Remortgage Calculator

UK mortgage comparison tool

Compare the estimated monthly payment on your current mortgage with a proposed new deal. Use the result as a starting point, then check fees, early repayment charges and total borrowing costs before making a decision.

Quick answer A lower interest rate does not automatically make a remortgage cheaper overall. The mortgage balance, repayment type, term, product fee, legal or valuation costs and any early repayment charge can all change the true cost.
  • Reviewed by Attach Planet
  • Last reviewed: 16 July 2026
  • Illustrative figures only

Illustrative payment comparison

Compare your monthly mortgage payments

Enter the figures for your current mortgage and a proposed new deal. The result helps you compare monthly payments before you account for fees, charges and changes to the mortgage term.

Current mortgage
Proposed mortgage

How to use the remortgage calculator

  1. 1Enter your current mortgageAdd the outstanding balance, current interest rate, remaining term and repayment type.
  2. 2Add the proposed dealUse the balance, rate, term and repayment type shown in the new mortgage illustration.
  3. 3Compare, then check the full costReview the monthly difference, but also calculate fees, charges and the total interest payable.

What the result means

The calculator estimates the monthly payment for both mortgages and shows the difference. A monthly reduction means the proposed payment is lower on the figures entered. A monthly increase means it is higher.

The result does not say whether a mortgage is suitable for you. A longer term can reduce the monthly payment while increasing the amount of interest paid over the life of the mortgage. Adding a product fee to the loan also means paying interest on that fee.

How the calculation works

For a capital repayment mortgage, the calculator uses the standard monthly amortisation formula:

Monthly payment = P × r ÷ (1 − (1 + r)−n)

Here, P is the mortgage balance, r is the monthly interest rate and n is the number of monthly payments. For an interest-only mortgage, the estimated payment is the balance multiplied by the annual rate and divided by 12.

Costs to check before you remortgage

  • Existing-lender chargesCheck the early repayment charge, mortgage exit fee and the date your current deal ends.
  • New-deal feesInclude product or arrangement fees, booking fees and any fee added to the mortgage balance.
  • Professional costsAllow for valuation, legal, conveyancing and mortgage advice or broker fees where applicable.
  • IncentivesAccount for cashback, free valuation or legal work, while checking the conditions attached.
  • Term and total interestCompare the total amount repayable, not only the initial monthly payment.
  • Repayment flexibilityCheck overpayment limits, portability, payment holidays and other features you genuinely need.
Important: If you are struggling with mortgage payments, contact your lender promptly. You can also read the FCA’s guidance on support for mortgage borrowers.

When might remortgaging be worth investigating?

It may be worth comparing options when your current fixed or discounted period is approaching its end, when your property value or mortgage balance has changed enough to improve your loan-to-value band, or when you need different features from your mortgage. It can also be sensible to ask your existing lender about a product transfer before applying elsewhere.

Start early enough to compare the whole market available to you, but check how long a new offer will remain valid and whether leaving your current deal early would trigger a charge.

Remortgage calculator FAQs

What is remortgaging?

Remortgaging means replacing the mortgage on a property with a new mortgage, usually with a different lender. Moving to another product with the same lender is commonly called a product transfer.

Does a lower monthly payment mean the new mortgage is cheaper?

Not necessarily. A longer term can reduce the monthly payment but increase total interest. Product fees, legal costs, valuation fees and early repayment charges can also outweigh an apparent monthly saving.

Can I use this calculator for an interest-only mortgage?

Yes. Select interest only for either mortgage. The result estimates monthly interest and does not include any separate amount you may need to save or invest to repay the capital at the end of the term.

Can I compare part repayment and part interest-only mortgages?

Yes. Select the part repayment, part interest-only option and enter the interest-only portion. That amount cannot be greater than the total mortgage balance.

Can I remortgage before my current deal ends?

You may be able to, but your existing lender could charge an early repayment charge or exit fee. Compare those costs with the potential benefit and check the exact terms of your current mortgage.

Is this calculator financial advice?

No. It is an educational, illustrative tool. Mortgage eligibility, affordability and suitability depend on your circumstances and the lender’s criteria. Consider regulated mortgage advice if you need a personal recommendation.

Further independent guidance

Attach Planet does not provide mortgage advice or arrange mortgages. Calculator results are estimates based only on the information entered and may differ from a lender’s illustration. Check all figures with the relevant lender or a suitably authorised mortgage adviser before acting.