Mortgage Repayment Calculator
HotWork out your monthly mortgage payments and total interest over your term.
How it works
A repayment mortgage pays down two things every month: the interest charged on your outstanding balance, and a portion of the original loan (the capital). Early in the term, most of each payment goes towards interest because the balance is still high; as the balance shrinks, more of each payment goes towards capital instead — which is why the balance falls slowly at first and much faster near the end of the term, even though your monthly payment stays the same on a fixed rate.
An interest-only mortgage works differently: your monthly payment only covers the interest, so the original loan amount doesn't reduce at all during the term. That makes monthly payments lower, but you need a separate repayment plan — savings, investments, or selling the property — to clear the full loan when the term ends.
UK context
UK mortgages are typically quoted as fixed, tracker or standard variable rate (SVR) — the rate type affects whether your payment stays the same or moves during the deal, not how the repayment/interest-only maths itself works. See our guide to UK mortgage rate types for the difference. Terms of 25 years are the traditional UK default, though 30–35 year terms have become more common as a way to reduce monthly payments (at the cost of more total interest paid).
If you're buying rather than remortgaging, remember Stamp Duty Land Tax (SDLT) is a separate cost on top of the mortgage itself, with its own thresholds and rates set by the government.
Tips
- Overpaying — even by a small amount each month — reduces the balance faster and cuts total interest significantly over a 25-year term, though most lenders cap penalty-free overpayments at around 10% of the balance per year.
- Check for an Early Repayment Charge (ERC) before overpaying beyond your lender's allowance or remortgaging during a fixed deal — these charges can be substantial.
- A slightly lower rate can be outweighed by a higher arrangement fee on a short-term deal — always compare the total cost over the deal period, not just the headline rate.
Frequently asked questions
How is a mortgage monthly payment actually calculated?
Repayment mortgages use an amortisation formula based on the loan amount, monthly interest rate and number of payments, structured so the loan is fully paid off (principal and interest) by the end of the term. Our calculator does this maths for you and shows the split between interest and capital.
What's the difference between the interest rate and APRC?
The interest rate is what's applied to your outstanding balance. The APRC (Annual Percentage Rate of Charge) includes the interest rate plus most mandatory fees, expressed as a yearly rate — it's the better figure for comparing the true cost of different mortgage offers.
Does a longer mortgage term always cost more overall?
Usually yes — a longer term lowers your monthly payment but means you pay interest for longer, so the total interest paid over the life of the loan is typically higher, even at the same interest rate.
Can I switch from interest-only to repayment part-way through?
Many lenders allow this, sometimes with conditions, since it changes your risk profile in their eyes. Speak to your lender or a mortgage broker — switching earlier in the term gives more time to benefit from the extra capital repayment.
A quick note
Figures and thresholds referenced above (tax bands, VAT rates, redundancy caps and similar) are set by the government and reviewed periodically — this page explains how the calculation works, not necessarily today's exact numbers. Always check the official sources below before making a financial decision, and see our full disclaimer.