How to calculate a mortgage repayment

- Apr 22, 2019

Before you buy a home on a mortgage, you need to know how much you will need to repay your mortgage.

Here’s how we calculate your monthly mortgage payments on a fixed-rate loan:

M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]

Below are the variables to consider when calculating your mortgage:

M = monthly mortgage payment. The number of months to repay your loan.

P = the principal is the initial amount you borrowed.

i = your monthly interest rate. Your lender likely lists interest rates as an annual figure, so you’ll need to divide by 12, for each month of the year. So, if your rate is 14%, then the monthly rate will look like this: 0.14/12 = 0.01166667.

n = the number of payments over the life of the loan. If you take out a 20-year fixed rate mortgage, this means n = 20 years x 12 months per year, or 240 payments.

Mortgage Calculator

Calculate the monthly payment and generate an estimated amortisation schedule.Enter prepayment amounts to calculate their impact on your mortgage. The rates are calculated in Kenya shillings, but you can as well calculate the amount in any other currency

By changing any value in the following form fields, calculated values are immediately provided for displayed output values. Click the view report button to see all of your results.
Monthly Payment:
Report Amortization:
Report Amortization
Please view the report to see detailed results in tabular form.
Please view the report to see detailed results in tabular form.

Mortgage Calculator Definitions

Mortgage Amount

Original or expected balance for your mortgage.

Term in Years

The number of years over which you will repay this loan. The most common mortgage terms are 15 years and 30 years.

Interest Rate

Annual fixed interest rate for this mortgage.

Monthly Payment

Monthly principal and interest payment (PI).

Total Payments

Total of all monthly payments over the full term of the mortgage. This total payment amount assumes that there are no prepayments of principal.

Total Interest

Total of all interest paid over the full term of the mortgage. This total interest amount assumes that there are no prepayments of principal.

Prepayment Type

The frequency of prepayment. The options are none, monthly, yearly and one-time payment.

Prepayment Amount

Amount that will be prepaid on your mortgage. This amount will be applied to the mortgage principal balance, based on the prepayment type.

Start With Payment

This is the payment number that your prepayments will begin with. For a one-time payment, this is the payment number that the single prepayment will be included in. All prepayments of principal are assumed to be received by your lender in time to be included in the following month's interest calculation. If you choose to prepay with a one-time payment for payment number zero, the prepayment is assumed to happen before the first payment of the loan.


Total amount of interest you will save by prepaying your mortgage.

Report Amortization

Choose how the report will display your payment schedule. Annually will summarize payments and balances by year. Monthly will show every payment for the entire term.