THE NUMORIX GUIDE
How to use the Mortgage Affordability Calculator
Last reviewed September 14, 2026
What this calculator does
The engine first subtracts monthly property tax, insurance, and HOA from the monthly housing budget.
Formula and method
The engine first subtracts monthly property tax, insurance, and HOA from the monthly housing budget. It solves the remaining principal with the fixed-payment mortgage formula, loan = payment x ((1 + r)^n - 1) / (r x (1 + r)^n), where r is the monthly rate and n is loanTerm x 12, then adds the down payment to get max home price.
Variables and inputs
Enter monthly housing budget, down payment, annual interest rate, loan term in years, and monthly property tax, insurance, and HOA. The UI defaults to $2,500 budget, $60,000 down, 6.5%, 30 years, $300 tax, $100 insurance, and no HOA.
Worked example
With the defaults, housing payment available for principal and interest is $2,500 - $300 - $100 = $2,100. At 6.5% for 30 years, the solved loan is about $332,243, maximum home price is about $392,243 after adding the $60,000 down payment, and the engine reports about $423,757 total interest.
How to interpret the result
The maximum is the home price supported by the entered monthly ceiling and mortgage assumptions. It is a mathematical ceiling, not an underwriting decision or a recommendation to spend the full amount; maintenance, reserves, closing costs, and changing ownership costs still matter.
Common mistakes to avoid
Enter the full housing budget rather than only principal and interest. Keep property tax, insurance, and HOA as monthly amounts because the engine subtracts them directly. Do not treat down payment as part of monthly affordability or assume it covers closing costs.
Assumptions and limitations
The route omits credit, income, debt-to-income, PMI, closing costs, maintenance, utilities, rate changes, lender limits, taxes beyond the entered monthly amount, and insurance changes. A zero-rate branch is supported, but the pure engine does not validate negative inputs or an unrealistic term.