House Buying Budget Calculator
Find the maximum home price you can afford based on your income, debts, down payment, interest rate, and property taxes. Use it when beginning your home search to set a realistic price range.
About this calculator
This calculator applies the 28% front-end debt-to-income rule used by most mortgage lenders: your monthly housing costs (principal, interest, and property tax) should not exceed 28% of gross monthly income. The maximum affordable monthly payment is: maxPayment = (annualIncome / 12 × 0.28) − monthlyDebts. From that payment, the calculator back-solves for loan amount using the standard mortgage payment formula: P = payment / (r(1+r)ⁿ / ((1+r)ⁿ − 1) + taxRate/12), where r = monthly interest rate and n = total months. Because your down payment covers part of the purchase price, the maximum home price scales up: homePrice = loanAmount × (100 / (100 − downPaymentPercent)). Property tax is included as a recurring monthly cost that reduces the portion of your payment available for principal and interest. This approach mirrors how an underwriter evaluates your application.
How to use
Inputs: $120,000 annual income, $500 monthly debts, 20% down payment, 7% interest rate, 30-year loan, 1.2% property tax rate. Step 1 — max monthly housing payment: ($120,000 / 12 × 0.28) − $500 = $2,800 − $500 = $2,300. Step 2 — monthly rate r = 0.07/12 ≈ 0.005833; n = 360. Step 3 — mortgage factor: 0.005833 × (1.005833)^360 / ((1.005833)^360 − 1) ≈ 0.006653. Step 4 — add monthly tax rate: 0.012/12 = 0.001. Step 5 — loan amount: $2,300 / (0.006653 + 0.001) ≈ $300,457. Step 6 — home price: $300,457 × (100/80) ≈ $375,571.
Frequently asked questions
How does my debt-to-income ratio affect how much house I can afford?
Lenders use two DTI thresholds: the front-end ratio (housing costs ÷ gross income) capped at 28%, and the back-end ratio (all debts ÷ gross income) capped at 36–43% depending on the loan type. High existing debts — car loans, student loans, credit cards — directly reduce the monthly payment available for a mortgage. For every $100 in monthly debt you eliminate before applying, you may qualify for roughly $13,000–$15,000 more in home price at a 7% rate on a 30-year loan. Paying down debt before house-hunting is one of the most effective ways to raise your price ceiling.
What is the minimum down payment needed to buy a house and avoid PMI?
Conventional loans require a 20% down payment to avoid private mortgage insurance (PMI), which typically costs 0.5–1.5% of the loan amount annually. FHA loans allow as little as 3.5% down (with a credit score of 580+) but charge their own mortgage insurance premium for the life of the loan. VA and USDA loans offer 0% down for qualifying buyers. PMI is not necessarily a deal-breaker — putting 5–10% down and paying PMI temporarily may be better than waiting years to save 20%, especially in an appreciating market. PMI is cancelable once you reach 20% equity on a conventional loan.
Why do mortgage lenders use 28% of gross income as the housing cost limit?
The 28% guideline, sometimes called the 'front-end ratio,' was established by Fannie Mae and Freddie Mac as a threshold that statistically predicts sustainable homeownership without financial distress. It ensures that housing costs remain manageable even if income dips or unexpected expenses arise. The figure dates to mid-20th-century lending standards but has persisted because it aligns with broad budgeting frameworks — housing taking roughly one-quarter to one-third of gross income leaves room for taxes, retirement savings, and living expenses. Some lenders stretch this to 31% for well-qualified borrowers, but staying closer to 28% provides a meaningful safety buffer.