Example result based on the prefilled values.
Current Payment
£1,238.20
Payment With Monthly Overpayment
£1,438.20
Payoff Term
15.00 years 7.00 months
Months Saved
54.00
Interest Saved
£29,062.14
Continue your plan
Useful next calculations
Rates & sources
Illustrative repayment-mortgage comparison using the rate, remaining term, and regular or one-off overpayments entered. Check your lender’s allowance and any early repayment charge before paying more.
Source: MoneyHelper — should you pay off your mortgage early? — check the linked guidance and any live quote before acting.
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
Current 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.
Payment With Monthly Overpayment
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.
Payoff Term
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.
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.
Method & assumptionsAuthoritative sources
This calculator compares a baseline repayment projection with a plan that adds the monthly and one-off overpayments you enter. It keeps the calculated contractual repayment constant and applies the one-off amount before the monthly projection; the payoff term and interest saving are therefore estimates rather than instructions to your lender. A lender may instead reduce your required payment, credit an overpayment at a different point, or apply product-specific rules.
The projection assumes a constant interest rate and does not model early repayment charges, rate changes, payment holidays, offsets or fees. Check your lender's overpayment allowance, any early repayment charge and how it will apply a lump sum before paying.
Official references
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.
Go deeper — 1 guide reference this calculator
Frequently asked
Use arrow keys to navigate items, Enter or Space to expand/collapse.