Mortgage Calculator · Guide
Mortgage Amortization Schedule
The schedule shows how each modeled payment changes the mortgage balance over time.
Opening balance
This is the principal balance before the month's interest and principal are applied.
Interest and principal
Monthly interest equals the opening balance times the monthly rate. Scheduled principal is the fixed principal-and-interest payment minus that interest, capped at the remaining balance. With a 0% rate, principal is divided evenly across the scheduled months.
Extra principal
When an extra-payment plan is active, the schedule reports the actual extra principal applied. On the final payment, planned extra is capped so the ending balance does not go below zero.
Why the mix changes
For a positive fixed rate, early payments generally have more interest because the balance is larger. As principal falls, monthly interest falls and more of the fixed scheduled payment goes toward principal.
Exports
The visible schedule and CSV/TSV/JSON/HTML/DOCX/ZIP outputs all derive from the same result model. Keep a reviewed copy if you need to compare the estimate with lender statements later.