Enter your mortgage details to see your monthly payment, the total interest you'll pay over the full term, and a year-by-year amortisation breakdown. Add a monthly overpayment to see how much time and interest you could save.
Your monthly mortgage payment is calculated from three inputs: the loan amount (principal), the annual interest rate, and the term in years. The formula used — called the annuity formula — ensures that equal payments made each month will exactly pay off the loan plus all interest by the final month.
Each payment covers two things: the interest charged on the outstanding balance that month, and a portion of the original loan. Early in the term, the balance is large — so most of your payment goes to interest. Over time, the balance falls and more of each payment goes to capital. The amortisation chart above makes this shift visible.
By the final payment, virtually all of it is capital and almost no interest remains. This is why paying extra in the early years of a mortgage has such an outsized effect — every £1 of overpayment reduces the balance on which future interest is calculated.
Monthly payments cover only the interest — the capital (original loan) is never touched during the term. This gives lower monthly payments, but the full loan amount is still owed at the end of the term and must be repaid in a lump sum.
Lenders typically require evidence of a credible repayment vehicle — such as an investment portfolio, endowment policy, or property sale proceeds — before approving an interest-only mortgage. They are more commonly used for buy-to-let properties, or for borrowers with a clear plan to repay the capital.
Any amount above your standard monthly payment goes directly to reducing your balance. Because interest is charged on the remaining balance each month, a lower balance means less interest accrues in future months — and more of future payments go to capital. The benefit compounds: small overpayments made consistently can shave years off a 25-year mortgage.
Important: most fixed-rate mortgages allow penalty-free overpayments of up to 10% of the outstanding balance per year. Exceeding this limit may trigger an Early Repayment Charge (ERC). Always check your mortgage terms before overpaying. ERCs typically disappear when the fixed term ends.
| Interest rate | Monthly payment | Total interest | Total repaid |
|---|---|---|---|
| 3.5% | £1,001 | £100,374 | £300,374 |
| 4.0% | £1,056 | £116,702 | £316,702 |
| 4.5% | £1,112 | £133,499 | £333,499 |
| 5.0% | £1,169 | £150,754 | £350,754 |
| 5.5% | £1,228 | £168,452 | £368,452 |
| 6.0% | £1,289 | £186,581 | £386,581 |
All figures rounded to nearest £1. Assumes no overpayments.
With a repayment mortgage, each monthly payment covers both the interest charged that month and a portion of the original loan — so the balance steadily falls to zero over the term. With an interest-only mortgage, monthly payments only cover the interest, meaning the balance never reduces. At the end of the term, the full original loan amount is still owed and must be repaid in a lump sum — usually from savings, investments, or sale of the property.
Interest is calculated as a percentage of your outstanding balance each month. When your mortgage is new, the balance is at its highest — so the interest charge is also at its highest. For example, on a £200,000 mortgage at 4.5%, the interest in month one is £750. Your standard monthly payment might be £1,111, meaning only £361 goes to capital. As the balance falls, the interest charge falls, and more of each payment goes to capital. This is the nature of amortisation — the chart in the calculator makes this shift easy to see.
Overpaying reduces your outstanding balance, which in turn reduces the interest charged on future months. The earlier you overpay, the greater the effect. On a £200,000 mortgage at 4.5% over 25 years, overpaying by just £100/month from the start would save over £17,000 in interest and cut almost 3 years from the term. Overpaying by £300/month would save around £40,000 and cut nearly 7 years. Enter the numbers into this calculator to see your specific savings. Most lenders allow 10% of the outstanding balance per year penalty-free — always check your terms.
An amortisation schedule (or amortisation table) shows how your mortgage balance reduces over time. For each year, it shows the opening balance, how much of your payments went to interest, how much reduced the capital balance, and the closing balance for that year. In the early years of a 25-year mortgage, the closing balance barely moves — most payments are going to interest. By the final years, nearly every payment goes to capital and the balance falls rapidly. The table view in this calculator shows the full year-by-year breakdown for your specific mortgage.
When a fixed-rate deal ends, you typically move onto your lender's Standard Variable Rate (SVR), which is usually 1–3% higher than competitive new fixed-rate deals available in the market. This can significantly increase monthly payments. Most borrowers remortgage before this happens — switching to a new fixed deal with the same lender (a "product transfer") or moving to a better rate with a new lender. You can use this calculator to model what different rates would mean for your remaining balance and term, which helps you compare remortgage offers.
Yes — enter your current outstanding balance (not the original loan amount), your current interest rate, and the number of years remaining on your term. The calculator will show your current monthly payment and the amortisation for the remaining term. This is useful when comparing remortgage options, planning overpayments, or modelling what a rate change might mean for your budget. For your exact outstanding balance, check your most recent mortgage statement or your lender's online portal.
You now have a clear picture of your monthly payments. The next step is confirming what you can actually borrow and finding the right mortgage product for your circumstances. A whole-of-market broker can search hundreds of lenders, compare rates you cannot access directly, and secure a Decision in Principle at no cost to you — and without affecting your credit score. Want to understand how mortgage repayments are calculated? Read our Mortgage Repayment guide.
Find an FCA-authorised broker ↗Always check your broker is registered on the FCA Financial Services Register before proceeding.
Mortgage repayment is usually one piece of a larger financial picture. These tools and guides help you see the full picture before you buy.
Monthly repayment figures are calculated using the standard mortgage annuity formula, which is the industry-standard method used by UK lenders.