Mortgage Debt-to-Income Qualification Calculator
Estimates the maximum mortgage loan amount you can qualify for based on your income, existing debts, and standard lender DTI limits. Useful before you start house hunting.
About this calculator
Lenders evaluate affordability using the debt-to-income (DTI) ratio: total monthly debt obligations divided by gross monthly income. Most conventional loans require a back-end DTI below 43–45%, while FHA allows up to 50% in some cases. The 'loanType' input here represents the applicable DTI limit as a percentage. The maximum allowable monthly payment is: maxPayment = (grossIncome × DTI%) − monthlyDebts − propertyTax. This payment budget is then reverse-engineered using the amortization formula to find the maximum loan: L = maxPayment × [(1+r)ⁿ − 1] / [r × (1+r)ⁿ], where r = interestRate / 12 / 100 and n = 360 months. The result tells you how large a loan your income can support.
How to use
Gross income = $7,000/month, existing debts = $400, interest rate = 6.8%, DTI limit = 43%, property tax = $250/month. Max allowable payment = ($7,000 × 0.43) − $400 − $250 = $3,010 − $650 = $2,360. Monthly rate r = 6.8/100/12 = 0.005667. n = 360. Max loan = $2,360 × [(1.005667)³⁶⁰ − 1] / [0.005667 × (1.005667)³⁶⁰] ≈ $355,000. Add your down payment to find your maximum purchase price.
Frequently asked questions
What debt-to-income ratio do I need to qualify for a mortgage?
Most conventional lenders require a back-end DTI (all monthly debts including the new mortgage) at or below 43–45%. Fannie Mae's automated underwriting will sometimes approve loans up to 50% DTI for borrowers with strong compensating factors such as large cash reserves or excellent credit. FHA loans allow up to 50% DTI more readily. The lower your DTI, the more likely you are to receive the best interest rates and terms.
How do monthly debt payments affect how much mortgage I can qualify for?
Every dollar of existing monthly debt — car loans, student loans, credit card minimums — directly reduces the payment budget available for a mortgage. For example, a $400/month car payment on a $7,000 income at a 43% DTI reduces your available mortgage payment by $400, which can cut your maximum loan amount by $50,000 or more. Paying down or eliminating debts before applying can significantly increase your purchasing power. Even removing a small recurring debt improves your qualification ceiling.
Why does the lender use gross income instead of take-home pay when calculating DTI?
Lenders use gross (pre-tax) income because it is a consistent, verifiable figure documented on pay stubs, W-2s, and tax returns. Take-home pay varies widely based on withholding elections, retirement contributions, and benefit deductions that the borrower controls and can change. Using gross income creates a standardized comparison across all applicants. It does mean your actual budget will feel tighter than the DTI numbers suggest, since you pay taxes and other withholdings from the gross figure before any mortgage payment is made.