Useful next calculations
Rates and 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 worked example
These are the example figures the calculator opens with.
| Input | Value |
|---|---|
| Loan Amount (£) | £200,000 |
| Annual Interest Rate (%) | 4.5% |
| Term (Years) | 25 years |
For those figures the calculator returns:
- Monthly Payment: £1,111.66
- Total Repaid: £333,499.49
- Total Interest: £133,499.49
- Principal: £200,000.00
Method & assumptions
A mortgage amortisation schedule breaks down every monthly payment across the full loan term into its two components: the interest charge and the capital repayment. The calculation uses the standard annuity formula applied to your loan amount, annual interest rate, and term in months. Each month's interest is calculated on the outstanding balance at the start of that month, which reduces by the capital portion of that payment. The schedule assumes a constant interest rate for the entire term — a simplification that is useful for illustration but rarely reflects reality, as most UK borrowers remortgage every two to five years. The tool does not model offset mortgages, where savings balances reduce the balance on which interest is charged, nor does it account for payment holidays if offered by 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.