Useful next calculations
Rates and 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.
| Band or figure | Rate |
|---|---|
| Payment model | fixed monthly repayment |
| Rate | entered by you and held constant |
| Early repayment charge | not modelled |
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 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.
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.
| Input | Value |
|---|---|
| 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.
Method & assumptions
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.
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.