Key takeaway: A mortgage amortisation schedule shows you exactly how each monthly payment is split between interest charges and principal repayment over your entire mortgage term. In the early years, most of your payment covers interest, but as the balance falls, an increasing share reduces the principal. An amortisation schedule calculator lets you see this breakdown month by month and model how overpayments can shorten your term and cut total interest costs.

What Is a Mortgage Amortisation Schedule?

An amortisation schedule is a complete table showing every repayment you will make over the life of your mortgage, broken down into the interest portion and the principal (capital) portion. Although your monthly payment typically stays the same on a repayment mortgage, the split between interest and principal changes with each payment.

According to MoneyHelper, understanding how your repayments work helps you plan ahead and make informed decisions about overpayments (MoneyHelper, 2026). The concept of amortisation is covered in foundational finance texts such as Principles of Finance, which explain that the interest component declines over time as the outstanding balance falls.

In the UK, most residential mortgages are repayment mortgages (also called capital-and-interest mortgages), meaning each monthly payment reduces both the interest owed and the loan balance. Interest-only mortgages exist but are less common and do not amortise the principal during the term.

Why the Breakdown Matters for UK Mortgage Holders

Interest-Heavy Early Years

When you start a mortgage, the outstanding balance is at its highest, so the interest charged each month is also highest. A large share of your early payments goes to interest, with only a small amount reducing the principal. As the balance shrinks, the interest portion falls and the principal portion rises.

For example, on a £200,000 mortgage at 4 per cent over 25 years, your first monthly payment of roughly £1,055 might include around £667 in interest and only £388 toward the principal. By year 15, the same £1,055 payment could split closer to £400 interest and £655 principal.

Deal Periods and Reversion Rates

UK mortgages typically have an initial deal period (commonly two, three, or five years) at a fixed, tracker, or discount rate, after which the rate reverts to the lender’s standard variable rate (SVR). The SVR is almost always higher, so your monthly payment and the interest portion both jump when the deal ends.

An amortisation schedule lets you model what happens at reversion. You can see how much principal you will have paid down by the end of the deal, what your remaining balance will be, and how the new SVR payment splits between interest and principal. This visibility helps you decide when to remortgage to a new deal before reversion.

Overpayments and Early Repayment Charges

Many UK mortgage products allow you to overpay up to a certain limit each year (commonly 10 per cent of the outstanding balance) without incurring an early repayment charge (ERC). Overpayments reduce the principal directly, which cuts the total interest you pay and can shorten the mortgage term.

Read also: UK Mortgage Amortisation Schedule: See What Each Repayment Covers

An amortisation schedule calculator shows you the impact of regular or lump-sum overpayments: how much sooner the mortgage will be paid off and how much interest you save over the life of the loan. You can also model staying within your annual overpayment allowance to avoid ERCs.

What the Amortisation Schedule Calculator Shows You

The calculator generates a month-by-month table for your mortgage, displaying:

  • The payment number and date
  • Your monthly payment amount
  • The interest portion of that payment
  • The principal portion of that payment
  • The remaining balance after each payment
  • Cumulative totals for interest paid and principal paid

You can adjust the mortgage amount, interest rate, term, and add overpayments to see how the schedule changes. The calculator helps you answer questions such as:

  • How much of my payment actually reduces the loan balance each month?
  • How much total interest will I pay over the full term?
  • If I overpay £200 per month, how many years will I save?
  • What will my balance be at the end of my two-year fixed deal?

Important Information

This information is general educational guidance on how mortgage amortisation works in the UK. It is not regulated mortgage advice, and it is not personalised financial, lending, or legal advice. Refisage is not authorised by the Financial Conduct Authority (FCA).

Your home may be repossessed if you do not keep up repayments on your mortgage.

Interest rates, mortgage products, fees, and overpayment allowances vary by lender and your personal circumstances. Early repayment charges apply if you exceed your overpayment limit during a deal period. Always confirm current terms with an FCA-authorised mortgage adviser or lender before making decisions about overpayments or remortgaging. For guidance on mortgage options and repayments, visit MoneyHelper or speak to an FCA-authorised mortgage adviser.