The Practical Mortgage Guide

Every mortgage payment is the same size, but its composition changes. Early payments are mostly interest; later payments are mostly principal.

The instalment formula is EMI = P × r × (1+r)^n ÷ ((1+r)^n − 1), where r is the monthly rate and n the number of payments.

Small prepayments early in the term remove interest that would have compounded for decades, which is why they cut the total cost so sharply.