Remortgage Calculator

What Information Do You Need to Use the Calculator?

To get an accurate estimate, you will need three figures to hand:

• Your remaining mortgage balance – the amount you still owe your current lender.
• Your estimated property value – used to calculate your loan-to-value (LTV) ratio, which affects the rates available to you.
• Your preferred mortgage term – how many years you want the new deal to run.

Once you have those, the calculator will show your estimated monthly repayment, total interest over the term, and how your payments compare to your existing deal.

How the Remortgage Calculator Works – The Formula Explained

Monthly mortgage payments for a fixed-rate loan are calculated using the standard amortisation formula:

M = P × [r(1 + r)ⁿ] / [(1 + r)ⁿ − 1]

Where:

• M = monthly repayment amount
• P = principal loan amount (your remaining mortgage balance)
• r = monthly interest rate (your annual rate divided by 12)
• n = total number of monthly payments (years remaining × 12)

This is the same formula used by UK lenders when setting your monthly direct debit. The calculator above runs this instantly for any combination of balance, rate and term you enter.

A Step-by-Step Calculation Example

To see how this works in practice, assume a homeowner wants to remortgage a remaining balance of £200,000 over a 25-year term at a fixed annual interest rate of 4.5%.

Step 1 – Convert Annual Figures to Monthly

Divide the annual interest rate by 12 to get the monthly rate:

r = 0.045 / 12 = 0.00375

Multiply the term in years by 12 to get the total number of payments:

n = 25 × 12 = 300 months

Step 2 – Calculate the Payment Factor

Compute (1 + r)ⁿ:

(1 + 0.00375)³⁰⁰ = 3.06979

Substitute into the formula:

0.00375 × 3.06979 / (3.06979 − 1) = 0.01151 / 2.06979 = 0.00556

Step 3 – Work Out Your Monthly Repayment

Multiply the principal by the factor:

M = £200,000 × 0.00556 = £1,111.66 per month

How Your Payments Change Over Time

In the early years, most of each monthly payment goes toward interest. Over time, the balance of principal reduces, so the interest portion of each payment falls and more of your payment clears the actual debt. This is why the total interest cost over a 25-year term can be significantly higher than the original loan amount.

Example Results at a Glance

Factors That Affect Your Remortgage Savings

Looking at the interest rate alone does not give you the full picture. These three factors can significantly change how much you actually save. For a full breakdown of remortgage costs, see our guide to remortgage fees.

Loan-to-Value (LTV) Ratio

Your LTV is calculated as:

LTV = (Loan Amount / Property Value) × 100

Lower LTV brackets unlock meaningfully lower interest rates. Moving from an 80% LTV to a 75% or 70% LTV bracket can reduce the rate available to you by 0.25% or more, which compounds into a substantial saving over a long term. The calculator uses your property value to show which LTV band you fall into.

Product and Arrangement Fees

Lenders frequently charge a booking or arrangement fee, which is often around £999, though it can be higher on some products. A deal with a lower headline rate but a £999 fee may cost more overall than a slightly higher rate with no fee. The calculator factors fees into the total cost comparison so you can see the genuine saving, not just the monthly figure.

Early Repayment Charges (ERCs)

If you leave your current mortgage before the fixed term ends, your lender may charge an ERC, typically 1% to 5% of your remaining balance. On a £200,000 mortgage, that could be anywhere from £2,000 to £10,000. It is worth checking your current deal’s ERC schedule before committing to a switch. Our page on when to remortgage explains how to time your switch to avoid unnecessary penalties.

Who Is This Calculator For?

This tool is suitable for most standard residential remortgage scenarios, including:

• Switching to a better rate at the end of a fixed or tracker deal
• Releasing equity from your home for home improvements, a deposit on another property, or other purposes
• Borrowing additional funds against your property. See our guide on remortgaging for home improvements
• Consolidating existing debts into your mortgage to reduce monthly outgoings
• Buy-to-let remortgages, where different affordability rules apply

If you are unsure which scenario applies to you, what is remortgaging and how does it work? is a good starting point.

What to Do Once You Have Your Estimate

Our online platform allows you to compare remortgage deals from lenders across the UK, giving you access to real-time information on the best available rates. Once you have identified a deal that fits your needs, our team of specialists is here to offer tailored support. We take the time to understand your specific financial circumstances and long-term objectives, helping you select the most suitable remortgage solution.

If you are unsure or require guidance, do not hesitate to get in touch. We are here to simplify the process, remove any confusion, and help you secure a remortgage that aligns with your financial goals.

It is also worth understanding how long a remortgage takes so you can plan your application at the right time.