Mortgage overpayment calculator how much could you save?

A mortgage overpayment calculator is a tool that shows you the effect of paying more than your required monthly mortgage repayment. Rather than waiting years to see the impact on paper, you can enter your outstanding balance, your remaining term, and how much extra you'd like to pay, to get an instant picture of the difference it could make.

Overpaying works because your mortgage interest is calculated on your outstanding balance. Every time you pay down that balance faster than scheduled, you reduce the amount interest is charged on for the rest of the term, which can mean paying less interest overall and potentially clearing your mortgage sooner.

A calculator gives you an estimate rather than an exact figure, since your actual saving depends on your interest rate, whether it's fixed or variable, and your lender's specific overpayment terms. It's a useful starting point before you make any changes to your repayments.

When you take out a mortgage, your lender works out a monthly repayment that clears the balance, plus interest, by the end of your agreed term. Every payment you make is split between interest and paying down the capital you borrowed.

An overpayment is any amount above this required monthly repayment. You can usually make overpayments in two ways:

• Regular overpayments - adding a set amount to your monthly repayment, which most lenders let you set up and change at any time
• Lump sum overpayments - paying a one-off amount, for example from a bonus, inheritance, or savings

Most lenders apply overpayments in one of two ways: either reducing your monthly repayment while keeping your term the same, or keeping your monthly repayment the same and shortening your term. Reducing the term rather than the payment usually saves more in total interest, since the balance is cleared faster, but check with your lender which option they offer and whether you can choose between them.

How much you could save by overpaying depends on three things: how much you overpay, how early in the term you make the overpayment, and your current interest rate. As a general rule, the earlier you overpay and the more you pay off, the more interest you avoid over the life of the mortgage.

This is because interest is calculated on your outstanding balance. Reducing that balance earlier means less interest accrues on it for longer, which compounds over the remaining years of your mortgage. A lump sum overpayment made in year one of a 25-year mortgage will typically make a bigger difference to your total interest than the same overpayment made in year twenty, when there's less time left for the reduced balance to make an impact.

Because the exact saving depends on your interest rate and whether you have a fixed, tracker, or variable deal, it's best to use the calculator with your own figures and speak to an advisor to understand what a realistic saving might look like for your specific mortgage.

Your home may be repossessed if you do not keep up repayments on your mortgage or any other debt secured on it.

Most fixed and tracker mortgage deals let you overpay up to a set percentage of your outstanding balance each year, commonly 10%, without any penalty. Overpay beyond that limit, and many lenders will charge an early repayment charge on the excess amount.

For example, if your outstanding balance is £200,000 and your lender allows a 10% annual overpayment allowance, you could pay off up to £20,000 that year without triggering a charge. Overpaying by more than your allowance in a single year could mean a charge applies to the amount above the limit.

Your overpayment allowance and any early repayment charge terms are set out in your original mortgage offer. If you're not sure what applies to your deal, check your paperwork or ask your lender directly before making a large overpayment.

• Standard variable rate mortgages usually have no overpayment limit or early repayment charge
• Fixed and tracker deals often cap penalty-free overpayments at around 10% a year
• Early repayment charges typically reduce the longer you've been on your current deal

Overpaying your mortgage isn't always the best use of spare money, and the right choice depends on your wider financial picture.

Overpaying tends to make more sense if:

• You have no higher-interest debts, such as credit cards or personal loans, outstanding
• You already have an emergency fund covering a few months of essential costs
• Your mortgage interest rate is higher than the return you'd realistically get from savings after tax

Saving or investing instead may make more sense if:

• You might need access to the money in the next few years, since money paid into your mortgage isn't easily accessible again
• You have an employer pension contribution you're not fully using, which adds value on top of your own contribution
• Your mortgage rate is relatively low compared with what you could realistically earn elsewhere

There's no single right answer, and many people do a mix of both. An advisor can look at your full circumstances, including your mortgage, savings, and other debts, to help you weigh up the options.

If you're worried about managing your mortgage alongside other debts, MoneyHelper offers free, independent guidance at moneyhelper.org.uk or on 0800 138 7777.