How is the UK mortgage monthly repayment calculated?

For a repayment mortgage, this tool uses the standard amortization formula: M = P [ i(1+i)^n ] / [ (1+i)^n - 1 ], where P is the loan amount (property price minus deposit), i is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments (term in years multiplied by 12). This assumes a fixed rate for the full term.

What is the difference between repayment and interest-only?

A repayment mortgage pays down both interest and part of the loan balance each month, so the balance reaches zero at the end of the term. An interest-only mortgage pays just the interest each month, so the monthly cost is lower, but the full loan amount is still owed at the end of the term and must be repaid separately, for example from savings or the sale of the property.

Does this calculator include stamp duty land tax?

No. This tool calculates the mortgage repayment on the loan amount only. Stamp Duty Land Tax (SDLT) is a separate one-off cost paid on completion and depends on the property price, whether you are a first-time buyer, and whether you already own another property.

What mortgage term and rate should I use?

UK mortgage terms commonly range from 5 to 35 years, with 25 years being typical. Interest rates vary by lender, deposit size, and whether the deal is fixed or variable, so use the rate quoted on your specific mortgage offer or a current representative rate from a lender comparison site for the most accurate estimate.

Why does a larger deposit lower my monthly repayment?

A larger deposit reduces the loan amount you need to borrow, which directly lowers both the monthly repayment and the total interest charged over the term. A bigger deposit can also move you into a lower loan-to-value band, which often qualifies you for a lower interest rate as well.

UK Mortgage Calculator

Name: UK Mortgage Calculator
Availability: InStock
Author: Nham Vu

Enter your property price, deposit, interest rate, and mortgage term to see your monthly repayment, total interest, and a year-by-year repayment schedule.

Mortgage Details

Property Price

Deposit 20.0%

Mortgage Term

Annual Interest Rate

Repayment Type

Repayment Interest-only

Monthly Repayment

Live calculation

Monthly Repayment

£0.00

Loan Amount

£0

Total Interest

£0

Total Repaid

£0

Payoff Date

—

Year	Annual Payment	Interest Paid	Principal Paid	Balance

Summary

Enter your property price, deposit, interest rate, and mortgage term to see your monthly repayment, total interest, and a year-by-year repayment schedule.

How it works

Enter the property price and your deposit amount; the deposit percentage updates automatically.
Choose your mortgage term in years and enter the annual interest rate.
Select Repayment (capital and interest) or Interest-only.
Read the monthly repayment, total interest, and total repaid figures as you type.
Expand the repayment schedule for a year-by-year breakdown of interest, principal, and remaining balance.

Use cases

A first-time buyer comparing monthly repayments on a 25-year term versus a 30-year term at the same rate.
Someone remortgaging who wants to see how a higher deposit lowers the loan amount and monthly cost.
A buy-to-let landlord comparing repayment versus interest-only monthly costs on the same loan.
Anyone checking how much total interest builds up over the full mortgage term before applying.
A buyer testing how a small change in interest rate affects the monthly repayment.

Frequently Asked Questions

Last updated: 2026-07-21 · Reviewed by Nham Vu