Mortgage Calculator - Work Out Your Monthly Repayments

Use the mortgage calculator

Type the property price, your deposit, the interest rate your lender is offering and the term in years into the tool above. It instantly returns your monthly mortgage payment, the total amount repaid and the total interest - so you can compare two deals side by side before you commit.

How a mortgage repayment is worked out

A standard UK residential mortgage is a repayment (capital and interest) loan. Every month you pay back a slice of the amount you borrowed plus the interest charged on the balance that is still outstanding. Early on, most of your payment is interest; as the balance shrinks, more of each payment chips away at the capital. That is why the loan barely moves in the first few years and then accelerates near the end.

The amount you actually borrow is the property price minus your deposit:

Loan amount = Property price − Deposit

The monthly payment then comes from the standard amortisation formula:

M = P × [ r × (1 + r)ⁿ ] ÷ [ (1 + r)ⁿ − 1 ]

• M = monthly payment
• P = loan amount (the capital you borrow)
• r = monthly interest rate = annual rate ÷ 12 (so 4.5% a year is 0.045 ÷ 12 = 0.00375)
• n = total number of monthly payments = term in years × 12 (25 years = 300 payments)

The three levers that move your payment are the size of the loan, the interest rate and the term. A bigger deposit shrinks P. A lower rate shrinks r. A longer term raises n, which cuts the monthly figure but increases the total interest, because you owe money for longer. Your loan-to-value ratio - the loan as a percentage of the property price - also decides which interest rates you qualify for: the more you put down, the cheaper the rate banks tend to offer.

Worked example: a first-time buyer couple

Priya and Tom are buying their first home for £280,000 with a £42,000 deposit (15%). They are offered a five-year fixed rate of 4.5% over a 25-year term.

Step 1 - the loan: £280,000 − £42,000 = £238,000 borrowed.

Step 2 - the inputs: r = 0.045 ÷ 12 = 0.00375, and n = 25 × 12 = 300 payments.

Step 3 - the formula: putting those into M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ − 1] gives a monthly payment of about £1,323.

Over the full 25 years they would pay roughly £1,323 × 300 = £396,800, of which about £158,800 is interest on top of the £238,000 they borrowed. Seeing the interest written out as a single number is sobering, but it is exactly why the rate and term matter so much.

How term and interest rate change the numbers

Keep the same £238,000 loan and watch what happens when you change one lever at a time.

Stretch the term to 30 years. The monthly payment falls to about £1,206 - roughly £117 a month cheaper. But you pay for an extra five years, so total interest climbs to around £196,100. That longer term costs about £37,000 more in interest for the breathing room of a lower monthly bill.

The rate rises by one percentage point (4.5% to 5.5%, 25-year term). The monthly payment jumps from about £1,323 to roughly £1,462 - about £139 a month more, or close to £1,700 a year. This is why locking a competitive rate, and overpaying when you can, makes such a difference. Our mortgage overpayment calculator shows how even £100 a month can knock years off the term.

Figures are rounded estimates to show the direction of travel; your lender's exact illustration may differ by a few pounds.

The costs this calculator does not include

Your monthly mortgage payment is only part of the picture. Before you decide what you can afford, budget for:

• Stamp duty. This is a different tax in each UK nation - SDLT in England and Northern Ireland, LBTT in Scotland and LTT in Wales - each with its own bands and rates. Check the bill with our stamp duty calculator before you fix your deposit.
• Buildings insurance, which most lenders require from completion day.
• Product and arrangement fees, often £500–£1,500, sometimes added to the loan (so you pay interest on them).
• Valuation, survey and conveyancing fees.
• Ground rent and service charges on leasehold flats.

To sense-check how much a lender might actually offer you, use the mortgage affordability calculator or the how much can I borrow calculator, which weigh your income and outgoings rather than just the property price.

Things to watch before you fix a deal

Repayment vs interest-only. This tool assumes a repayment mortgage, where you clear the whole balance by the end. On an interest-only mortgage your monthly cost is lower because you only pay the interest - but the full capital is still owed at the end and you need a credible plan to repay it. Most residential lenders only offer interest-only in limited cases; it is more common for buy-to-let.

The end of your fixed period. When a two- or five-year fix ends you usually roll onto the lender's standard variable rate (SVR), which is typically much higher. Diarise the expiry and shop around early - a remortgage often saves more than people expect. Compare new deals with the remortgage calculator.

Variable and tracker rates move. If your rate tracks the Bank of England base rate, your payment can rise or fall. Stress-test your budget against a rate one or two points higher than today's before you sign.

Common mistakes people make

• Forgetting the deposit reduces the loan, not the price. You pay interest on what you borrow, so a bigger deposit lowers both the monthly payment and the total interest. Plan it with a house deposit calculator.
• Chasing the lowest monthly payment by stretching the term. A 35-year term feels affordable but can add tens of thousands in interest. Look at the total cost, not just the monthly figure.
• Ignoring fees. A headline rate with a £1,499 fee can be dearer than a slightly higher rate with no fee - always compare the total cost over the fixed period.
• Assuming the rate is fixed forever. Most UK deals fix for two to five years, then revert to the SVR. The calculator shows the cost at one rate; reality is usually a sequence of rates.
• Overlooking overpayment limits. Many fixed deals cap penalty-free overpayments at 10% of the balance a year; go over and you may face an early repayment charge.

Where to get regulated advice

A mortgage is the biggest financial commitment most people make, so it is worth getting it right. The government-backed MoneyHelper guide to buying a home explains the process in plain English, and you can confirm any broker or lender is authorised on the FCA Financial Services Register. If your rate is variable, the Bank of England base rate is the figure that drives most changes.

These results are estimates for guidance only and not personal financial advice. Your lender's binding mortgage illustration is the figure to rely on, and a qualified mortgage adviser can recommend the right product for your circumstances.

Who should use this calculator

This is for the stage before you have a mortgage offer: you have found a price you like, you know roughly what deposit you can raise, and you want to know what the monthly payment would be. Because it starts from the property price and deposit rather than a loan amount, it also shows you the thing lenders actually care about — how much you are borrowing against the value of the house.

If you already know your loan amount, or you are modelling overpayments on a mortgage you hold today, the mortgage repayment calculator is the better starting point. If your question is how large a mortgage a lender would agree to at all, that is income-driven rather than price-driven, so use the borrowing calculator first and come back here with a realistic price.

What this calculator assumes

• A capital-and-interest repayment mortgage by default, where every payment clears some of the debt. Switching to interest-only shows a lower monthly figure, but the balance is still owed in full at the end of the term.
• The interest rate you enter applies for the whole term. Real UK mortgages are fixed for two to five years and then revert to a variable rate, so treat the total-interest figure as a comparison tool, not a prediction.
• Payments are monthly and start immediately, with interest compounding monthly.
• Overpayments — whether a regular extra amount or a one-off lump sum in a chosen year — reduce the capital, which is why they cut the term as well as the interest.

Limitations — what it does not cover

• Rate changes. Nothing here models the jump when a fixed period ends, which is usually the largest change to your payment you will experience.
• Fees. Arrangement, valuation, broker and early-repayment charges are excluded, and an early-repayment charge can wipe out the benefit of overpaying.
• Overpayment limits. Most fixed deals cap penalty-free overpayments at around 10% of the balance a year; this calculator does not enforce that cap.
• Whether a lender would approve it. Affordability is assessed on income, outgoings and a stressed interest rate, not on the payment shown here.
• The other costs of buying — stamp duty, conveyancing, survey, insurance and ground rent or service charges on a leasehold flat.

Related calculators

Plan the rest of your purchase with the mortgage repayment calculator, see what you could borrow with the mortgage affordability calculator, and check the tax on your purchase with the stamp duty calculator.

The numbers: what every £100,000 of mortgage costs

Monthly repayments per £100,000 borrowed, using the standard repayment formula lenders use. Multiply for your own loan size (a £250,000 mortgage = 2.5 times these figures).

The repayment formula behind the calculator:

Rates move with the Bank of England base rate; check the current base rate and free guidance from MoneyHelper (the government-backed money service).