Advanced Mortgage Affordability Calculator
Find the maximum home price you can afford based on income, existing debts, down payment, taxes, and interest rate. Essential for buyers who want a realistic budget before starting their home search.
About this calculator
Lenders typically use two affordability benchmarks: the front-end ratio (housing costs ≤ 28% of gross monthly income) and the back-end ratio (all debts ≤ 36–43%). This calculator uses the stricter 28% front-end rule to determine the maximum allowable monthly housing payment: Max Housing Payment = Gross Monthly Income × 0.28 − Monthly Debts − Estimated Property Tax − $200 (insurance estimate). The remaining budget is then used to back-solve the standard mortgage amortization formula for the maximum loan amount: Loan = Payment × (1 − (1 + r)^−n) / r, where r is the monthly rate and n is the number of payments. Adding your down payment gives the maximum affordable home price.
How to use
Say your gross monthly income is $7,000, monthly debts (car, student loan) total $500, down payment is $40,000, interest rate is 6.5%, loan term 30 years, and property tax rate is 1.2%. Step 1 — Max housing payment: $7,000 × 0.28 = $1,960, minus $500 debts, minus ~$80 estimated taxes, minus $200 insurance = ~$1,180 for principal and interest. Step 2 — Solve for loan: $1,180 × (1 − (1.00542)^−360) / 0.00542 ≈ $186,500. Step 3 — Add down payment: $186,500 + $40,000 = ~$226,500 maximum home price.
Frequently asked questions
What debt-to-income ratio do mortgage lenders use to determine affordability?
Most conventional lenders look at two ratios. The front-end ratio compares your housing costs to gross income and should stay at or below 28%. The back-end ratio includes all monthly debt payments and should generally not exceed 36–43%, depending on the loan type. FHA loans may allow back-end ratios as high as 50% with compensating factors such as strong credit or large reserves.
How does a larger down payment affect how much house I can afford?
A larger down payment directly increases your maximum home price dollar for dollar, since the loan amount stays the same while your equity stake grows. It also reduces your monthly mortgage payment, lowers or eliminates private mortgage insurance (PMI), and can help you qualify for a lower interest rate. Even an extra 5% down can meaningfully expand your purchasing power or reduce long-term costs.
Why does the affordability calculator include property taxes and insurance in the housing payment?
Lenders evaluate total housing cost, not just principal and interest, when assessing affordability. Property taxes and homeowners insurance are typically collected monthly into an escrow account alongside your mortgage payment. Excluding them from the calculation would overestimate how much loan payment you can sustain, leading to an inflated home price estimate that could stretch your budget dangerously thin.