Mortgage repayment calculator
See your exact monthly payment, total interest, and how your balance falls over time. All in plain English — no jargon.
Your monthly payment looks manageable — but notice how much goes to interest in the early years. That’s completely normal. Every payment chips away at the balance, and each month slightly less goes to interest. This is why overpaying even a little early on saves a disproportionate amount over the full term.
What is LTV?
Loan-to-value is your mortgage as a percentage of the property price. Lower LTV unlocks better interest rates from lenders.
Why term length matters
A longer term means lower monthly payments — but you pay significantly more interest in total over the life of the mortgage.
Fixed vs variable
A fixed rate gives certainty for 2–5 years. A variable rate moves with the Bank of England base rate — lower risk when rates fall.
The power of overpaying
Even £50–100 extra per month can save thousands in interest and shave years off your mortgage. The earlier the better.
Please note: This calculator is for guidance and illustrative purposes only. Results are based on the figures you enter and assume a constant interest rate throughout the full mortgage term. Actual payments may vary. This is not financial advice — please speak to a qualified mortgage adviser or broker before making any decisions.
Calculator results are estimates based on the information you enter and the assumptions built into the tool. They are illustrative only and should not be relied upon as accurate projections. Rates, thresholds and rules change regularly; always verify figures with an appropriate professional or official source before acting on them.
What is a mortgage repayment calculator?
A mortgage repayment calculator works out your monthly payment based on three inputs: the loan amount (how much you are borrowing), the interest rate, and the mortgage term (how many years you are repaying over). It uses these three numbers to calculate the fixed monthly payment that will repay the loan in full by the end of the term.
Every mortgage repayment is split into two parts: interest (the cost of borrowing) and capital (reducing the outstanding balance). In the early years of a mortgage, the majority of each payment goes toward interest. As the balance falls, the split gradually shifts — more capital, less interest — until the final payment clears the remaining balance entirely. This calculator shows both the monthly payment and the total interest paid over the full term, so the true cost of the mortgage is visible rather than just the monthly figure.
How to use this calculator
Loan amount: Enter the amount you are borrowing, not the property price. If you are buying a £280,000 property with a £40,000 deposit, the loan amount is £240,000.
Interest rate: Enter the annual interest rate on your mortgage. For a fixed-rate mortgage, this is the rate on your offer document. The tracker will change as the Bank of England base rate changes. If you want to compare deals, run the calculator twice — once at your current rate and once at the alternative rate.
Mortgage term: Enter the number of years remaining on your mortgage. For a new mortgage, this is typically 25 or 30 years. For an existing mortgage where you are partway through, enter the years remaining, not the original term.
Reading the result: The calculator shows your monthly payment, the total amount repaid over the full term, and the total interest paid. The difference between the total repaid and the loan amount is the total interest cost – this number is often larger than people expect, particularly on longer terms.
What to look for in the results
Monthly payment: Check that this is affordable against your take-home pay. Most lenders recommend keeping mortgage payments below 35% of net monthly income, though affordability depends on your full financial position.
Total interest: The total interest figure shows the full cost of borrowing over the term. On a £200,000 mortgage at 5% over 25 years, the total interest is approximately £146,000, nearly three-quarters of the original loan amount. This figure reduces significantly with overpayments or a shorter term.
Rate comparison: Run the calculator at your current rate, then at the best available rate in the market. The monthly difference multiplied by 12 shows the annual savings from switching. Compare this to any early repayment charge to decide whether switching makes sense.
Frequently asked questions
What is the difference between a repayment mortgage and an interest-only mortgage? A repayment mortgage reduces your outstanding balance with each payment until the loan is fully repaid at the end of the term. An interest-only mortgage charges only the interest each month — the original loan balance remains unchanged and must be repaid separately at the end of the term. Almost all residential mortgages are repayment mortgages.
Why does my monthly payment seem high at the start and lower by the end? Your monthly payment is fixed throughout the term — what changes is the split between interest and principal in each payment. In year one, most of each payment is interest because the balance is high. By year 20, most is capital because the balance has reduced significantly. The payment stays the same; the composition changes.
What happens if interest rates change during my mortgage? For a fixed-rate mortgage, your payment stays the same until the fixed period ends, regardless of rate changes. For a tracker or SVR mortgage, your payment will change when the rate changes. Run the calculator at different rates to see how your payment would change at different rate scenarios.
How does overpaying affect the calculation? Overpayments reduce the outstanding balance more quickly, lowering the interest charged in subsequent months and allowing more of each future payment to go toward capital. Use the mortgage overpayment calculator alongside this one to see the specific effect of regular overpayments on your term and total interest.
Can I use this calculator for buy-to-let mortgages? Yes- the calculation is identical. Enter the loan amount, rate and term regardless of whether the property is residential or buy-to-let.
The information on this site is for educational and informational purposes only. Nothing on Be More Peter constitutes financial advice, and nothing should be treated as such. The calculators, articles and tools on this site are designed to help you understand financial concepts and run indicative numbers - they are not a substitute for professional advice tailored to your specific circumstances. Before making any financial decision - including decisions about mortgages, pensions, investments, savings or insurance — you should seek independent financial advice from a qualified adviser who is authorised and regulated by the Financial Conduct Authority (FCA). Calculator results are estimates based on the information you enter and the assumptions built into the tool. They are illustrative only and should not be relied upon as accurate projections. Rates, thresholds and rules change regularly - always verify figures with an appropriate professional or official source before acting on them. Be More Peter is not authorised or regulated by the FCA. The content on this site does not constitute a financial promotion.
Related tools and posts
- Mortgage overpayment calculator — see how extra payments reduce your term and total interest
- Remortgage calculator — compare your current rate against alternatives
- LTV calculator — check which rate tier your equity puts you in
- What is a repayment mortgage and how does it work?
- What happens when your fixed rate ends?