How mortgage amortisation works
Each fixed payment first covers interest on the outstanding balance. The remainder reduces principal, so the interest share normally falls over time.
Why the balance falls slowly at first
Interest is calculated on the remaining principal. Early in a long loan, that balance is high, so more of the fixed payment goes to interest. Download the calculator’s CSV schedule to inspect every period.
Overpayments
Extra principal can reduce both future interest and the payoff date, but verify prepayment limits and penalties with the lender.