Rates & sources
Standard amortisation formulas used across UK lenders. Interest rates move daily — confirm with your lender or broker.
Source: Bank of England — Statistics — figures refreshed at the start of each tax year.
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.
A realistic New Zealand planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
APR (%)
5%
Compounding Periods Per Year
25 years
After entering these figures, focus on result first and then rerun the tool with a more cautious assumption to understand the realistic range of outcomes rather than relying on a single estimate.
How to read your results
Result
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 converts an Annual Percentage Rate (APR) to an Annual Percentage Yield (APY) using the standard compounding formula: APY = (1 + APR/n)^n − 1, where n is the number of compounding periods per year. Common compounding frequencies are daily (365), monthly (12), quarterly (4), and annually (1). When n equals 1, APR and APY are identical. The calculator can also work in reverse, deriving the equivalent APR from a known APY. In the UK, the regulatory equivalent of APY for savings products is the AER (Annual Equivalent Rate), governed by the Financial Conduct Authority. For mortgage and credit products, the relevant disclosure figure is the APRC, which incorporates fees alongside the interest rate. This tool performs the mathematical conversion only and does not incorporate fees or other charges.
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.
Frequently asked
Use arrow keys to navigate items, Enter or Space to expand/collapse.
End-of-article next steps
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