Overpaying vs remortgaging — compare spare cash and switch cost

Spare cash can go into the mortgage you already have, or it can help fund a switch to a new product. Those are not the same decision. Overpaying reduces the balance on the current rate and usually shortens the term. Remortgaging changes the rate (and often the lender), but can trigger an early repayment charge (ERC), product fees, legal costs and cashback clawback rules. This guide compares those paths on paper. It does not say you should overpay, and it does not say you should remortgage.

Figures use our shared site EXAMPLE house. They are illustrative only. Your balance, rate, fees, ERC schedule and free overpayment allowance will differ. Run your own numbers in the Mortgage overpayment calculator and the Remortgage true cost calculator. Neither tool is advice.

Two different questions

Overpaying asks: if I keep this deal, how much interest do I avoid by paying more than the contractual repayment — and do I stay inside the annual overpayment allowance so I do not trigger an ERC on the excess?

Remortgaging asks: after ERC (if any), fees and cashback, is the new path cheaper over a clear horizon than staying put — and is the alternative a calm stay on the current fix, a product transfer, or a stretch on a reversion rate?

Mixing the questions muddies the maths. A lower headline rate does not automatically beat a series of overpayments. A large overpayment that breaches the allowance can itself create an ERC. Treat allowance wording and the full switch cost as first-class inputs, not afterthoughts.

Independent consumer material from MoneyHelper on paying off a mortgage early stresses checking early repayment charges and keeping other priorities covered before you put extra into the loan. The Financial Conduct Authority (FCA) publishes consumer pages on mortgages and arranging a new deal so it can start when the existing one ends. Those sources explain process and protections. They are not a substitute for your own offer and Key Facts Illustration.

Warn first: overpayment allowances and ERCs

Many UK fixed-rate (and some other) deals allow a free annual overpayment band — often described as a percentage of the balance or of the original advance. A common labelled illustration is about 10% a year, but the real figure, reset date and whether regular extras and lump sums share one pot are product-specific. Exceeding the allowance during the ERC period can trigger a charge on the excess, calculated under the offer wording.

Full redemption when switching lender is a different event: the ERC may apply to the whole balance redeemed (subject to any free band and step-down schedule), plus exit or admin fees. Partial overpayments and a full remortgage can both create charges. Check the offer before you treat either path as “free”.

On the shared EXAMPLE balance of £185,000, a labelled 10% annual allowance would be £18,500 in year one. Monthly extras of £100 (£1,200 a year) or £200 (£2,400 a year) sit well inside that EXAMPLE band. A single lump sum of £25,000 would exceed it by £6,500 — and if an EXAMPLE 2% charge applied to that excess only, that would be £130 before you count any other fees. Always replace those labels with your lender’s figures.

The EXAMPLE house (shared site case)

Hold these labelled EXAMPLE inputs constant through the worked paths below. Rates that are not live market prices are marked EXAMPLE.

• Outstanding balance: £185,000
• Remaining term: 22 years
• Current fixed rate: EXAMPLE 4.19%
• Months left on the deal: 4
• EXAMPLE ERC if you leave now at 2% of balance: £3,700
• New-lender rate if you remortgage: EXAMPLE 4.14%
• Fees to switch: £1,499 (EXAMPLE product fee £999 + legal £500)
• Cashback on the remortgage path: £250 (net fees £1,249)
• Comparison horizon for switch maths: 24 months
• Labelled free overpayment allowance for the worked overpay paths: 10% of balance (£18,500) — illustration only

On a capital-and-interest repayment basis, holding balance and term constant for a simple comparison:

• Monthly contractual repayment at EXAMPLE 4.19%: about £1,074
• Monthly contractual repayment at EXAMPLE 4.14%: about £1,069
• Monthly difference if you switch: about £5

That tiny payment gap cannot repay a £3,700 ERC on its own. The interesting comparison is therefore not “which rate looks nicer”, but whether spare cash cuts more interest as an overpayment on 4.19% than as a funded early switch to 4.14%.

Path A — stay on the current deal and overpay (within allowance)

Keep EXAMPLE 4.19%. Add a regular overpayment and assume the contractual payment stays the same so the extra shortens the term — the same assumption our overpayment calculator uses. Year-one extras stay inside the labelled 10% EXAMPLE allowance.

• Extra £100 a month: about £99 less interest over 24 months versus paying the contract only; over the full remaining term, about £14,350 less interest and about 34 months off the schedule; year-one extras £1,200 (inside £18,500 EXAMPLE allowance)
• Extra £200 a month: about £198 less interest over 24 months; over the full term, about £24,940 less interest and about 61 months off; year-one extras £2,400 (still inside the EXAMPLE band)

Those lifetime figures compound because every extra pound reduces the balance that future interest is charged on. They are not free money: the cash has left your account. The comparison is whether that same cash, used instead to pay an ERC and fees for a slightly lower rate, does better or worse on paper.

Path B — remortgage now (pay ERC and net fees)

Leave today at EXAMPLE 4.14%. Pay the EXAMPLE ERC of £3,700 and net fees of £1,249 (upfront hit £4,949). Make no overpayments on the new deal for this column.

• Interest over 24 months at EXAMPLE 4.19% (stay, no overpay): about £15,080
• Interest over 24 months at EXAMPLE 4.14% (leave): about £14,897
• Interest saving from the rate cut alone: about £183
• Upfront hit to leave: £4,949
• Net true cost of leaving versus staying with no overpay: about £4,766 against early exit over this 24-month window

On these EXAMPLE figures, early remortgage loses on paper against simply staying on 4.19% with no extras. The rate gap is too small relative to the charge. Folding your own ERC, fees and rates into the true cost calculator is the way to test a wider gap or a different horizon.

Same spare cash — overpay versus fund the switch

Now put Path A and Path B side by side with the same 24-month window and the same EXAMPLE house.

• Stay + £200 a month overpay: interest over 24 months about £14,882 — roughly £198 less than stay-with-no-overpay — and you have put £4,800 of capital into the loan, with no EXAMPLE ERC if you remain inside the labelled allowance
• Leave now to EXAMPLE 4.14% with no overpay: interest about £14,897 (similar 24-month interest to the £200 overpay path) but you have also paid £4,949 in ERC and net fees

On this labelled EXAMPLE, the overpay path cuts a similar amount of 24-month interest to the early switch — without the £4,949 exit stack — while the remortgage path spends almost the same cash order-of-magnitude on charges that never reduce the balance. That is why fees and ERCs decide before a five-basis-point headline gap.

If the ERC were zero (for example because completion lands on or after the deal end date), the switch maths changes: net fees of £1,249 would need to be weighed against the smaller rate gap and against what the same cash would do as an overpayment. Waiting four months on this EXAMPLE house avoids the £3,700 charge entirely for only a short delay on the current fix.

When the switch column can still look stronger

Early remortgage can still win on paper when the realistic alternative is not “stay on a calm fix and overpay”, but “face a much higher reversion rate for a long stretch” or “sit on a locked rate far above anything available now”. Those cases are covered in more depth in our remortgaging early guide. Even then, spare cash used to overpay after a cheaper deal starts is a separate, later decision — and the new product’s own overpayment allowance still needs a check.

Liquidity matters too. Overpayments reduce a mortgage balance; they are not a rainy-day fund. MoneyHelper’s early-repayment material emphasises weighing other debts, emergency reserves and charges before you commit extra to the loan. This site does not rank those priorities for you.

A simple checklist before you choose a column

• Free overpayment allowance: percentage or amount, reset date, and what already counts this year
• ERC method, step-down dates, and whether full redemption differs from partial extras
• Exact deal end date and whether a remortgage can complete on or after that date
• Product, valuation, legal and broker fees; cashback and clawback
• Whether switch fees are paid upfront or added to the new loan
• One comparison horizon applied to every path (for example 24 months)
• Whether the cash you would overpay is money you can afford to lock into the property

Estimate extras and allowance headroom in the overpayment calculator. Fold ERC, fees and rate differences into the true cost view. If the net figure still favours waiting or staying, the paper answer is not “chase the lower advert”.

Sources and further reading

We write in our own words. For independent consumer guidance, see MoneyHelper on paying off a mortgage early and the FCA’s consumer mortgages pages. Those sources explain process, costs to check, and consumer protections. They are not a substitute for reading your own lender offer.

Disclaimer

This guide and the worked EXAMPLE paths are illustrative only. They are not personalised financial advice. They are not a credit or mortgage offer. They are not an FCA-regulated recommendation. Check your lender offer (and Key Facts Illustration) for ERC, overpayment allowance, fees and product terms. Rates and charges change. If you want advice on your situation, speak to an FCA-authorised mortgage adviser.

Next steps

Run your extras through the Mortgage overpayment calculator with your real annual allowance. Compare any switch in the Remortgage true cost calculator. Read retention quotes alongside new-lender figures. This site helps you organise the numbers; it does not tell you to overpay or to remortgage.