What Is a Mortgage Calculator?
A mortgage calculator is a financial assessment tool designed to estimate your monthly home loan payment based on down payments, interest rates, and loan terms.
Purchasing real estate represents the largest financial investment most consumers will make. Having access to precise calculations is critical for planning. This calculator helps homebuyers visualize the long-term impact of borrowing by generating a detailed principal and interest breakdown alongside a full amortization schedule.
Formula
Monthly payments (P&I) are calculated using the following fixed-rate loan amortization formula:
How to Use This Calculator
- Input Home Price & Down Payment: Enter the purchasing price of the home and the initial cash down payment you plan to make.
- Set Loan Terms: Enter the yearly interest rate offered by your lender, and select your loan term (e.g. 15 or 30 years).
- Taxes & Insurance: Input property taxes, homeowner's insurance, and HOA fees to see a complete monthly cost estimate.
- Review Results: The calculator updates dynamically, showing your monthly payment and total loan interest cost. Click "Show Amortization Schedule" to view the yearly payment grid.
Worked Example
Suppose you buy a home for $400,000 with a $80,000 (20%) down payment, at a 6.5% interest rate on a 30-year term.
1. Compute principal: P = 400,000 − 80,000 = $320,000.
2. Compute monthly rate: r = 0.065 ÷ 12 ≈ 0.005417.
3. Compute number of months: n = 30 × 12 = 360 months.
4. Apply formula: M = 320,000 × [0.005417 × (1.005417)^360] ÷ [(1.005417)^360 − 1] ≈ $2,023/month (P&I).
5. Total interest cost: ($2,023 × 360) − 320,000 = $408,187 paid in interest over 30 years.