Knowing your monthly mortgage payment is only half the picture. A proper mortgage repayment calculator shows you how that payment is split between interest and capital — and how that split shifts every year until the loan is cleared. This guide explains how to read that breakdown and use it to plan smarter.
Monthly Payment vs Amortisation: What’s the Difference?
Your monthly mortgage payment is fixed for the length of your deal (on a fixed-rate product). But the composition of that payment changes every month:
- Early years: most of the payment covers interest, because you owe the most capital
- Later years: most of the payment reduces the capital, because the outstanding balance has fallen
This month-by-month shift is called amortisation, and it’s why paying off a mortgage feels slow at first and faster toward the end.
Mortgage Payment Calculator
Estimate your monthly mortgage payment.
Illustrative estimate only. Actual payments may vary based on your mortgage, lender, fees, taxes and insurance.
Worked Example: £250,000 Mortgage Over 25 Years at 5%
| Year | Monthly Payment | Interest Portion | Capital Portion | Balance Remaining |
|---|---|---|---|---|
| 1 | £1,461 | £1,033 | £428 | £244,700 |
| 5 | £1,461 | £949 | £512 | £222,300 |
| 10 | £1,461 | £824 | £637 | £190,600 |
| 15 | £1,461 | £654 | £807 | £147,900 |
| 20 | £1,461 | £419 | £1,042 | £89,600 |
| 25 | £1,461 | £6 | £1,455 | £0 |
Figures are illustrative, rounded, and based on a standard repayment amortisation formula — your actual schedule will depend on your exact rate, fees, and any rate changes when your deal ends.
Repayment vs Interest-Only Mortgages
A repayment mortgage calculator (like the table above) assumes you’re paying down both interest and capital, so the loan reaches zero by the end of the term — this is what most UK lenders require for residential mortgages today.
An interest-only calculation looks different: the monthly payment only covers interest, stays roughly level throughout the term (assuming a fixed rate), and the full original loan amount is still owed at the end unless you have a separate repayment vehicle in place (savings, investments, or selling the property).
What Changes Your Repayment Mid-Term?
Your deal ending. Most UK mortgages are fixed for an initial 2, 3, or 5 years, then revert to the lender’s standard variable rate (SVR) — currently averaging around 6.49%, notably higher than most fixed deals. Set a reminder to remortgage before this happens.
Overpayments. Paying extra reduces the capital balance faster, which cuts both the interest charged and the time left on the mortgage.
A rate change on a tracker or variable deal. If you’re on a tracker mortgage, your payment moves directly with the Bank of England base rate (currently 3.75%, as of September 2026) plus the lender’s margin.
Frequently Asked Questions
What’s the difference between a mortgage calculator and a repayment calculator?
A general mortgage calculator usually just gives you the monthly figure. A repayment calculator goes further, showing the interest/capital split and, often, a full year-by-year amortisation schedule — useful for understanding how overpayments or a shorter term would affect the loan.
Why is most of my early payment interest, not capital?
Because interest is charged on the outstanding balance, and the balance is highest at the start of the mortgage. As the balance falls, less interest accrues each month, so more of your fixed payment goes toward capital.
Does a repayment calculator account for fees?
Most calculators, including this one, estimate the interest/capital split based on the loan amount, rate, and term. Product fees, valuation fees, and broker fees are typically separate and should be added to your total cost picture.
Will my repayment change every month?
On a standard fixed-rate repayment mortgage, no — the payment stays the same each month during the fixed period, only the interest/capital split shifts. On a tracker or variable-rate mortgage, the payment itself can change if the underlying rate moves.
Can I switch from interest-only to repayment part-way through?
In many cases yes, subject to lender approval and an affordability check — this is worth discussing directly with a mortgage adviser, as it affects your monthly payment going forward.
Next Steps
Use the Mortgage Repayment Calculator above to get your own year-by-year breakdown, then talk to us about how overpayments could shorten your term, or use our borrowing guide if you’re still deciding on loan size.
This article is for general information only and does not constitute personalised financial advice. Your home may be repossessed if you do not keep up repayments on a mortgage secured against it. Figures are illustrative estimates — always confirm exact costs with a qualified mortgage adviser.