How is the monthly payment calculated?
The payment excluding insurance follows the constant annuity formula: m = P × r ÷ (1 − (1 + r)⁻ⁿ), where P is the principal, r the monthly rate (annual rate divided by 12) and n the number of payments. Each installment first covers the month’s interest, computed on the outstanding capital, and the remainder amortizes the principal. This is why the interest share is highest at the start of the loan and shrinks with every payment.
