Continue your plan
Useful next calculations
Rates & sources
Standard amortisation formulas used across UK lenders. Interest rates move daily — confirm with your lender or broker.
Source: Bank of England — Statistics — check the linked guidance and any live quote before acting.
When to use this calculator
- Before comparing mortgage products, brokers or repayment types.
- When you want to test how a different deposit, rate or term changes the payment.
- When you need a quick estimate before using a formal illustration or agreement in principle.
- When you are stress-testing your budget against a higher rate.
A realistic UK planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
| Input | Value |
|---|---|
| Loan Amount (£) | £200,000 |
| Interest Rate (%) | 5% |
| Original Term (Years) | 25 years |
| New Term (Years) | 25 years |
After entering these figures, review interest saved and new monthly together rather than in isolation. Then rerun the tool with one input adjusted.
How to read your results
Interest Saved
The figure produced by this output for the inputs you entered. Change one variable at a time if you want to see what drives it.
New Monthly
The figure produced by this output for the inputs you entered. Change one variable at a time if you want to see what drives it.
Method & assumptionsAuthoritative sources
This calculator models the effect of making one or more overpayments on a standard capital repayment mortgage. It recalculates the full amortisation schedule from the point of each overpayment, showing how the reduction in principal leads to lower interest charges in every subsequent month. The interest saving figure represents the cumulative difference between the original schedule and the revised one. The calculation assumes the interest rate remains constant throughout the remaining term, which will not be the case if you are on a tracker or variable rate product. It also assumes the lender applies the overpayment immediately to the principal rather than holding it in a suspense account — practices vary, so confirm the arrangement with your lender.
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.
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.
- Note the monthly payment and total interest for your strongest scenarios before you speak to a broker.
- Check whether a modest overpayment would reduce total interest — use the overpayment calculator next.
Frequently asked
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