Overpay vs remortgage calculator
Last checked UK · illustrative onlyNot a lender or brokerAboutDisclaimer
RLPublished by Rodway Labs — not a mortgage adviser
Compare applying spare cash to the current mortgage with remortgaging that balance. Illustrative only — it does not say which option you should choose.
Methodology & assumptions · Last checked
Assumptions
- Starter is £200,000 at 4.49% over 20 years, with £10,000 cash — not the £185,000 EXAMPLE house.
- Rates are held constant. No overpayment allowance is deducted before an ERC.
- Does not model offset accounts or a lender declining the new rate.
Your inputs
Starter figures are UK EXAMPLE values you can edit. Scenario rates, not a market quote. 4.19%, 4.39%, 4.14% and 7.49% SVR on this site are labelled EXAMPLE figures, last checked 30 September 2026. Results update as you type.
Results
Overpay balance after cash
£190,000
Overpay monthly
£1,201.01
Overpay interest in window
£16,542
Remortgage monthly
£1,232.08
Remortgage interest in window
£16,232
ERC
Estimate from the terms you entered, not your contract
£4,000
Net switching cost
ERC + fees − cashback
£5,499
Overpay all-in (interest)
£16,542
Remortgage all-in
Interest plus net switching cost. Not a recommendation.
£21,731
Overpay reduces the balance by the cash entered, capped at the balance. Remortgage keeps the balance and adds ERC plus fees net of cashback. Estimated break-even is not shown: compare the two all-in figures. Actual results change if rates, fees or terms change.
Illustrative only — not personalised advice, not a credit or mortgage offer, and not an FCA-regulated recommendation. Check your lender offer for ERC, fees and product terms (and the Key Facts Illustration). Rates, fees and tax rules change. England & Northern Ireland focus where tax/SDLT rules apply; Scotland and Wales differ. Full calculator disclaimer.
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.
Interest uses the same amortising schedule as the other tools. Net switch cost is ERC plus fees minus cashback, floored at zero.
- Starter is £200,000 at 4.49% over 20 years, with £10,000 cash — not the £185,000 EXAMPLE house.
- Rates are held constant. No overpayment allowance is deducted before an ERC.
- Does not model offset accounts or a lender declining the new rate.
How this calculator works
Use this when you have a lump sum and want to see overpaying the current deal beside remortgaging. It does not choose for you. You need the balance, both rates, the term, the cash, the fees and the ERC that applies.
Worked example
Scenario rates, not a market quote
Starter case, not the £185,000 house: £200,000 balance, 20 years, current 4.49%, £10,000 cash, remortgage rate 4.19%, 2% ERC, £1,499 fees, no cashback, 24-month window. Scenario rates, last checked 30 September 2026.
Cash reduces only the overpay balance. The remortgage path still carries the ERC and fees you enter. A lower all-in figure is cheaper on these inputs only.
What this ignores
- A 10% overpayment allowance. Lower the ERC if your offer would not charge on this cash.
- Offset accounts and a lender declining the new rate.
- Tax and a future SVR.
Questions
- What does this calculator do?
- It compares interest after a lump-sum overpayment with interest plus ERC and fees if you remortgage.
- Who is it for?
- Someone with spare cash who is also looking at a remortgage quote.
- What do I need?
- Balance, current rate, term, cash, the remortgage rate, fees and the ERC clause.
- What does the result mean?
- Two all-in figures over the window you set. It is not a recommendation.
- What is not included?
- Credit decisions and valuation gaps. A lender figure can differ.