Debt-to-Income Ratio: How Lenders Actually Calculate It

DTI is the gatekeeper. Income gets you in the door, but your debt ratio decides how large a mortgage the underwriter signs off on. Here is the exact math and the moves before you apply.

Lenders do not care about your salary in isolation. They care about what is left after your existing obligations. That remaining margin determines your maximum mortgage payment. Most buyers learn this too late, after they have already applied and received a loan amount thousands below what they expected. Calculate yours now with our home affordability calculator to see the real number.

Front-End vs Back-End DTI

There are two ratios, and underwriters look at both:

Front-end DTI: Your housing payment (principal, interest, taxes, insurance, HOA) divided by gross monthly income. The classic rule is 28%, though FHA allows 31% and some automated approvals stretch it.
Back-end DTI: Housing payment plus all other minimum debt payments divided by gross income. The conservative threshold is 36%, with FHA reaching 43% to 50% depending on the file.

An Example: $90,000 Salary, Existing Debts

Gross monthly income: $7,500. Existing minimum payments: $650 car, $400 student loans, $150 credit cards. Total non-housing debt: $1,200.

Maximum back-end (36%): $7,500 x 0.36 = $2,700 total allowed

Minus existing debt: $2,700 - $1,200 = $2,100 left for housing

At 6.75%, 30-year fixed, that supports roughly a $325,000 loan

If the same borrower had no car or student loans, the housing allowance jumps to $2,700, supporting roughly a $415,000 loan. That is a $90,000 difference purely from existing debt.

What Counts Toward Debt

Only debts with 10 or more months of payments remaining are included. This includes auto loans, student loans, credit card minimums, personal loans, alimony, child support, and existing mortgages. It does not include utility bills, insurance premiums, rent (for the new application), or cell phone plans. If you are making extra payments on a debt and only the minimum is required, only the minimum is counted.

How to Improve Your DTI Before Applying

Pay revolving balances below 10%. Credit card minimums are calculated as a percentage of balance. A $3,000 balance might carry a $60 minimum. Zero it and that disappears from the ratio.

Do not open new credit. A new car loan six weeks before your mortgage application can drop your preapproval by $50,000.

Document side income. Two years of tax returns showing consistent freelance profit is enough for most lenders to add it to qualifying income. Even an extra $1,000 per month drops your DTI significantly.

Consider a 15% down payment. On conventional loans, lower loan-to-value ratios can trigger automated approval at higher DTIs because the lender risk drops. The rate improvement from 3% to 15% down is meaningful, and some lenders allow 43% back-end DTI where they would have capped a 5% borrower at 36%.

Run your exact numbers in our mortgage calculator and see what your DTI translates to in real purchasing power.