Mortgage Amortization Calculator
See which mortgage payments go to interest and which reduce your balance. This tool compares your entered extra principal against the same mortgage without extras, supplies dated rows and exports a CSV. Use the Mortgage Calculator when starting with property price and down payment.
Your result
How the calculation works
The base monthly payment amortizes outstanding principal over the entered term. Monthly interest = opening balance × annual rate/12. Extra principal follows the normal payment. Interest saved = baseline interest − interest with extras; payments saved = baseline periods − new periods. Property tax and insurance are displayed separately.
Worked example
A $12,000 mortgage balance over one year at zero interest requires $1,000 monthly principal. Adding $200 monthly clears the balance in ten payments, saving two payment periods. Extra payments do not save interest when the interest rate is zero.
Assumptions and limitations
This is a fixed-rate, monthly principal-and-interest mortgage. Start date is the balance date; the first payment falls one month later. Optional annual property tax and insurance remain constant and are not loan interest or principal. Fees, daily accrual, mortgage insurance and changing rates are not added automatically.
The extra-payment comparison is specific to your assumptions and is not advice to prepay or refinance. Check loan restrictions and lender calculations. The dated table and CSV make this page distinct from the purchase-budget mortgage tool; they are not separate URLs for numeric permutations.
Sources and editorial responsibility
Maintained by Renvoro Pty Ltd. These mathematical estimates do not provide financial, tax, legal or investment advice.
Method reviewed 2026-10-08. Calculation standards · Report an issue