About Mortgage Overpayment Calculator

Our Mission

The Mortgage Overpayment Calculator is a free tool designed to help UK homeowners calculate complex overpayment restrictions, such as overpaying based on the remaining balance, rather than a set amount every year.

We believe that financial clarity empowers better decision-making. By providing accurate, easy-to-understand calculations, we help homeowners see exactly how overpayments can reduce their mortgage term and save thousands in interest payments.

Why We Built This Calculator

There are numerous mortgage calculators out there but they only give homeowners a view on much they could save in basic scenarios. They don't cover:

• How much can I overpay if I get an allowance of 10% on the remaining balance each year?
• How much can I save if I remortgage to a lower rate in the future?
• How much can I save if I overpay by a lump sum when my fixed deal ends?

We created this calculator to answer these questions clearly and quickly, without requiring financial expertise or complex spreadsheets.

How It Works

The calculator uses standard mortgage mathematics to project how overpayments affect your mortgage balance over time.

The calculator supports two overpayment modes:

• Percentage of Remaining Balance: Your overpayment amount adjusts each year based on your current balance (gradually decreasing over time)
• Percentage of Original Balance: Your overpayment amount stays fixed throughout the mortgage term

Who This Tool Is For

The calculator is designed for:

• Current homeowners looking to understand the benefits of overpaying their mortgage
• First-time buyers exploring whether overpayments fit their financial strategy
• Remortgage customers considering overpayment options on their new deal
• Financial planners helping clients model different repayment scenarios

What Makes Us Different

• Models Real-World Scenarios: Choose between remaining balance or original balance calculations, add in remortgage points, lump sums, and more.
• Visual clarity: Interactive charts show your balance reduction over time
• Year-by-year breakdown: See detailed repayment schedules for every year
• 100% free: No registration, no subscriptions, no hidden fees
• Privacy-focused: Your data stays on your device

Important Disclaimers

While we strive for accuracy, this calculator provides illustrative estimates only and does not constitute financial advice.

Key limitations:

• Results may not account for early repayment charges imposed by your lender
• Most lenders cap annual overpayments at 10% of the outstanding balance
• Variable or tracker mortgage rates may change over time
• Your lender's specific terms and conditions may differ from our assumptions

Always verify calculations with your mortgage lender and consult a qualified financial advisor before making overpayment decisions.

See our Disclaimer for complete information.

Data Privacy

Your privacy is important to us. The calculator processes all mortgage data entirely in your web browser - we do not store, transmit, or have access to your mortgage details.

We use cookies for analytics and advertising (with your consent) to help us improve the calculator and keep it free. You can learn more in our Privacy Policy and Cookie Policy.

Our Commitment to Accuracy

We take accuracy seriously. The calculator uses standard financial mathematics:

• Standard annuity formula for monthly payment calculations
• Annual overpayment application (applied at the end of each year)
• Compound interest calculations based on remaining balance
• Newton's method for reverse-engineering interest rates from monthly payments

If you notice any errors or have suggestions for improvement, please contact us using the details in the footer.

Learn More

We've created a series of guides to help you understand mortgage overpayments better:

• How Mortgage Overpayments Work →
• Is It Better to Overpay Your Mortgage? →
• The 10% Overpayment Rule Explained →
• How Much Interest Can You Save? →