Mortgage calculator

Debt-to-Income Calculator

Divide your housing payment and your total monthly debts by your gross monthly income to get the two ratios lenders weigh alongside credit, reserves, and the property.

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Assumptions this tool makes

Income is gross monthly income — pay before taxes and deductions — because that is the basis lenders use for these ratios.
The housing payment you enter should be the full proposed payment: principal, interest, property tax, homeowners insurance, HOA dues, and mortgage insurance where it applies.
Other monthly debts are the minimum required payments on debts that appear on a credit report or in a file — car loans, student loans, credit card minimums, support obligations. Groceries, utilities, and subscriptions are not debts in this math.
The result is two divisions and nothing more. It is not an approval, a denial, or a program limit, and no single ratio decides a loan.

The formula

Front-end ratio = housing payment ÷ gross monthly income × 100. Back-end ratio = (housing payment + other monthly debts) ÷ gross monthly income × 100.

A worked example

Gross monthly income $12,500, proposed housing payment $4,200, other monthly debts $450.

Front-end ratio: $4,200 ÷ $12,500 × 100 = 33.6%.
Back-end ratio: ($4,200 + $450) ÷ $12,500 × 100 = $4,650 ÷ $12,500 × 100 = 37.2%.
The $450 of other debts adds 3.6 points to the back-end ratio: $450 ÷ $12,500 × 100 = 3.6.

Program benchmarks for context

For context only: on a conventional loan, Fannie Mae's automated underwriting system (Desktop Underwriter) caps the total — back-end — ratio at 50 percent, so a back-end ratio near or above that mark is where conventional files commonly fail, and manually underwritten conventional loans are capped lower. FHA sets its own benchmarks, including ratio benchmarks for manually underwritten files; the FHA loans page explains how FHA underwriting treats these ratios. An individual lender can set a tighter cap than either program allows, so treat these as context for your result, not as an approval line.

How to read your result

Work the denominator and the numerator separately: at $12,500 of monthly income, every $125 of monthly debt is exactly 1 point of back-end ratio.
If the back-end ratio is the obstacle, paying a debt off entirely helps more than paying it down, because the ratio counts the required monthly payment, not the balance.
If the front-end ratio is high but the back-end ratio is close behind it, housing cost itself is the pressure point — a lower price or a larger down payment moves both ratios at once.
Run the numbers with the full housing payment, including tax, insurance, and HOA dues. A principal-and-interest-only figure understates the front-end ratio on every California purchase.