The Mortgage Overpayment Calculator shows you exactly how much time and interest you can save by paying more than your required monthly mortgage payment. Enter your current balance, interest rate and remaining term, then choose either a regular monthly extra amount or a one-off lump sum, to see your new payoff date, the time you'll save, and the total interest saved compared with sticking to your original repayment schedule.
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You are looking at how making extra payments on your current mortgage balance changes your repayment schedule. The calculator runs a month-by-month amortisation of your loan both with and without the overpayment you've entered, so you can see the real impact on your payoff time and total interest.
Based on your mortgage balance, interest rate and remaining term, the calculator first works out your standard monthly payment using the standard repayment formula. It then simulates your mortgage month by month — once without any overpayment, and once with your chosen monthly extra amount or lump sum applied — to work out the new payoff time, time saved and total interest saved.
Your calculation summary will appear here once figures are entered above.
This calculator provides a general estimate based on a standard repayment mortgage and a constant interest rate for the full remaining term — it does not account for rate changes, fees, early repayment charges, or any annual overpayment allowance your lender may apply. Always confirm your lender's overpayment rules, and whether an early repayment charge could apply, before making a large overpayment. This is general guidance only and does not constitute financial advice.
A mortgage overpayment is any payment you make above your lender's required minimum monthly payment. It could be a regular extra amount added to every monthly payment, or a one-off lump sum — for example, from a bonus, inheritance, or savings — paid directly off your outstanding balance. Every pound you overpay goes straight toward reducing your capital balance, which means less of your future payments go toward interest and more toward actually paying off the loan.
Because mortgage interest is calculated on your outstanding balance, reducing that balance faster than scheduled means you pay interest on a smaller amount for the rest of the loan — which is why even modest, regular overpayments can add up to a substantial saving over the full term.
When you overpay, most lenders give you a choice of what happens next: you can either keep your monthly payment the same as before and have your mortgage term shortened, or keep your original term and have your monthly payment recalculated downward. Shortening the term is generally the more powerful option for saving interest, because the loan balance is repaid faster and spends less total time accruing interest — but reducing the payment can be the better choice if your priority is lower monthly outgoings rather than finishing early.
Not every lender applies this automatically — some will shorten the term by default unless you specifically request a lower payment instead, while others ask you to choose upfront. It's worth contacting your lender to confirm which option applies and how to switch it if needed.
Many fixed-rate and some discounted-rate mortgage deals include an early repayment charge (ERC) if you repay more of the mortgage than your deal allows within a set period. However, most lenders also build in a penalty-free overpayment allowance — commonly around 10% of the outstanding balance per year — that lets you overpay up to that amount without triggering any charge. This 10% figure is a widely used industry norm rather than a fixed legal standard, so the actual allowance varies by lender and by product, and some deals have no ERC at all (typically standard variable rate and many tracker mortgages).
Always check your original mortgage offer document, your lender's website, or your annual mortgage statement for the exact allowance and ERC percentage that applies to your deal before making a significant overpayment.
A lump sum overpayment is a single, larger payment made at one point in time — for example, putting a bonus or inheritance straight onto your mortgage. A regular overpayment is a smaller, recurring extra amount added to every monthly payment. Both strategies reduce your balance and save interest, but they suit different situations: a lump sum makes sense when you receive a windfall, while regular overpayments are often easier to sustain as part of an ongoing budget and compound their benefit a little each month.
Some borrowers combine both — making small regular overpayments throughout the year and an occasional lump sum — but should keep an eye on their lender's combined annual overpayment allowance if their deal carries an early repayment charge.
Interest on a repayment mortgage is "front-loaded" — in the early years, a much larger share of each monthly payment goes toward interest rather than capital, because the outstanding balance (and therefore the interest charged on it) is at its highest. As the years go by and the balance shrinks, more of each payment chips away at the capital instead. This means an overpayment made early in the mortgage term reduces the balance while it still has many years left to accrue interest, producing a bigger total interest saving than the same overpayment made later, when less time and less balance remain for the saving to compound.
Overpaying effectively gives you a guaranteed "return" equal to your mortgage interest rate, since every pound overpaid stops accruing interest at that rate. Whether that beats saving or investing the same money depends on your mortgage rate compared with realistic after-tax returns elsewhere, how much risk you're comfortable with, your tax-free savings allowances and pension contribution matching, and how important it is to you to keep money accessible for emergencies rather than locked into your home. There's no universally correct answer — it's a personal trade-off between a certain saving and the possibility of a higher but less certain return elsewhere. This is general information only, not financial advice, and you should consider speaking to a regulated financial adviser about your own circumstances.
With a standard overpayment, extra money permanently reduces your mortgage balance — once paid in, it's generally not easy to access again without re-borrowing. With an offset mortgage, your savings are held in a linked account and the balance of that account is offset against your mortgage balance for interest-calculation purposes only, while the cash itself stays accessible to withdraw if you need it. Offset mortgages can suit people who want the interest-saving benefit of their savings without losing access to the cash, though they often come with a different range of available rates and products compared with standard overpayment-friendly mortgages.
Take a mortgage with a £150,000 balance, a 4.5% annual interest rate and 20 years remaining. The standard monthly payment on this loan is roughly £949. Without any overpayment, this mortgage would run its full 240-month (20-year) term and cost around £77,800 in total interest.
Now suppose the same borrower adds £200 a month in overpayments. The mortgage is paid off several years early, and the total interest bill falls substantially compared with the original schedule — the exact new payoff time and interest saved for your own figures are shown live in the calculator above, which runs this same month-by-month calculation automatically.
Most UK lenders let you make overpayments in one of several ways: through your online banking or mobile banking app (often with a dedicated "overpayment" or "make a payment" option), by asking your lender to increase your regular direct debit, or by calling customer service to arrange a one-off lump sum transfer. When you make a payment, check with your lender that it's being applied directly to reduce your capital balance rather than simply held as an advance credit against future monthly payments — the wording and default behaviour can vary by lender.
Fixed-rate deals are the ones most likely to carry an early repayment charge and a capped penalty-free overpayment allowance, because the lender has committed to a set rate for a set period. Standard variable rate (SVR) and most tracker mortgages typically have no early repayment charge at all, meaning you can usually overpay as much as you like, at any time, without restriction. If you're on a fixed deal and want to overpay heavily, it's worth checking whether staying within the annual allowance — or waiting until the deal ends and remortgaging instead — would avoid an unnecessary charge.
This depends entirely on your lender and mortgage product. Many lenders allow overpayments as often as every month through a standing increase to your direct debit, as well as additional one-off lump sums at any time during the year. Others may limit how frequently one-off payments can be made, or require overpayments to be submitted in specific amounts. Your mortgage offer document, online account, or a call to your lender will confirm exactly what your product allows.
Overpaying your mortgage doesn't directly affect your credit score in the way missed or late payments would. Making your payments on time (including any increased regular payment) is reported positively, but there's no separate credit-scoring benefit specifically for paying extra. The real benefit of overpaying is financial — the interest and time saved — rather than any change to your credit file.
If you'd like to look at your mortgage from a different angle, these related calculators can help:
For independent, non-commercial guidance on overpaying a mortgage and on early repayment charges, the following official sources are worth reading alongside this calculator: