Mortgage overpayment calculator

What your result means

Explore how paying extra could clear a repayment mortgage sooner and reduce interest. The comparison keeps the original regular payment unchanged after a one-off overpayment.

Compare scenarios by changing one input at a time. The glossary explains the technical words used on this page.

New estimated payoff time

How long the remaining balance takes to reach zero with the extra payments entered. The last payment can be smaller than a normal payment.

Time saved

The difference between the modelled payoff times with and without overpayments.

Interest saved

Interest in the no-overpayment calculation minus interest with overpayments. It does not deduct any early repayment charge.

Total interest after overpaying

Interest remaining to be paid after the one-off payment and regular extra payments. It is not the total cash needed to repay the mortgage.

Methodology: how the calculation works

This is a month-by-month amortisation model. It compares the same repayment mortgage twice: once without extra payments and once with them.

1. Calculate the regular capital-and-interest payment from the starting balance, annual rate and remaining months. The annual percentage is divided by 100 and 12.
2. Subtract the one-off overpayment before the first month’s interest is charged. The regular payment is still based on the original balance.
3. For each month, add interest on the outstanding balance, then deduct the regular payment plus the monthly overpayment. Cap the final payment at the amount still due.
4. Repeat until the balance is cleared, then compare total interest and the number of payments against the no-overpayment case.

The assumptions behind your estimate

• The entered rate stays unchanged for the full term, not just an initial deal period. The pre-filled rate is an illustration, not a live offer.
• Payments occur at the end of each month. Daily interest, irregular dates, missed payments and changes of rate are not modelled.
• Money is displayed to the nearest pound. Totals use unrounded calculations, so multiplying the displayed payment by the number of months can differ from the displayed total.
• Extra monthly payments continue until the loan is cleared. The one-off payment happens immediately, not at a future date.
• Overpayments reduce the time taken, not the regular required payment. No lender allowance, charge or change in payment arrangement is applied.

Two simple worked examples

Both examples start with £200,000 outstanding at 4.75% over 25 years. There is no one-off payment. The extra monthly payment is the only change.

A closer look: regular payments and a lump sum

Compare four ways of paying the same mortgage. The £10,000 lump sum is additional money paid towards the debt, not a discount or a fee.

On a small screen, swipe the table sideways to see every figure.

The earlier capital is repaid, the less time it attracts interest in this constant-rate model. Combining a lump sum and regular extra payments commits more of your money; the interest saving alone does not decide whether that is right for you.

Examples use the stated assumptions and the existing calculator’s rounding. They are illustrations, not product offers, personalised recommendations or guarantees.

What the estimate does not include

• Any early repayment charge, annual overpayment allowance or lender-specific restriction. Check these before paying extra.
• Rate changes, missed payments, daily-interest timing and a lender reducing your regular payment after a lump sum.
• The effect on accessible savings, other debts, household spending or income. This is not an affordability assessment.

Mortgage overpayment glossary: the words explained

Plain-English definitions of the finance, calculation and technical terms used on this page. Dotted links take you directly to the relevant definition.

Affordability / affordability check

An assessment of whether payments fit income, spending and other financial commitments. This tool does not perform that assessment.

Amortisation

Paying off borrowing gradually through regular payments covering interest and some capital. With a constant rate and payment, the interest share reduces as the balance falls.

Annual / monthly rate

Annual means per year; monthly means per month. A monthly rate is not interchangeable with an annual rate. The methodology explains this tool’s conversion.

APRC (annual percentage rate of charge)

A mortgage cost-comparison percentage including interest and applicable fees over the full term using specified assumptions. It is not the interest-rate input.

Arrangement fee / product fee / lender fee

A charge for setting up or providing a financial product, separate from interest. A percentage fee needs a stated base amount.

Balance / outstanding balance

The money held in an account, or the amount still owed on a loan, at a given time.

Broker / credit broker / broker fee

A business that introduces customers to finance providers or helps arrange finance, rather than lending the money itself. A broker fee is a charge for that service.

Capital / principal / amount borrowed

The original money borrowed, separate from interest. Paying back capital reduces the outstanding loan.

Credit / finance / borrowing

Money made available to borrow and repay later, usually with interest or charges.

Credit check / credit status / credit history

A check of information about past borrowing and repayments, and the financial record it describes. Providers may use it when assessing an application.

Deposit

Money contributed towards a purchase without borrowing it. Here it reduces the amount financed.

Early repayment charge / early settlement charge

A charge that may apply when some or all of borrowing is repaid ahead of schedule. The agreement sets out any conditions and limits.

Eligibility / lender criteria

The requirements a provider sets for an application. A calculated repayment does not show that an applicant qualifies.

Estimate / illustration / projection

A result based on stated inputs and assumptions, not a promise of what will happen or a provider’s offer.

Financial Conduct Authority (FCA) / authorised and regulated

The UK financial-services regulator named in the site footer. Authorisation gives a firm permission for specified activities; regulation means it must follow the applicable rules.

Fixed rate / deal period

A fixed rate stays unchanged for an agreed period. That period may be shorter than the whole loan term.

Insurance

Cover bought for specified losses or events, subject to the policy’s conditions. Its price is not automatically included here.

Interest / interest rate

Interest is a charge for borrowing or a return paid on savings. The rate expresses it as a percentage over a stated period.

Interest-only

Regular payments cover interest without paying back the original loan. The capital must be repaid separately, usually at the end.

Legal fees

Charges for legal work involved in a purchase or finance arrangement.

Lender / provider

The organisation supplying a loan or financial product and setting its terms.

Loan-to-value (LTV)

The loan as a percentage of the property value: loan ÷ value × 100. This tool uses the values entered, not a lender’s valuation.

Methodology

The calculation method, steps and assumptions behind an estimate.

Mortgage / secured borrowing / security

A loan backed by an asset such as property. Security is the asset a lender may use to recover unpaid borrowing through the applicable legal process.

Overpayment / one-off payment / lump sum

An amount paid in addition to the regular amount due. A one-off payment or lump sum is paid once; a monthly overpayment repeats.

Payoff time / time saved

The time until the modelled loan is cleared. Time saved is the difference compared with the no-overpayment calculation.

Property price / property value

Price is the amount paid; value is an assessment of what a property is worth. They can differ.

Quote / finance offer

Proposed prices and conditions from a provider. It is different from an illustration and may still depend on checks or conditions.

Remortgage

Replacing an existing mortgage on a property with a new one, commonly from a different lender.

Repayment / monthly payment

Money paid back to a lender. A capital-and-interest payment covers interest and reduces the amount borrowed. An interest-only payment does not reduce it.

Repossession

The legal process by which a lender can take possession of an asset after repayments are not kept up. It may be sold to recover money owed.

Rounding / unrounded

Shortening a number for display. An unrounded calculation keeps the more precise value when working out totals.

Term / repayment period

The length of time over which the calculation runs. For borrowing, it is the planned repayment period, not necessarily the length of an introductory rate deal.

Total interest

All the interest in the calculation, excluding the original loan and any separately stated fees.

Total repayable / total payable

The combined amounts counted by this tool. Read the results explanation to see whether fees, deposits or a final capital payment are included.

Upfront fee / upfront payment

Money paid at the start instead of added to the loan or paid at the end.

Valuation / valuation fee

An assessment of what a property is worth and any charge for it. This is not a detailed survey of its condition.

Frequently asked questions