UK mortgage overpayment optimiser
Pay less interest.
Own your home sooner.
See the impact of regular and lump-sum overpayments — and whether your plan could exceed your penalty-free annual allowance.
✓ No signup✓ Nothing stored✓ Runs in your browser
Example overpayment result
£38,742
illustrative interest saved
6y 4msooner
£250extra / month
10%allowance modelled
Your result is calculated from your own balance, rate, term and allowance.
Mortgage overpayment calculator
Build a plan that fits your mortgage
We calculate month-by-month, compare against your normal mortgage, then test your proposed overpayments against your annual allowance.
Your projected outcome
Calculating…
Your plan fits the modelled allowance.
We’ll show how much headroom you have in your first allowance year.
Normal mortgage— / month
Your overpayment plan— / month
What if you changed the monthly overpayment?Instant comparison
How we calculated this
We simulate the mortgage month-by-month using the interest rate and remaining term you enter. Overpayments reduce principal immediately. The allowance check uses the allowance model you select, so it is only as accurate as the rule you enter.
Built around the question calculators miss
“Can I actually overpay this much without a charge?”
Most calculators stop at interest saved. This one also helps you model the overpayment restriction you actually have to live with.
Allowance-aware
Model a percentage of the opening balance, a percentage of the original balance, or a fixed annual amount.
Month-by-month maths
No rough multiplier. We amortise the balance and apply overpayments as the mortgage changes.
Decision-first results
See interest saved, time saved and allowance headroom together instead of hunting through a spreadsheet.
Private by default
The MVP performs calculations in your browser. The figures you enter are not sent anywhere by this static version.
Before you overpay
Three checks worth making
Annual allowances, reset dates and early repayment charges vary by lender and product. Use the rule in your own documents.
Money paid into a standard mortgage usually cannot simply be withdrawn again. Consider your emergency savings before committing cash.
A competitive savings account, ISA, pension or other use of cash may be better for some people. This calculator is information, not personalised advice.
FAQ
Mortgage overpayment questions
What does a 10% overpayment allowance mean?
It depends on the mortgage. Some lenders calculate the allowance from a balance on a specific date, others use different rules. Enter the rule that matches your mortgage documents rather than assuming every lender works the same way.
Does an overpayment reduce my payment or my term?
Lender treatment varies. If your required payment remains unchanged, reducing the balance generally shortens the term. Some lenders recalculate the monthly payment instead. Confirm how yours handles overpayments.
Is overpaying always better than saving?
No. Interest rates, tax, access to cash, emergency savings and your wider financial situation matter. A mortgage overpayment gives a return through interest avoided, but it reduces liquidity.
Does this include early repayment charges?
No. The tool flags when your planned overpayments exceed the allowance you entered, but it does not calculate a lender-specific early repayment charge. Check the charge schedule in your mortgage offer.