Mortgage Calculator
Our free mortgage calculator shows your monthly repayment, total interest, and total cost for any mortgage amount, interest rate, and term. Whether you are buying your first home, remortgaging to a new deal, or stress-testing your affordability at higher rates, this calculator gives you the numbers you need in seconds.
Mortgage Repayment Calculator
Calculate your monthly mortgage repayments based on loan amount, rate and term.
How Monthly Mortgage Repayments Are Calculated
A repayment mortgage uses a standard annuity formula. Your monthly payment is calculated so that equal monthly instalments repay both the interest that accrues each month and a portion of the capital, so that the full balance is cleared exactly at the end of the term. In the early years, the vast majority of each payment covers interest. As the balance falls, more of each payment goes toward capital repayment.
On a £200,000 mortgage at 4.5% for 25 years, the monthly payment is £1,111. Over 300 months, total repayments are £333,300 — of which £133,300 is interest. Reducing the term to 20 years raises the monthly payment to £1,265 but cuts total interest to £103,600 — a saving of nearly £30,000 in interest at the cost of £154 more per month.
Interest-Only vs Repayment
An interest-only mortgage charges only the monthly interest, leaving the full capital outstanding at the end of the term. On the same £200,000 at 4.5%, the interest-only payment is just £750 per month — but you still owe £200,000 at the end of 25 years. Interest-only mortgages require a credible repayment vehicle (typically an investment portfolio or property sale) and are far harder to obtain from mainstream lenders than they were pre-2008.
The Impact of Rate Changes
On a tracker or variable mortgage, even small rate changes significantly affect monthly payments. A 0.5% rate increase on £200,000 over 25 years raises the monthly payment by approximately £52. A 1% increase raises it by £104. Building a buffer of 1–2% above your current rate when stress-testing your budget is a prudent approach recommended by most mortgage advisers.
Frequently Asked Questions
Most lenders cap mortgage lending at 4 to 4.5 times your annual gross income, subject to affordability checks. Joint applications use combined income. Other factors including existing debt, childcare costs, and credit history affect the final amount. Our Mortgage Affordability Calculator gives you a detailed estimate based on your income and outgoings.
A fixed-rate mortgage locks your interest rate (and therefore your monthly payment) for a set period — typically two or five years. A tracker or variable rate mortgage moves with the Bank of England base rate or lender’s standard variable rate. Fixed rates offer certainty; variable rates may be lower initially but carry rate risk.
A longer term reduces monthly payments but dramatically increases total interest paid. A 30-year mortgage on £200,000 at 4.5% costs £163,700 in interest — £60,000 more than a 20-year term. Overpaying by even a small amount each month can significantly reduce the effective term and total interest.
An offset mortgage links your savings to your mortgage. Rather than earning interest on your savings, the balance reduces the mortgage amount on which interest is charged. If you have £20,000 in savings linked to a £200,000 mortgage, you only pay interest on £180,000. Our Mortgage Offset Calculator shows the interest saving for any savings level.
Yes. Our Mortgage Overpayment Calculator shows exactly how much interest you save and how many months you cut from your mortgage term by making regular or one-off overpayments.
Enter the loan amount (property price minus deposit), the annual interest rate, and the term in years. The calculation uses the standard amortisation formula: monthly payment equals principal times the monthly rate, divided by one minus the monthly rate to the power of negative total months. This is the formula all UK lenders use. A longer term reduces monthly payments but increases total interest significantly — compare the total interest paid at 25 versus 30 years to see the cost of the extended term. The overpayment field shows how much term and interest is saved by paying extra each month. Most lenders allow 10% of the balance per year without early repayment charges — check your specific terms.
Important Information
This calculator is provided for general information and planning purposes only. It does not constitute financial or tax advice and should not be relied upon as such. Figures are indicative estimates based on simplified, publicly available criteria and stated assumptions. Actual results depend on your full circumstances. See our Disclaimer for further information.