Mortgage Rate Calculator
Our mortgage rate calculator shows your monthly repayment and total interest cost for any combination of mortgage amount, interest rate, and term. Use it to stress-test your budget at higher rates, compare the true cost of different rate levels, or understand exactly how sensitive your monthly payment is to rate changes.
Mortgage Rate Calculator
See how different interest rates affect your monthly mortgage payments.
How Interest Rate Changes Affect Repayments
Mortgage payments are highly sensitive to interest rate changes, particularly on large balances. On a £250,000 mortgage over 25 years, the monthly repayment at various rates is: 3.5% = £1,251; 4.0% = £1,319; 4.5% = £1,389; 5.0% = £1,462; 5.5% = £1,537; 6.0% = £1,611. Each 0.5% increase costs approximately £70 per month — meaning a 2% rate increase on this mortgage adds nearly £300 per month to the payment.
This sensitivity is why the FCA requires lenders to stress-test affordability at rates 3% higher than the initial product rate — ensuring that borrowers can still service the debt if rates increase significantly during or after the initial fixed period.
Fixed vs Variable Rate Risk
The choice between fixed and variable rates is fundamentally a bet on future interest rate movements. A fixed rate locks in your payment for certainty; a tracker or variable rate exposes you to both upside and downside rate movements. This calculator helps you model what your payment would be at various rate scenarios — including the SVR you would revert to at the end of any fixed period.
Frequently Asked Questions
The Bank of England Monetary Policy Committee sets the base rate eight times per year. Tracker mortgages are directly linked to it; fixed rates are priced relative to swap rates in the wholesale market. Check the current rate and historical trend at bankofengland.co.uk.
The best rate depends on your LTV, income, credit history, and whether you want a product fee. Comparison sites and whole-of-market mortgage advisers can identify deals that fit your profile. Our Compare Two Mortgages Calculator helps you evaluate any two specific deals side by side including fees.
The APRC is the overall cost of the mortgage expressed as a percentage, calculated over the full mortgage term. It includes the initial product rate, any fees, and the reversion rate (SVR). For comparing two mortgages over their full life, the APRC is more useful than the headline rate — though most borrowers remortgage before the SVR is relevant.
Longer terms do not typically attract higher interest rates — the rate is set by LTV, credit profile, and market conditions. What changes with the term is the monthly payment and total interest paid. A 30-year term has a lower monthly payment than a 25-year term at the same rate, but significantly higher total interest. Our Mortgage Overpayment Calculator shows the saving from shortening your effective term through overpayments.
Budget at your current rate plus 1.5–2%, to account for potential increases when you next remortgage. If your mortgage payment at the higher rate is affordable, you have a reasonable buffer. If it is not, consider whether a longer-term fix or a smaller mortgage would provide more security.
Enter your mortgage balance, current interest rate, and term. The calculator shows your current monthly payment and the impact of rate changes — either upward movements for stress-testing affordability or downward movements for planning overpayment. The payment change per 0.25% rate movement illustrates the interest rate sensitivity of your specific mortgage. Larger balances and longer terms are more sensitive to rate changes. This is particularly useful during periods of rate uncertainty: knowing that a 0.5% increase adds £X per month to your payment helps you assess whether your budget has sufficient headroom. Compare the results at your current fixed rate versus the estimated SVR you would revert to at the end of your deal.
Important Information
This calculator is provided for general information and planning purposes only. It does not constitute financial or tax advice and should not be relied upon as such. Figures are indicative estimates based on simplified, publicly available criteria and stated assumptions. Actual results depend on your full circumstances. See our Disclaimer for further information.