How mortgage lenders calculate home affordability
When underwriting a home mortgage, banks and mortgage companies do not look solely at your total annual income. They evaluate your Debt-to-Income (DTI) ratio to ensure that unexpected expenses or job disruptions do not push you into loan default.
The standard 28/36 qualifying DTI rule
Most conventional conforming mortgages (Fannie Mae and Freddie Mac) use the 28/36 guideline:
- Front-End Ratio (28%): Your total monthly housing expenses (Principal + Interest + Property Taxes + Homeowners Insurance, abbreviated PITI) should not exceed 28% of your gross monthly income.
- Back-End Ratio (36%): Your total monthly debt obligations (your PITI housing payment plus car payments, student loans, minimum credit card payments, and child support) should not exceed 36% of your gross monthly income.
Lenders calculate both ratios and cap your maximum loan amount at whichever limit is more restrictive.
Affordability comparison table across interest rates
The table below illustrates how changing mortgage interest rates affects maximum purchasing power for an $85,000 household income with $500 monthly debt and a $50,000 down payment:
| Mortgage Interest Rate | Max Home Price | Max Mortgage Loan | Monthly PITI Payment |
|---|---|---|---|
| 5.50% Fixed | $334,812 | $284,812 | $1,983 / mo |
| 6.00% Fixed | $316,845 | $266,845 | $1,983 / mo |
| 6.50% Fixed | $300,432 | $250,432 | $1,983 / mo |
| 7.00% Fixed | $285,398 | $235,398 | $1,983 / mo |
| 7.50% Fixed | $271,595 | $221,595 | $1,983 / mo |
Key ways to increase how much house you can afford
- Pay Off High-Interest Consumer Debt: Eliminating a $450/month car loan or credit card balance immediately frees up budget under the 36% back-end DTI cap, boosting your home buying power by over $70,000.
- Increase Your Down Payment: A larger down payment directly increases your purchase price dollar-for-dollar and avoids Private Mortgage Insurance (PMI) if you reach 20% equity.
- Shop for Lower Interest Rates: A 1.0% decrease in your mortgage rate increases your purchasing power by roughly 10% to 12% without increasing your monthly payment.
- Improve Your Credit Score: Borrowers with credit scores above 740 receive the lowest interest rates and lower PMI rates than borrowers in the mid-600s.
Frequently asked questions about home affordability
How much house can I afford on an $80,000 salary?
On an $80,000 salary with $400 in monthly debt and a $40,000 down payment at 6.5% interest, you can afford a home priced up to approximately $277,000 with a monthly PITI payment of $1,867.
What is the difference between this and a loan payment calculator?
A loan calculator calculates the monthly repayment on a specific borrowed dollar amount. This affordability calculator works in reverse: it takes your income and debts to determine the maximum safe purchase price you qualify to buy.
What is Private Mortgage Insurance (PMI)?
If you put down less than 20% on a conventional mortgage, lenders typically require PMI, which costs between 0.3% and 1.5% of the loan balance annually. Once you reach 20% equity through amortization or property appreciation, PMI can be cancelled.
Created and calculation-tested by Velour Trends · Updated 9 November 2026. Standard 28/36 underwriting guidelines verified. Report a calculation issue.