Mortgage Calculator | Calculate monthly payment & overpayment

What is a mortgage?
A mortgage is a loan used to purchase real estate, where the property itself serves as collateral. You repay the loan in monthly installments over the loan term. Each payment covers both interest and a portion of the principal.
Annuity vs differentiated payments
Annuity: equal payments throughout the term — easy to budget, but total interest is higher. The interest share is large at first and shrinks over time. Differentiated: fixed principal part each month, so payments decrease as the balance falls. Lower total overpayment, but early payments are noticeably larger.
How is the payment calculated?
For annuity, the payment is fixed and calculated so that the loan is fully repaid by the end of the term.
Annuity: Payment = Principal × r / (1 − (1 + r)^−n) where r = annual rate / 12, n = term in months
For differentiated payments, the principal part is constant (loan ÷ months) and the interest decreases each month as the balance shrinks.
Differentiated: Payment_i = Principal/n + (Principal − Principal/n × (i−1)) × r where r = annual rate / 12, n = term in months
What is the overpayment?
Overpayment is the total interest paid over the life of the loan — the difference between the total amount paid and the original loan amount. Differentiated payments result in lower total overpayment compared to annuity, especially for longer terms.