Mortgage Calculators
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When rates move, should you pay to break your fix early? These tools give you a clear, numbers-based answer before you speak to a broker.
Is it worth breaking a fixed-rate mortgage early?
Leaving a UK fixed-rate mortgage before the deal ends normally triggers an Early Repayment Charge — commonly 1% to 5% of the outstanding balance, often stepping down for each remaining year. Switching is worth it only if the interest you save on a cheaper rate overtakes that charge, plus any product, valuation and legal fees, before your current deal would have ended anyway.
Three numbers decide it: how much lower the new rate is, how long is left on your fix, and the total cost of switching. Put them together and you get a break-even month — the point at which cumulative interest saved passes the cost of getting out. Break even comfortably inside your remaining fixed term and the switch has paid for itself with time to spare. Break even after it, and you have paid for a rate you could have moved to for free.
The costs people forget
The Early Repayment Charge is the headline number, but rarely the only one:
- Product or arrangement fee on the new deal, which can run to four figures. Lenders often let you add it to the loan — convenient, but you then pay interest on it for the full term.
- Valuation and legal fees, sometimes covered by the new lender as an incentive, sometimes not.
- A higher loan-to-value band if you add fees to the balance, which can push you into a worse rate than the one advertised.
One detail worth checking before you do anything: the exact date your Early Repayment Charge steps down. On many deals it drops by a percentage point each year, so a switch that looks marginal today can look obvious a few weeks later. Your lender will give you a redemption figure on request — use that, not an estimate, once you are close to deciding.
Overpaying can beat switching
Most UK fixed deals let you overpay a set amount each year without triggering the charge — commonly 10% of the outstanding balance, though the allowance and the way it is measured vary by lender. Overpaying inside that allowance shortens your term and cuts total interest with no switching cost at all, which is frequently the better move when the gap between your rate and the market is small.
The comparison to run is straightforward: the interest saved by overpaying within your allowance for the rest of the fix, against the interest saved by switching minus the full cost of getting out. The Ditch Your Fix Calculator handles the switching side of that.
Why your mortgage sits outside the debt snowball
A mortgage is secured debt, so it never goes into a snowball or avalanche plan. It is a priority bill paid in full first, because missing payments risks your home rather than just interest and charges.
The debt snowball and debt avalanche are built for unsecured, non-priority debt: credit cards, store cards, overdrafts, personal loans, car finance and buy-now-pay-later. Those you can reorder freely, because the only cost of taking longer is interest. A mortgage cannot be reordered that way, and neither can other priority bills like council tax, energy or money owed to HMRC. If you are carrying both, the usual sequence is priority bills in full, then unsecured debt through a payoff plan, then mortgage overpayments with whatever is left. Our debt payoff guides cover the unsecured side in detail.
Frequently asked questions
Where do I find my exact Early Repayment Charge?
It is set out in your original mortgage offer and repeated on your annual mortgage statement, usually as a percentage of the outstanding balance with a separate rate for each remaining year of the deal. Your lender will also give you a redemption figure on request, which is the definitive number. Check the date the charge steps down — waiting a few weeks can cut it by a full percentage point.
Can I overpay my mortgage without triggering the Early Repayment Charge?
Most UK fixed-rate deals allow you to overpay a set amount each year penalty-free, commonly 10% of the outstanding balance, though the exact allowance and how it is calculated vary by lender. Overpaying within that allowance shortens your term without any switching cost, which is often the better move when the gap between your rate and the new one is small.
Why is my mortgage not part of the debt snowball?
The debt snowball is built for unsecured, non-priority debt such as credit cards, overdrafts, personal loans and car finance. A mortgage is secured on your home, so missing payments risks possession rather than just interest and charges. That makes it a priority bill you pay in full first, outside any payoff plan.
Does remortgaging early affect my credit file?
A new mortgage application involves a hard credit search and a fresh affordability assessment, both of which are recorded. A single application is not usually significant, but several in a short period can be. Your eligibility for the new rate also depends on your current income, loan-to-value and credit history, so the cheapest advertised rate is not automatically available to you.
In depth · Updated · 4 min read
Fixed rate ending? Your four options, compared
When a fixed-rate mortgage deal ends, you don't have to accept whatever your lender offers. There are four routes, and the right one depends on your rate, your credit file and whether you can repay part of the balance.
1. Product transfer with your current lender
A new deal with the same lender, usually available from a few months before your fix ends. There is normally no new valuation or full affordability assessment if you are not borrowing more, which makes it the easiest route — and often the only realistic one if your credit file has taken a hit since you took the mortgage out.
2. Remortgage to a new lender
A fresh application elsewhere, with a full credit check and affordability assessment. It opens up the whole market and can beat your lender's retention rate, but it involves legal work, a valuation and sometimes fees. A whole-of-market broker can compare both routes for you.
3. Drift onto the standard variable rate
Do nothing and most mortgages move to the lender's standard variable rate (SVR), which is usually well above fixed-rate deals. It rarely makes sense for long, but there are no early repayment charges on an SVR, which can be useful for a few months while you sort out a move or a lump-sum repayment.
4. Overpay before or at the switch
Most fixed deals let you overpay up to around 10% of the balance each year without an early repayment charge. Overpaying before the switch reduces the balance your next rate applies to and can move you into a lower loan-to-value band.
Thinking of leaving before your fix ends? Then the early repayment charge is the deciding number — the ditch your fix calculator shows whether a cheaper rate today saves enough interest to cover it.
Methodology & trust
Written and reviewed by Peter Barclay, a UK Chartered Mechanical Engineer — who builds and maintains these tools, pairing engineering-mathematics training with a focus on the mechanics of debt repayment. The calculators use standard amortization formulas and fixed repayment orders. Read our methodology or more about the author.
DebtSnowball is not a financial adviser and is not authorised or regulated by the FCA (Financial Conduct Authority). These tools are for education and information only, not financial advice. If you are struggling with debt, get free, impartial help from StepChange, National Debtline or Citizens Advice.
Last reviewed: October 2026 Spotted an error? Report it and we will fix it.