Home Affordability Calculator
The 28/36 debt-to-income (DTI) rule is the benchmark lenders use to evaluate how much mortgage you can comfortably afford. Your total housing costs (principal, interest, taxes, and insurance) should not exceed 28% of your gross monthly income, and all your monthly debt payments combined should not exceed 36%. This calculator applies both limits to determine the maximum monthly housing payment and maximum loan amount you qualify for, then works backward to estimate your maximum home purchase price based on your down payment.
Home affordability formula
Front-end max housing = Gross Monthly Income * 0.28
Back-end max housing = Gross Monthly Income * 0.36 - Other Debts
Binding max housing = min(front-end, back-end)
Max P+I = Binding max housing - Tax and Insurance
Max Loan = Max P+I / r * (1 - (1+r)^-n)
Max Price = Max Loan / (1 - Down Payment %)
Where r is the monthly interest rate (annual / 12 / 100) and n is total monthly payments. The binding limit is the lower of the two DTI constraints.
Understanding the two DTI limits
- The 28% front-end limit applies only to housing costs (PITI).
- The 36% back-end limit applies to all debt payments including housing, auto, student loans, and credit cards.
- If you carry significant non-housing debt, the back-end limit is usually the binding constraint.
- Conventional loans backed by Fannie Mae may allow a back-end DTI up to 45% or 50% with compensating factors.
- Property taxes and insurance vary significantly by location; update those inputs with your local estimates.
Home affordability: frequently asked questions
What is the 28/36 rule?
The 28/36 rule is a guideline used by lenders and financial planners. Your housing costs (PITI: principal, interest, taxes, insurance) should not exceed 28% of your gross monthly income (front-end DTI), and your total debt payments should not exceed 36% of gross monthly income (back-end DTI).
What does PITI stand for?
PITI stands for Principal, Interest, Taxes, and Insurance. It is the total monthly cost of owning a home, including the mortgage payment, property taxes divided by 12, and homeowner's insurance divided by 12. PMI is also included if applicable.
Do all lenders use the 28/36 rule?
Many conventional lenders use it as a guideline, but actual limits vary. FHA loans allow a front-end DTI of up to 31% and back-end of 43%. VA loans focus on residual income rather than strict DTI. Fannie Mae and Freddie Mac allow back-end DTI up to 45% or 50% with strong compensating factors.
What counts as monthly debt for the back-end DTI?
Back-end DTI includes all required monthly debt payments: housing PITI, minimum credit card payments, auto loan payments, student loan payments, personal loan payments, and any other recurring debt obligations. It excludes utilities, groceries, and discretionary spending.
Should I borrow the maximum amount a lender will approve?
Not necessarily. Lender approval is based on minimum qualification standards. Your personal budget, savings goals, job stability, and other financial priorities may lead you to choose a more conservative purchase price than the maximum you qualify for.
Official sources
- Consumer Financial Protection Bureau: What is a debt-to-income ratio?
- HUD: Buying a Home.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.