Mortgage overpayment calculator
Last checked UK · illustrative onlyNot a lender or brokerAboutDisclaimer
RLPublished by Rodway Labs — not a mortgage adviser
See how monthly or one-off overpayments reduce interest and term. Enter your annual overpayment allowance to flag possible ERC risk.
Methodology & assumptions · Last checked
Your inputs
Starter figures are UK examples you can edit — replace them with your balance, rate, term and fees. Results update as you type.
Results
Baseline term
20 years
New term
16 years
Months saved
48
Interest saved
£22,936
Year-1 overpayments
£2,400
Allowance amount
£20,000
Illustrative only — not personalised financial advice and not an FCA-regulated mortgage recommendation. Check your offer, Key Facts Illustration, and lender terms. Rates, fees and tax rules change. Focus is England & Northern Ireland where tax/SDLT rules apply; Scotland and Wales have different property tax regimes. Full calculator disclaimer.
What to do next
Methodology, equations & assumptions
Last checked . Figures are illustrative; tax and product rules can change. England & NI focus for SDLT-related tools — Scotland (LBTT) and Wales (LTT) differ.
Month-by-month amortisation with extra capital reduction each month (and optional one-off in month 1), compared with a baseline schedule at the same rate and term.
- Overpayments reduce term (not payment) by default.
- Annual allowance is user-entered — check your offer.
- Does not model stepped ERCs or cashback clawback.
Notes & FAQs
- Do overpayments reduce the term or the payment?
- This tool assumes overpayments reduce the term while the contractual payment stays the same — a common default. Some lenders let you reduce the payment instead.