UK mortgage calculators
Mortgage Guides
Use these decision guides alongside the calculators. They explain what the result can and cannot tell you, the figures to gather and the checks to make before contacting a lender or broker.
Mortgage Overpayment Calculator
Use your own figures to explore this mortgage scenario.
Overpay Mortgage or Save Calculator
Use your own figures to explore this mortgage scenario.
Remortgage Break-Even Calculator
Use your own figures to explore this mortgage scenario.
Mortgage Repayment Calculator
Use your own figures to explore this mortgage scenario.
Mortgage Rate Shock Report
Use your own figures to explore this mortgage scenario.
Interest-Only vs Repayment Calculator
Use your own figures to explore this mortgage scenario.
Mortgage Fee vs Lower Rate Calculator
Use your own figures to explore this mortgage scenario.
Sources and review standard
Calculations are independently implemented illustrations and were reviewed on 4 September 2026. We check factual boundaries against MoneyHelper's mortgage cost guidance, FCA consumer mortgage information and relevant lender documentation. Rates and product terms are never presented as live offers.
A practical decision record
- State the question and the date of the comparison.
- Record each input and where it came from.
- Run a base case and at least one adverse rate or cost scenario.
- Write down what the model omits, including tax, access to cash or lender-specific rules.
- Check the proposed action against the mortgage terms and qualified advice where needed.
How to challenge a result
Recalculate the monthly payment using the same balance, rate and term, then check fees and comparison period separately. If a lender's result differs, ask whether it uses daily interest, a different completion date, fees added to the balance or another repayment convention.
Practical worksheets and case studies
Mortgage Calculator Input Checklist
Collect current balance, term, rate, fees and decision context before relying on a mortgage illustration.
Mortgage Overpayment Case Study
Follow a fictional overpayment illustration and the contract, liquidity and verification checks around it.
Remortgage Break-Even Case Study
Examine a fictional lower-rate deal, switching fees and the comparison horizon before drawing a conclusion.
Interest-Only Mortgage Payments and Repayment Guide
Calculate an illustrative interest-only payment, compare repayment structure and test the evidence behind a capital repayment strategy.
Mortgage Stress-Test Worksheet
Build a rate, term and fee scenario table and define when lender or adviser review is required.
Editorial responsibility
Published by Acerville Sparks Limited. Software assists research, drafting and automated formula testing. Primary sources, assumptions and limitations are shown so readers can inspect the work. No independent mortgage professional or financial adviser review is claimed. Reviewed 4 September 2026.