Mortgage overpayment calculator
Paying a little extra each month has an outsized effect, because every pound of overpayment comes straight off the balance rather than being split with interest. Enter what you owe now to see the difference.
Your mortgage now
What you would overpay
What it saves you
Interest saved
£0.00
Enter an overpayment to see the difference.
The two paths compared
The gap between the lines is what overpaying buys you.
Why overpaying works so well
On a normal repayment mortgage, each monthly payment is split between interest and capital. Early in the term, most of it is interest, because interest is charged on a large outstanding balance. An overpayment is different: it goes entirely against the capital.
That smaller balance is then charged less interest the following month, and every month after that. The saving compounds, which is why £150 a month can save tens of thousands over a full term.
A worked example
On £200,000 at 4.5% with 22 years left, the normal payment is around £1,258 a month. Adding £150 takes it to £1,408, clears the mortgage roughly three years early, and saves close to £25,000 in interest. The total you actually overpay is far less than the interest you avoid, which is the whole point.
Check this before you overpay
- Your lender's annual limit. Most fixed-rate deals allow overpayments of up to 10% of the balance each year. Go above that and you may face an early repayment charge, often a percentage of the amount overpaid.
- Whether the term or the payment reduces. Some lenders keep your term the same and lower the monthly payment instead, which saves far less interest. This calculator assumes the term shortens. Ask your lender which they do, and specify what you want.
- Higher-interest debt first. Clearing a credit card at 22% saves more than overpaying a mortgage at 4.5%. Mortgages are usually the cheapest debt you have.
- Your emergency savings. Money paid into a mortgage is difficult to get back. Most guidance suggests keeping three to six months of essential spending accessible before overpaying.
- Savings rates. If you can earn more in savings after tax than your mortgage rate, saving may beat overpaying. This changes as rates move.
What this assumes
The rate stays the same for the whole remaining term, overpayments start immediately and continue every month, interest is charged monthly, and there are no fees or early repayment charges. Real mortgages usually revert to a different rate after the fixed period ends, so treat this as an illustration of the effect rather than a forecast.