Loan Calculator
Payments, total interest, overpayments and a full amortisation schedule. Free, and runs entirely in your browser — nothing you enter is uploaded or stored.
About Loan Calculator
Calculates the monthly payment for an amortising loan, the total interest over its life, and what an extra monthly payment changes. Early payments are mostly interest and late ones mostly principal, which is why overpaying early has a disproportionate effect.
The extra-payment field is the interesting one. On a long mortgage, a modest amount added every month can remove years from the term and a large fraction of the total interest, because every extra pound goes straight against the principal that interest is charged on. A one-off lump sum can be added at any payment too, and the summary compares the result with paying only the instalment: how much sooner the loan ends and how much interest that avoids.
The full amortisation schedule is worked out payment by payment and shown as a table — a row per year, or a row per payment — with a chart of how each year's payments split between principal and interest. Payments can be monthly, fortnightly or weekly, and giving the date of the first one puts real dates on every row and on the payoff. The whole schedule is also available as CSV for a spreadsheet.
Where it helps
- Total interest is shown, which is the number that makes a rate real.
- Models extra payments and a one-off lump sum, and reports the time and interest they save.
- A full amortisation table by year or by payment, with dates, a principal-versus-interest chart and a CSV copy.
- Works for any amortising loan — mortgage, car finance, personal loan.
- Runs locally, so nothing about your finances is transmitted.
Limits
- It assumes a fixed rate for the whole term; variable and tracker rates will diverge.
- Fees, insurance, taxes and arrangement costs are not included, so a real APR will be higher.
- Some lenders charge early repayment penalties that cancel part of the overpayment benefit.
- It is a calculator, not financial advice — confirm the numbers with your lender before deciding.
Frequently asked questions
Why is so much of my early payment interest?
Interest is charged on the outstanding balance, which is at its largest at the start. As the principal falls, the interest share falls with it.
How much does overpaying really save?
More than people expect. Try a small extra amount and compare the total interest — on a long term the difference is usually years and a substantial sum.
Does this match my lender's figure exactly?
It will be close. Lenders differ in day-count conventions, rounding and fees, so treat this as a planning estimate.
Is the rate monthly or annual?
Annual. It is divided into a monthly rate internally, which is the standard amortisation convention.
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