UK Mortgage Calculator
Work out your monthly UK mortgage payment, total interest and loan-to-value — plus a Stamp Duty (SDLT) estimate with first-time buyer relief.
Estimated Monthly Payment
How It Works
A UK repayment mortgage is paid off in equal monthly instalments that cover both the interest and part of the capital. The monthly payment comes from the standard amortization formula, M = P × r(1+r)n / ((1+r)n − 1), where P is the loan amount (property price minus deposit), r is the monthly interest rate (annual rate divided by 12), and n is the number of monthly payments (years times 12). The payment stays the same every month, but the split changes over time: early payments are mostly interest, while later payments are mostly capital. If the interest rate is 0%, the payment is simply the loan divided by the number of months.
Loan-to-value (LTV) is the loan as a percentage of the property price: loan ÷ price × 100. A £270,000 loan on a £300,000 home is 90% LTV. Lenders use LTV to judge risk, and a lower LTV usually means access to cheaper mortgage deals, so a bigger deposit can pay off twice — a smaller loan and a better rate.
Stamp Duty Land Tax (SDLT) is a one-off tax paid when you buy a property in England or Northern Ireland. It is charged in bands, so each rate applies only to the part of the price inside that band — not to the whole price. The standard main-home rates from 1 April 2025 are:
| Portion of property price | SDLT rate |
|---|---|
| Up to £125,000 | 0% |
| £125,001 to £250,000 | 2% |
| £250,001 to £925,000 | 5% |
| £925,001 to £1,500,000 | 10% |
| Over £1,500,000 | 12% |
First-time buyer relief applies only if you have never owned a home before and the property costs £500,000 or less: you pay 0% on the first £300,000 and 5% on the part from £300,001 to £500,000. If the price is over £500,000, the relief is lost entirely and standard rates apply to the whole price — so a first-time buyer pays £10,000 on a £500,000 home but £15,000.05 on a £500,001 home.
Worked example: a £300,000 property with a 10% deposit (£30,000) leaves a £270,000 loan at 90% LTV. At 5.0% interest over 25 years (300 monthly payments), the monthly payment is £1,578.39. Over the full term you would pay £473,517.93 in total, of which £203,517.93 is interest. Stamp duty on the £300,000 price is £5,000 at standard rates (2% on £125,000 = £2,500, plus 5% on £50,000 = £2,500) — or £0 for a first-time buyer, since the price is within the £300,000 relief threshold.
How to Use This Calculator
Start with the property price, then enter your deposit. The pound and percentage fields stay in sync, so you can type either the amount you have saved or the percentage you want to put down — changing one updates the other. A 10% deposit on a £300,000 home is £30,000, leaving a £270,000 loan. Next, enter the annual interest rate and the loan term in years; the defaults are 5.0% and 25 years, but you should replace the rate with the one your lender quotes you, since your own rate depends on your credit history, the loan-to-value and current market conditions.
Finally, tick the first-time buyer box if you have never owned a home before — it applies stamp duty relief where it is available, and the results note whether relief was applied or lost. Results update as you type: the headline figure is your monthly payment, and the table shows the loan amount, loan-to-value, total interest, total amount paid and the stamp duty estimate. Try changing one thing at a time — a bigger deposit, a shorter term, a lower rate — to see how each choice moves the monthly payment.
Tips and Practical Advice
The deposit is the most powerful lever you have. A bigger deposit shrinks the loan, lowers the monthly payment and brings your loan-to-value down, which usually opens up cheaper mortgage deals. Test the deposit both ways: moving from 5% to 10% on a £300,000 home takes £15,000 more upfront, but it cuts the loan by £15,000 and the monthly payment by about £88 at 5.0% over 25 years.
Watch the stamp duty cliff at £500,000. First-time buyer relief disappears completely above that price, so a first-time buyer pays £10,000 on a £500,000 home but £15,000.05 on a £500,001 home — one pound more on the price costs £5,000.05 more in tax. If you are buying close to the threshold, it is worth knowing exactly where you stand before you offer.
Remember that stamp duty is a one-off cost paid when you buy, on top of your deposit — budget for it separately rather than folding it into the mortgage. And treat every figure here as an estimate for planning: your lender's quote will reflect your exact rate, credit history and fees, so confirm the final numbers with them before you commit.
Frequently Asked Questions
How is a UK monthly mortgage payment calculated?
With the standard amortization formula: monthly payment = loan x r(1+r)^n / ((1+r)^n - 1), where r is the monthly interest rate (annual rate / 12) and n is the number of monthly payments. For example, a £270,000 loan at 5.0% over 25 years (300 payments) costs £1,578.39 a month. The payment stays the same each month, but the split changes: early payments are mostly interest, later ones mostly capital.
How much stamp duty do first-time buyers pay?
First-time buyers in England and Northern Ireland pay no Stamp Duty on the first £300,000 of a home costing £500,000 or less, and 5% on the part between £300,001 and £500,000. So a first-time buyer pays £0 on a £300,000 home and £5,000 on a £400,000 home. Above £500,000 the relief is lost entirely and standard rates apply to the whole price.
Does this calculator work for Scotland and Wales?
The mortgage payment part works anywhere in the UK, but the stamp duty estimate is for England and Northern Ireland only. Scotland charges Land and Buildings Transaction Tax (LBTT) and Wales charges Land Transaction Tax (LTT), and both have different rates and thresholds, so the SDLT figure on this page does not apply there.
What is loan-to-value (LTV) and why does it matter?
Loan-to-value is the mortgage as a percentage of the property price: loan / price x 100. A £270,000 loan on a £300,000 home is 90% LTV. A lower LTV usually means access to cheaper mortgage deals and a smaller monthly payment, because the lender is taking less risk — a bigger deposit is the simplest way to bring LTV down.
What does the monthly payment include?
Only the capital-and-interest repayment on the mortgage. It does not include buildings insurance, life insurance, service charges or ground rent, so your real monthly housing cost will be higher. The stamp duty figure is also separate — it is a one-off tax paid when you buy, not part of the monthly payment.
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