Mortgage Calculator
About the Mortgage
This free mortgage calculator helps you estimate your monthly mortgage payments, total interest paid, and understand how a home loan amortises over its full term. Whether you are buying a first home, refinancing an existing mortgage, or comparing property financing options, knowing your likely monthly commitment before you apply is essential. The calculation uses the standard amortisation formula. Your lender charges interest on the outstanding balance each month, and your fixed monthly payment is split between paying that interest and reducing the principal. In the early years of a 30-year mortgage the vast majority of each payment goes to interest — often 70-80% — while only a small slice reduces what you actually owe. As the balance shrinks, the split flips and progressively more of each payment goes toward the principal. This is why mortgages feel "front-loaded" and why overpaying early can save you a great deal of money in total interest over the life of the loan. To use the calculator, enter the total amount you plan to borrow (the loan amount, excluding your deposit), your expected annual interest rate, and the loan term in years. The calculator instantly returns your monthly payment, the total you will repay, and the total interest paid. Play with the numbers — for example, reducing a 30-year mortgage to a 15-year term usually raises the monthly payment but can slash total interest by well over half. Mortgage rates vary by country, lender, credit score, and deposit size. In the UK rates are often fixed for 2-5 years then move to a variable or tracker rate; in the US 30-year and 15-year fixed-rate mortgages are standard. Because interest compounds monthly, even a difference of 0.5 percentage points can mean tens of thousands of pounds or dollars in interest over a 30-year term. Use this calculator to stress-test different rates and terms before you talk to a lender, and always check whether the quoted rate is fixed, variable, or an introductory teaser rate.
How to use this tool
- Enter the total loan amount you wish to borrow — the property price minus your deposit. For a £300,000 home with a 10% deposit, that would be £270,000.
- Enter your annual interest rate as a percentage. If your lender quotes 3.5%, enter 3.5. If they quote an APR that includes fees, you can use that figure to see the true cost.
- Enter the loan term in years — typically 25 or 30 years, though 15 and 20-year terms are common.
- Click the Calculate button to see your estimated monthly payment, the total amount you will repay over the term, and the total interest paid.
- Adjust the deposit or term to see how it changes your payment, then compare scenarios side by side before discussing options with a lender.
Common uses
- First-time buyers working out whether they can afford a property
- Existing homeowners comparing a 15-year vs 30-year refinance
- Buy-to-let investors stress-testing rental income against mortgage costs
- Anyone deciding whether to overpay or extend their mortgage term
Frequently asked questions
How is mortgage interest calculated?
Mortgage interest is calculated using an amortisation formula. Each monthly payment covers the interest accrued that month plus a portion of the principal. Early payments are mostly interest; later payments are mostly principal.
What is the difference between APR and interest rate?
The interest rate is the cost of borrowing the principal. APR (Annual Percentage Rate) includes the interest rate plus other fees (origination, discount points, closing costs), giving you the true cost of the loan.
How much deposit do I need for a mortgage?
Most lenders require a minimum 5-20% deposit. A larger deposit (20%+) typically gets you better interest rates and avoids private mortgage insurance (PMI) in some markets.
Should I choose a 15 or 30-year mortgage?
A 15-year mortgage has higher monthly payments but dramatically lower total interest. A 30-year mortgage has lower monthly payments but you pay significantly more interest over time. Use this calculator to compare the totals before deciding.
How does overpaying affect my mortgage?
Overpaying reduces the principal directly, which means less interest accrues each month. Even modest overpayments in the first years can shorten the term by years and save thousands in interest.
Can I use this for a remortgage or refinance?
Yes. Enter your outstanding balance, the new rate, and the remaining term to see how refinancing at a lower rate changes your monthly payment and total interest.