DTI doesn't automatically mean an affordable life, and why lenders look at credit score and reserves too.
How to move the number
The math gives you two levers. Shrinking the numerator works best when you kill an entire payment: paying off a $6,000 car loan with a $400 payment cuts the example's DTI by 6.7 points, while putting that same $6,000 toward a mortgage balance changes the payment — and the DTI — not at all. The car payment is the classic lever: it's often the largest non-housing line, and it ends. Growing the denominator is just as legitimate: a raise, a documented second income, or a co-borrower's income all count. What doesn't work: paying down credit card balances only nudges the minimums, and moving debt between cards changes nothing. If you're prepping for a mortgage application, the order of operations is usually: no new car loan, retire the smallest full payments, then apply.