Mortgage Repayment Calculator
Calculate your monthly mortgage repayments, total interest cost, and see a full year-by-year amortisation schedule. Add overpayments to see how much interest and time you could save.
Enter your mortgage details
Your monthly payment, total interest, and a full repayment schedule will appear here.
How mortgage repayment calculations work
A repayment mortgage works by making equal monthly payments over the agreed term. Each payment covers the interest accrued that month plus a portion of the outstanding capital. Because the balance reduces with every payment, the interest element shrinks over time, meaning an ever-larger share of each payment goes towards paying off the loan. By the final payment, the entire outstanding balance has been cleared.
Overpayments directly reduce the outstanding balance — so every extra pound you pay in stops accruing interest immediately. This compounds over the remaining term, often saving many times the overpayment in interest. Most lenders allow overpayments of up to 10% of the outstanding balance per year without early repayment charges. Check your mortgage terms before making large one-off payments.
Frequently asked questions
- How is a monthly mortgage repayment calculated?
- For a repayment mortgage, the monthly payment is calculated using the standard annuity formula: M = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of months. This ensures the loan is fully repaid at the end of the term with equal payments throughout.
- What is an amortisation schedule?
- An amortisation schedule shows how each mortgage payment is split between repaying the outstanding capital (principal) and paying the interest charge. Early in the mortgage, most of each payment goes towards interest. Over time, as the outstanding balance falls, a growing proportion goes to capital. The schedule lets you see your exact balance at any point in the term.
- How much can overpayments save on a UK mortgage?
- Overpayments reduce your outstanding balance, which means less interest accrues each month. On a £200,000 mortgage at 5% over 25 years, a £200/month overpayment typically saves around £25,000–£30,000 in total interest and cuts the term by 5–7 years — though the exact saving depends on when the overpayment starts and whether your lender applies any early repayment charges (ERCs). This calculator shows the saving for your specific inputs.
- What is the difference between a repayment and interest-only mortgage?
- With a repayment mortgage your monthly payment covers both the interest due and a capital repayment, so the balance falls each month and the mortgage is fully paid off at the end of the term. With an interest-only mortgage you only pay the monthly interest — the full capital remains outstanding at the end and must be repaid as a lump sum (usually from savings, investments or sale of the property). Most residential mortgages in the UK are repayment.
- Are there early repayment charges on overpayments?
- Most fixed-rate mortgages allow overpayments of up to 10% of the outstanding balance per year without incurring an early repayment charge (ERC). Overpaying more than the allowed amount during a fixed-rate period can trigger an ERC, typically 1–5% of the overpaid amount. Always check your mortgage terms before making large overpayments.