Loan & Mortgage Calculator: how it works
A short guide to repayment and amortisation maths — the formula, how to read the schedule, and how to use the calculator.
Open the Loan Calculator →What this tool does
The Loan & Mortgage Calculator turns a loan amount, interest rate, and term into a monthly repayment, the total interest you'll pay, a chart of the falling balance, and a year-by-year amortisation schedule. It all runs in your browser.
How to use it
- Open the Loan Calculator.
- Enter the loan amount, annual interest rate, and term in years.
- Read the monthly payment, total interest, and total cost — they update as you type.
- Scan the chart and the per-year schedule to see how the balance falls.
The formula
Repayments use the standard amortisation formula:
M = P · r / (1 − (1 + r)−n), where P is the amount,
r is the monthly rate (annual rate ÷ 12 ÷ 100), and n is the
number of monthly payments (years × 12).
Reading the schedule
Each payment is split between interest and principal. Early on, most goes to interest; as the balance shrinks, more goes to principal. That's why paying a little extra early saves a disproportionate amount of interest over the life of the loan.
Your numbers stay private
All calculations happen locally in your browser — nothing you enter is uploaded.
FAQ
How is the repayment calculated?
With the amortisation formula above, for a fixed-rate loan paid monthly.
What is amortisation?
Paying off a loan in equal instalments that shift from mostly interest to mostly principal.
Is my data uploaded?
No — it all runs in your browser.
This tool gives estimates for general use and is not financial advice.
Ready to try it? Open the Loan Calculator →