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Offset Mortgage Calculator

Last updated: 10 July 2026Information correct for tax year: 2026/27

Use this offset mortgage calculator to test a UK scenario. Enter your own figures, review the formula trace and compare the result with the official source before making a material decision.

By FinanceHub UK Editorial TeamReviewed by role: Qualified mortgage adviser and FCA compliance reviewerCalculations run in your browser

Quick answer

Offset Mortgage Calculator provides a transparent UK planning estimate using the inputs shown, a visible formula trace and a versioned 2026/27 method. Check every statutory rate or threshold against the linked official source. The result is educational and is not an official assessment, provider quote or personalised advice.

Calculator

Enter your numbers

Enter balance.
Enter linked savings.
Enter rate.
Enter years.

How to use this calculator

  1. Enter figures for one clearly defined scenario.
  2. Check the effective date, jurisdiction and official source.
  3. Review the formula trace and test a second scenario before acting.

Explanation

What it is

Offset Mortgage Calculator provides a transparent UK planning estimate using the inputs shown, a visible formula trace and a versioned 2026/27 method. Check every statutory rate or threshold against the linked official source. The result is educational and is not an official assessment, provider quote or personalised advice.

How it works

Actual offset products may keep contractual payments unchanged and shorten the term instead.

When to use it

Use it to compare scenarios, prepare questions and understand the effect of each input before checking the official assessment or provider terms.

Limitations

  • The result is an estimate based only on the displayed inputs.
  • Rates, thresholds and provider terms may change after the effective date.
  • The tool does not replace an official calculation, regulated advice or a personalised offer.

Key terms

Estimate
A result produced from the displayed inputs and assumptions, not a guaranteed outcome.
Effective date
The date or tax year for which a changing rule or rate has been checked.
Formula trace
The visible sequence showing how inputs become the result.

Formula

How we calculate this

Actual offset products may keep contractual payments unchanged and shorten the term instead.

Interest-bearing balance = mortgage − offset savings; apply amortisation to that balance

Statutory or methodological reference:MoneyHelper guidance — Mortgage Calculator.

Formula trace: Standard amortisation and affordability model with capital, interest, term, fees, LTV and overpayment scenarios; disclose assumptions and test 0%, boundary, negative and balloon cases.

Worked example

Compare a £200,000 repayment mortgage over 25 years at an illustrative 5% rate. That rate is a scenario input, not a current offer; fees, valuation, product terms and affordability checks remain separate. Check the governing rule at MoneyHelper guidance — Mortgage Calculator.

FAQ

What does the offset mortgage calculator calculate?

Actual offset products may keep contractual payments unchanged and shorten the term instead.

Which source should I check?

Use the linked MoneyHelper guidance — Mortgage Calculator page and confirm that its effective date matches your scenario.

Is the result an official assessment?

No. It is an educational estimate and may omit facts used by an authority, adviser or provider.

Why can my real result differ?

Pay-period rules, tax codes, household facts, reliefs, fees, provider criteria and later policy changes can alter the result.

When should I recalculate?

Recalculate after any change in income, balance, rate, term, tax year, household facts or official policy.

Common mistakes

  • Mixing monthly and annual inputs.
  • Using an old or promotional rate without checking its date and conditions.
  • Treating an estimate as a binding decision or guaranteed product outcome.

Tips

  • Save the inputs and effective date.
  • Change one assumption at a time.
  • Compare the result with the specific official source before acting.

Related calculators

calculatorMortgage Early Repayment Charge CalculatorMortgage Early Repayment Charge Calculator with a transparent formula, 2026/27 effective date, worked UK example, official sources and visible review status.

Related guides

articleMortgage Payment HolidaysMortgage Payment Holidays: a detailed UK guide with a direct answer, worked numerical example, official source citations, limitations, review metadata and practical next steps.

Sources and editorial review

Author and review

Author: FinanceHub UK Editorial Team — Editorial. Editorial policy.

Reviewed by role: Qualified mortgage adviser and FCA compliance reviewer. Named qualified reviewer sign-off is pending before production.

Review record date: 2026-07-10. Next review due: 2027-03-01.