Mortgage Repayment Calculator

Mortgage Repayment Calculator

  • Enter the loan amount, interest rate, and loan term.
  • Optionally, you can enter an extra monthly payment to see the effect.
  • Click "Calculate Repayment" to get the loan summary.
  • Click "Clear Results" to reset the results.
  • Click "Copy Results" to copy the results to the clipboard.


The Mortgage Repayment Calculator is a valuable financial tool that helps individuals and organizations alike make informed decisions about their home financing. It allows users to estimate their monthly mortgage payments based on various parameters, providing a clear understanding of their financial commitment over time.

The Concept

At its core, the Mortgage Repayment Calculator operates on a simple yet essential financial concept – amortization. Amortization is the process of paying off a loan, such as a mortgage, in regular installments. Each installment consists of both the principal amount borrowed and the interest accrued on the outstanding balance. As time progresses, the proportion of the payment allocated to the principal and interest changes, with more going towards the principal over the loan term.

The Formulae

To calculate mortgage repayments, the Mortgage Repayment Calculator employs the following key formulae:

Monthly Payment Calculation

The most critical formula for the Mortgage Repayment Calculator is the calculation of the monthly payment, denoted as M:

M = P * (r * (1 + r)^(n) / ((1 + r)^(n) – 1))


  • M is the monthly payment.
  • P is the principal amount borrowed.
  • r is the monthly interest rate (annual rate divided by 12).
  • n is the total number of monthly payments (loan term in years multiplied by 12).

Interest Calculation

The interest portion of each payment can be calculated using the following formula:

Interest Payment = Outstanding Balance * Monthly Interest Rate


  • Outstanding Balance is the remaining principal amount.
  • Monthly Interest Rate is the monthly interest rate.

Principal Payment

The principal portion of each payment can be found by subtracting the interest payment from the total monthly payment:

Principal Payment = Monthly PaymentInterest Payment

Example Calculations

Let’s consider an example to illustrate how the Mortgage Repayment Calculator works:

Suppose you borrow $250,000 for 30 years (360 months) at an annual interest rate of 4.5%.

  1. Calculate the monthly interest rate: r = 4.5% / 12 = 0.375% = 0.00375 (decimal)
  2. Use the monthly payment formula to find the monthly mortgage payment (M): M = $250,000 * (0.00375 * (1 + 0.00375)^360 / ((1 + 0.00375)^360 – 1)) M ≈ $1,266.71
  3. Calculate the first monthly interest payment: Interest Payment = $250,000 * 0.00375 ≈ $937.50
  4. Calculate the first monthly principal payment: Principal Payment = $1,266.71 – $937.50 ≈ $329.21

These calculations repeat every month, with the outstanding balance decreasing and the proportion of the payment allocated to principal gradually increasing.

Real-World Use Cases

The Mortgage Repayment Calculator finds applications in various real-world scenarios:

Home Buying

Prospective homebuyers use the calculator to estimate their monthly mortgage payments, helping them determine whether a particular property fits within their budget. This information is crucial in making informed decisions about purchasing a home.


Homeowners considering refinancing their mortgages can utilize the calculator to evaluate potential savings and the impact of different loan terms and interest rates on their monthly payments.

Financial Planning

Financial advisors and individuals engaged in financial planning use this tool to model different mortgage scenarios as part of a comprehensive financial strategy. It helps in creating a structured plan for long-term financial stability.

Loan Comparison

The calculator allows users to compare multiple loan offers from different lenders. By inputting the loan terms and interest rates, borrowers can assess the most cost-effective option for their needs.


The Mortgage Repayment Calculator is an indispensable tool for anyone involved in the housing market, whether as a buyer, homeowner, or financial professional. It provides a clear and detailed understanding of the financial commitment associated with a mortgage loan, helping users make informed decisions and plan for their financial future.


  1. Pezzini, M. (2017). Mortgage Finance and the Global Financial Crisis: The Emerging Markets’ Experience. Routledge.
  2. Vernimmen, P., Quiry, P., Dallocchio, M., & Le Fur, Y. (2014). Corporate Finance: Theory and Practice. Wiley.
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