THE NUMORIX GUIDE
How to use the Mortgage calculator
Last reviewed September 12, 2026
What this mortgage calculator does
This calculator estimates a fixed-rate monthly housing payment from the home price, down payment, term, interest rate, property tax, insurance, and HOA dues. It separates principal and interest from recurring housing costs and shows how the loan balance changes over time.
Mortgage payment formula
First, the loan amount is L = home price - down payment. The principal-and-interest payment is M = L[r(1+r)^n] / [(1+r)^n - 1], where L is the loan amount, r is the monthly rate (annual rate / 12), and n is the total number of monthly payments (years x 12). The estimated housing payment then adds annual property tax / 12, annual insurance / 12, and monthly HOA dues.
Worked example
Suppose a home costs $400,000 with an $80,000 down payment, a 30-year term, and a 6.5% annual rate. The loan amount is $320,000 and the monthly principal-and-interest payment is about $2,023. Adding $400 for property tax, $117 for insurance, and $75 for HOA dues gives an estimated monthly housing cost of about $2,615.
How to interpret the result
The payment is a scenario estimate built from your inputs. A longer term usually lowers the monthly payment but increases total interest. Taxes, insurance, HOA dues, mortgage insurance, closing costs, points, and lender-specific fees can change the amount you actually pay.
Common mistakes to avoid
Use the loan amount after the down payment rather than the home price. Convert an annual rate to a monthly rate before using the formula. Do not treat property tax and insurance estimates as fixed if the property, location, coverage, or assessment can change.
Assumptions and limitations
The model assumes a regular fixed-rate repayment schedule and does not underwrite credit, income, lender eligibility, or local tax rules. PMI and other mortgage insurance are not inferred unless the calculator provides an input for them. Compare the result with a lender disclosure before making a decision.