Debt-to-income ratio calculator.

How DTI is calculated

Fannie Mae defines the DTI ratio as total monthly obligations divided by total monthly income. Back-end DTI = (housing payment + all other monthly debts) / gross monthly income. Front-end DTI = housing payment / gross monthly income. For a home you will live in, Fannie Mae counts the full PITIA: principal, interest, taxes, insurance and association dues.

Worked example

Gross income is $6,000 a month. The proposed housing payment is $1,800 and other debts are $650 (a $350 car loan, $225 of student loans and a $75 card minimum). Front-end DTI is 1,800 / 6,000 = 30.0%. Back-end DTI is (1,800 + 650) / 6,000 = 40.8%. That is above 36% but within 45%, so a manually underwritten conventional loan would need the credit score and reserves in Fannie Mae's Eligibility Matrix, while a DU-underwritten file is under its 50% maximum. These are the default values in the form above.

Benchmarks and sources

Fannie Mae's maximum total DTI is 36% for manually underwritten loans, extendable to 45% with the required credit score and reserves, and 50% for loans underwritten through DU. Exceptions exist (for example cash-out refinances and borrowers without a credit score), and for government loans lenders follow each agency's rules, so FHA, VA and USDA limits differ. Source: Fannie Mae Selling Guide B3-6-02, Debt-to-Income Ratios (Announcement SEL-2025-02, April 2, 2025; checked September 30, 2026). The front-end figure is shown for reference; the limits above apply to the total ratio. Weighing a cash-out refinance or home equity loan? Try the HELOC calculator and the mortgage affordability calculator.

FAQ

What is a good debt-to-income ratio for a mortgage?

For Fannie Mae, a manually underwritten loan has a 36% total DTI maximum, which can stretch to 45% if the borrower meets the credit score and reserve requirements in the Eligibility Matrix. Loans run through Desktop Underwriter (DU) can go to 50%. Lower is better, and your lender decides.

What is the difference between front-end and back-end DTI?

Front-end DTI counts only the housing payment (principal, interest, taxes, insurance and any association dues) divided by gross monthly income. Back-end DTI adds every other monthly debt payment. The Fannie Mae limits above apply to the total (back-end) ratio.

Do FHA, VA and USDA use the same limits?

No. Fannie Mae's guide says lenders must follow the requirements of the respective agency for government loans, and lenders often add their own overlays. Treat the 36%, 45% and 50% lines here as conventional-loan benchmarks, not a promise of approval.

What counts as a monthly debt?

Fannie Mae counts the housing payment, installment loan payments (car, student, personal) that run beyond ten months, revolving card payments at the minimum due, lease payments, court-ordered alimony or child support, and other recurring obligations. Groceries, utilities and insurance you do not escrow are not debts.

How do a car loan or HELOC change my DTI?

A new car payment is added to your other debts. A HELOC payment is added to your housing payment, since it is secured by your home. Pick the loan type above and enter the new payment to see the change in both ratios.

This tool is a planning estimate, not a lending decision or financial advice. Lenders verify income and debts, apply their own overlays and may calculate payments differently. Everything runs in your browser; nothing you enter is sent anywhere.