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 |
| Fixed Rate (%) | 5% |
| Variable Rate (%) | 5% |
| Term (Years) | 25 years |
After entering these figures, review fixed, variable and difference together rather than in isolation. Then rerun the tool with one input adjusted.
How to read your results
Fixed
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.
Variable
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.
Difference
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 compares the total cost of a fixed-rate mortgage against a variable or tracker mortgage over a chosen time horizon. For the fixed rate, the monthly payment and total cost are straightforward to calculate and remain constant throughout the comparison period. For the variable option, the calculator uses the current rate to project costs, with an optional rate-rise scenario so you can stress-test your budget. The comparison period is important: if it does not align with the end of a fixed deal, exit costs may apply. The tool does not model rate changes dynamically over time, and actual tracker costs will depend entirely on how the central bank base rate moves. This is a planning tool, not a guarantee of future costs.
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
Use arrow keys to navigate items, Enter or Space to expand/collapse.