Months Saved
53.00
Interest Saved
£28,224.45
Normal Payment
£1,238.20
Rates & sources
Standard amortisation formulas used across UK lenders. Interest rates move daily — confirm with your lender or broker.
Source: Bank of England — Statistics — figures refreshed at the start of each tax year.
When to use this calculator
- Before comparing lenders, brokers, or repayment options.
- When you want to test how a different deposit, rate, or term changes affordability.
- When you need a quick estimate before using a formal quote or agreement in principle.
- When you are stress-testing your budget against a potential rate rise to see the impact on monthly payments.
- When you want to understand the full cost of borrowing — not just the monthly figure — before you commit.
Example: adding a small overpayment to a standard mortgage
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
Outstanding mortgage
£200,000
Current rate
5.1%
Remaining term
22 years
Monthly overpayment
£250
Even a modest overpayment can remove years from the term. The decision becomes clearer once you compare that saving with other uses for the same cash.
How to read your results
Months Saved
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Interest Saved
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Normal Payment
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Method & assumptionsAuthoritative sources
This calculator models the effect of making regular additional payments on top of your contracted monthly mortgage repayment. It assumes a constant interest rate for the full projection period and applies overpayments immediately to reduce the outstanding principal at the end of each month. In practice, the timing of when overpayments are credited can vary by lender — some apply them at the end of the month, others at the point of receipt, which slightly affects total interest saved. The figures shown do not account for any early repayment charges that may apply if overpayments exceed your lender's permitted annual limit. Always verify your overpayment allowance before committing to additional payments above the standard contractual amount.
Common mistakes
- !Mixing up loan amount and property value, which can distort affordability and LTV.
- !Using a headline rate but forgetting fees, insurance, taxes, or repayment type.
- !Testing only one term length instead of comparing the payment and total cost together.
- !Forgetting that a repayment mortgage and an interest-only mortgage produce very different monthly figures and total costs.
- !Not accounting for the impact of a rate revert after an introductory fixed period ends, which can sharply increase payments.
What to do next
- Run a second scenario with a higher rate or shorter term so you can see the downside clearly.
- Compare the result with an affordability or overpayment calculator before applying.
- Use the related guides below to understand trade-offs before you request live quotes.
- Note down the monthly payment and total interest for your two or three strongest scenarios so you have a clear comparison ready when you speak to a broker.
- Check whether making a modest overpayment each month would reduce total interest significantly — run the overpayment calculator next to find out.
Frequently asked
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End-of-article next steps
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