mortgageen-GB · Local rules
UK mortgage overpayment calculator
Model overpayments against a UK repayment mortgage. SDLT, LBTT and LTT remain separate transaction-cost estimates, not part of the loan payment.
Methodology
Repayment estimate with SDLT shown separately for England and Northern Ireland.
How to read this
A payment is only one part of the decision.
The first years of a mortgage usually carry more interest than principal. The local rules panel keeps taxes, insurance, and market conventions separate so you can see what is assumed.
View the amortization tableCompare plans
See the cost of paying extra
| Scenario | Total interest | Payoff time | Interest saved |
|---|---|---|---|
| Base plan | £437,969 | 30y 0m | £0 |
| +300/month | £302,096 | 22y 0m | £135,874 |
Lender overpayment allowances, annual caps and early-repayment charges are not modelled. Confirm the current mortgage contract before paying extra.
Mortgage scenarios
Calculations for the way you plan to repay
Use the controls above instead of relying on a generic payment estimate. Each option changes the cash flow or balance shown in the results.
Interest-only mortgage calculator with extra payments
Select Interest-only to estimate the periodic interest payment and remaining principal. Add an extra payment to model principal reductions, subject to your lender's limits and early-repayment charges.
Mortgage extra-payment calculator based on your current balance
Enter the balance you still owe as the loan amount, then compare the base plan with an additional monthly principal payment. The table shows estimated interest saved and payoff time.
UK mortgage overpayment calculator
Use the extra monthly payment field to compare overpayment savings. Check the mortgage agreement separately for annual allowances and any early repayment charge.
First six periods
Amortization preview
| Period | Payment | Principal | Interest | Balance |
|---|---|---|---|---|
| 1 | £2,417 | £342 | £1,875 | £359,458 |
| 2 | £2,417 | £344 | £1,872 | £358,914 |
| 3 | £2,417 | £347 | £1,869 | £358,367 |
| 4 | £2,417 | £350 | £1,866 | £357,817 |
| 5 | £2,417 | £353 | £1,864 | £357,264 |
| 6 | £2,417 | £356 | £1,861 | £356,708 |
Sources and assumptions
Transparent by design.
Loan payment uses the selected country compounding convention. Taxes and recurring costs are separate estimates; local rates, insurance quotes, closing costs and lender fees may not be included.
Calculation data: GB-2026.08 · effective from 2025-04-01 · reviewed 2026-08-25.
Applies to: Repayment or interest-only illustrations for England, Northern Ireland, Scotland and Wales.
Formula: Monthly nominal-rate amortization with SDLT, LBTT or LTT calculated separately.
Rounding: Calculations retain precision; displayed currency is rounded to whole pounds.
Included: Principal, interest, optional extra payments and the selected transaction-tax estimate.
Excluded: Lender fees, insurance, conveyancing, valuation, broker fees and early-repayment charges.
Official source: HMRC SDLT residential rates
Open official source ↗
Effective from 2025-04-01; reviewed 2026-08-25.
This calculator is educational only and is not a loan offer, tax opinion, legal advice or financial advice. Confirm the current rule with the lender, tax authority, notary or conveyancer before relying on it.
Methodology and local rules
Built to explain the assumptions.
England / Northern Ireland is selected for the transaction-tax context. The displayed loan uses the local currency and separates loan repayment from transaction costs. Country rules are versioned and should be checked against the lender and authority at the time of purchase.
Source: HMRC SDLT residential rates · Effective from 2025-04-01 · Reviewed 2026-08-25. This is an estimate; confirm the deed date, eligibility, lender terms and local authority before relying on it.
Read the full methodology (English)FAQ
What this estimate does and does not include.
Open a question for the full answer. The first answer is shown by default.
Is this a mortgage offer?
No. This is an illustrative estimate, not a loan offer, tax opinion, legal advice or financial advice.
What is included in the monthly payment?
The main result includes principal and interest. US users may add property tax, home insurance, HOA fees and flood insurance. Transaction taxes and other closing costs are shown separately when supported.
Why can my lender quote be different?
Lenders may use different compounding, payment dates, daily-interest rules, fees, insurance premiums, product rates and rounding. Use the estimate for comparison and confirm the final figures with your lender.
How do extra payments affect the mortgage?
When your agreement allows extra principal payments, they can reduce the balance sooner, lower later interest and shorten the payoff period. Check for overpayment limits or early-repayment charges.
Do local taxes vary?
Yes. Transfer taxes, property taxes, insurance and eligibility rules vary by country, state, province, municipality or autonomous community and may change after our review date.
Is my calculator data stored?
Calculations run in your browser. A share link places the selected calculation inputs in the URL, so treat that URL as information you have chosen to share.