Mortgage Amortization & Extra Payment Calculator

See how much of your mortgage payment reduces your balance—and what extra principal payments could change.

This mortgage amortization calculator with extra payments helps homebuyers and homeowners compare a standard fixed-rate repayment schedule with additional monthly principal. Review principal versus interest, estimated interest savings, and the payoff timeline using your own loan assumptions.

One-time digital purchase. The working calculator is delivered as a downloadable HTML file.

See the actual planner

This desktop screen shows the Mortgage Payoff & Amortization Planner included with this product. The loan details are fictional examples.

The regular payment shown separates principal from interest. The toolbar also shows the planner's save, print and backup controls.

Key features and metrics calculated

• Monthly principal-and-interest payment
• First-payment principal versus interest breakdown
• Optional property tax, insurance, PMI and HOA estimates
• Interest saved and time saved with extra monthly principal
• Regular and accelerated payoff dates
• Interactive loan-balance chart
• Monthly and yearly amortization schedules
• Printable PDF view and downloadable CSV schedule

Preview: how extra payments change the numbers

For a fictional $300,000 loan at a fixed 6.5% annual interest rate over 30 years, the monthly principal-and-interest payment is approximately $1,896.20. The first payment includes $1,625 in interest and about $271.20 toward principal.

In a monthly amortization model, paying another $100 toward principal with every payment from month one reduces the payoff time to about 26 years and saves approximately $60,995 in interest. Taxes, insurance, PMI, HOA charges, fees, and penalties are excluded. Your results depend on your loan and how payments are applied.

This is a worked illustration, not a live calculator. See the complete amortization and extra-payment walkthrough.

Compatibility and download format

The working calculator is an HTML file designed to run in a browser. No Excel, Google Sheets or Numbers software is required. Opening downloaded HTML and saving files varies by device; some phone file previews do not run interactive controls. Review our device guide and ask us before buying if you will use only a phone or tablet. The exported CSV schedule opens in compatible spreadsheet software.

Your entries remain in your browser and are not uploaded. Print the results, save a PDF through your browser’s print options, or download a CSV schedule. Printing and file-opening steps vary by device.

How to use the calculator

1. Enter the loan amount, annual interest rate, term, and payment timing requested by the tool.
2. Review the regular principal-and-interest payment and schedule. Keep taxes, insurance, PMI, and HOA estimates separate from the loan calculation.
3. Add an extra monthly principal amount and compare interest saved and the payoff timeline.
4. Print or export the schedule you want to keep.

Before you buy

This calculator models fixed-rate monthly amortization. It does not reproduce every lender’s daily-interest, adjustable-rate, interest-only, or balloon-loan rules. Check your loan documents and confirm with your servicer how extra payments will be applied.

How digital downloads work · Current refund policy. Questions? Email marchelle@roofandratio.com.

Educational planning tool only. Results are estimates and are not a loan quote, appraisal, tax calculation, or financial advice.