Mortgage Calculator
Calculate your monthly mortgage repayment, total interest paid, and full amortisation schedule.
What this calculator does
This mortgage calculator works out what a UK mortgage costs each month and across its full term. Enter the property price, your deposit, the interest rate you have been quoted, and the term, and it returns the monthly repayment, the total interest paid over the life of the mortgage, and a complete amortisation schedule showing how each repayment splits between interest and capital.
The amortisation schedule is the part worth studying. A single monthly figure tells you whether the repayment is affordable; the schedule tells you what you are actually committing to — how long you spend paying mostly interest, when the balance starts falling meaningfully, and what the mortgage costs in total rather than per month.
When to use it
Most people reach for a mortgage calculator at three moments. Before viewing properties, to work backwards from a repayment you are comfortable with to a realistic price range. While comparing deals, to turn competing rate and fee combinations into monthly and lifetime figures you can rank against each other. And ahead of a remortgage, to see whether switching justifies the fees involved.
It is just as useful for the deal-expiry question that catches many UK borrowers out. Running your current fixed rate against your lender's standard variable rate shows the size of the payment jump waiting at the end of your deal period, which is the number that should drive when you start shopping for the next one.
Understanding the inputs
Property price and deposit together determine the amount borrowed, which is what interest is charged on. Your deposit also sets your loan-to-value ratio, and because lenders price in LTV bands, it is worth testing deposit figures either side of the 90, 85, 80, and 75 percent boundaries.
Enter the annual interest rate as quoted — the calculator converts it to a monthly rate internally. If you are on a fixed deal, remember the rate applies only for the deal period, so it is worth running the standard variable rate separately. Term is the repayment period in years, commonly 25 to 35 in the UK. The extra monthly payment field applies overpayments to the balance, which is the fastest lever for cutting total interest.
How is this calculated?
M = P[r(1+r)^n]/[(1+r)^n-1] where P is the principal loan amount, r is the monthly interest rate, and n is the number of payments.
A worked example
Take a £350,000 property with a 10 percent deposit of £35,000, leaving a £315,000 mortgage at 5.25 percent over 25 years. The monthly repayment works out at roughly £1,888, and total interest across the term comes to about £251,000.
In month one, close to £1,378 of that repayment is interest and only around £510 reduces the balance. Shortening the term to 20 years raises the repayment to roughly £2,120 but cuts total interest to about £194,000 — around £232 more per month to save roughly £57,000. Overpaying by £200 a month on the original 25-year term would clear it several years early and save a comparable sum.
Limitations and assumptions
This calculator models a repayment mortgage at a fixed rate. It does not include stamp duty, legal fees, survey costs, product or arrangement fees, buildings insurance, or any early repayment charge, and it assumes the rate holds for the entire term. Since most UK deals fix for two to five years, figures beyond your deal period are indicative only.
Interest-only mortgages, offset arrangements, and lenders that calculate interest daily rather than monthly will all produce slightly different results. For a binding figure, rely on the illustration your lender provides. Use this calculator for what it does well: comparing scenarios quickly and understanding the shape of the mortgage.
Common Questions
- How is a mortgage repayment calculated?
- Your monthly repayment comes from three numbers: the amount you borrow, the interest rate, and the term. The amortisation formula spreads them into a level monthly figure. Each repayment covers the interest accrued that month first, and the remainder reduces the outstanding balance.
- Does this include the other costs of buying?
- No. This is the mortgage repayment only. Stamp duty, solicitor and conveyancing fees, survey costs, buildings insurance, and any product or arrangement fee sit outside it. On a typical purchase those can add several thousand pounds up front, so treat this as one line in a larger budget.
- What happens when my fixed-rate deal ends?
- Most UK fixed rates run for two, three, or five years, not the full term. When the deal ends you move onto your lender's standard variable rate, which is usually markedly higher. Run your current rate and a realistic SVR figure through the calculator to see the jump before it arrives, and start looking at remortgage options around six months ahead.
- How much does the interest rate actually matter?
- More than most buyers expect. On a £300,000 mortgage over 25 years, one percentage point changes the monthly repayment by roughly £170 and the total interest by around £51,000. Comparing deals across a broker and a few lenders is one of the highest-value hours in the whole process.
- How does loan-to-value affect the rate I am offered?
- LTV is the mortgage as a percentage of the property value, and lenders price in bands — typically 60, 75, 80, 85, 90, and 95 percent. Dropping below a band boundary can secure a noticeably better rate, so if you are close to one, a slightly larger deposit can pay for itself many times over.
- What is the difference between repayment and interest-only?
- A repayment mortgage clears the balance by the end of the term. Interest-only covers just the interest, leaving the full amount outstanding at the end, to be settled by a separate repayment vehicle. Monthly costs are lower but total cost is higher and you build no equity through payments. This calculator models repayment mortgages.
- Should I overpay my mortgage?
- Overpaying reduces the balance immediately, removing all future interest that balance would have generated. Most fixed deals permit overpayments of up to 10 percent of the outstanding balance each year without penalty — beyond that, early repayment charges usually apply. Check your terms, then use the extra payment field to see the effect.
- Why does so little of my early repayment reduce the balance?
- Interest is charged on the amount outstanding, which is largest at the start. In the early years most of each repayment goes to interest and only a small portion reduces the balance. The ratio shifts steadily as the balance falls — the amortisation schedule above shows exactly when the crossover happens.
- What mortgage term should I choose?
- Twenty-five years has long been the UK default, though thirty and thirty-five year terms are increasingly common as a way to make monthly figures manageable. A longer term lowers the repayment and raises the total interest considerably. Many lenders allow you to shorten the term later at remortgage, which is often the more flexible route.
- How accurate is this estimate?
- The repayment figure is mathematically exact for a fixed-rate repayment mortgage. What it excludes are product fees, insurance, and any rate change after your deal period ends. Treat it as a reliable way to compare scenarios rather than a formal quotation — your lender's illustration is the binding document.
Related calculators
- Mortgage Payoff CalculatorSee how overpayments can reduce your mortgage term and save thousands in interest.
- Fortnightly Mortgage Payment CalculatorSee how making fortnightly mortgage payments instead of monthly can reduce your term and save interest.
- Mortgage Comparison CalculatorCompare two mortgage deals side by side to find which offers the lowest total cost over your term.