Calculate your exact monthly mortgage payment, total interest cost, and full year-by-year amortisation schedule. Includes overpayment calculator.
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Our mortgage calculator uses the standard amortisation formula used by all UK lenders. Enter your property price, deposit, interest rate, and term — the calculator instantly shows your monthly payment, total interest, and a full year-by-year breakdown of how your balance reduces over time.
The monthly payment formula is: 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 monthly payments. This is the standard calculation method used by all UK banks and building societies.
The calculator supports both mortgage types. On a repayment mortgage (the standard choice for most homebuyers), each monthly payment covers both the interest charge and a portion of the outstanding capital. By the end of the term, the balance is zero and you own the property outright.
On an interest-only mortgage, your monthly payment covers only the interest — the loan balance never reduces. At the end of the term, you still owe the original loan and must repay it in full, typically by selling the property, using savings, or investing in a separate repayment vehicle. Interest-only is common in buy-to-let mortgages but rarely recommended for residential buyers without a robust repayment strategy.
Even modest monthly overpayments can dramatically reduce the total cost of your mortgage. The reason is mathematical: reducing the outstanding balance early reduces all future interest calculations, creating a compound saving effect. On a £270,000 mortgage at 4.84% over 25 years, overpaying just £200/month:
Most UK fixed rate mortgages allow overpayments of up to 10% of the outstanding balance per year without Early Repayment Charges. Always check your specific mortgage terms before overpaying.
The deposit you enter in the calculator determines your Loan-to-Value (LTV) ratio — and this directly affects the interest rate available to you. UK mortgage rates are organised into LTV bands: crossing from 90% to 85% LTV, or from 80% to 75% LTV, typically unlocks meaningfully better rates and reduces your monthly payment.
If you're close to an LTV threshold, it may be worth saving a little longer to cross into the next band. Use the calculator to compare your monthly payment and total interest at different deposit levels — the difference is often significant over a 25-year term.