UK Mortgage Calculator
Estimate your monthly repayment and Stamp Duty Land Tax (SDLT) for a residential purchase in England or Northern Ireland.
| Year | Principal paid | Interest paid | Remaining balance |
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Mortgage Calculator UK: How to Work Out Your Monthly Repayments
Quick summary: A mortgage calculator UK tool estimates your monthly repayment by applying your loan amount, interest rate, and mortgage term to a standard amortization formula. As of early 2026, the Bank of England reports the average effective interest rate on newly drawn UK mortgages at around 4.10%, though advertised fixed rates from individual lenders vary by loan-to-value and term.
Buying a home is one of the biggest financial decisions most people make, and a mortgage calculator UK tool is the fastest way to see whether a property is actually affordable before you commit. Rather than guessing what a £250,000 loan at today’s rates will cost you each month, a UK mortgage calculator applies the same formula lenders use internally to give you a realistic repayment figure in seconds. This guide explains exactly how that formula works, walks through several worked examples at current UK rates, and covers the extra costs — like Stamp Duty Land Tax — that a basic repayment figure doesn’t include.
What a Mortgage Calculator UK Tool Actually Calculates
A UK mortgage calculator typically estimates one or more of the following:
- Your monthly repayment based on loan amount, interest rate, and term
- The total interest paid over the life of the mortgage
- How repayments change on a repayment (capital + interest) vs. an interest-only mortgage
- The impact of overpayments on your loan term and total interest
- Loan-to-value (LTV) ratio, based on your deposit and property price
Most calculators assume a repayment mortgage, where each monthly payment covers both interest and a portion of the capital, so the loan is fully paid off by the end of the term — as opposed to an interest-only mortgage, where monthly payments cover interest only and the capital is repaid separately (often via savings or an investment plan).
Current UK Mortgage Rate Context (2026)
Interest rates are the single biggest variable in any mortgage calculation, and they move regularly. According to Bank of England data reported via Trading Economics, the effective interest rate on newly drawn mortgages in the UK was around 4.09–4.10% in early 2026, while the average rate across the entire outstanding stock of UK mortgages sat closer to 3.95% (tradingeconomics.com, citing Bank of England data). Advertised fixed-rate deals from individual lenders can sit above or below this average depending on the loan-to-value band, product fees, and whether it’s a 2-year, 5-year, or longer fixed term — so always check a specific lender’s current offer rather than relying on a single national average.
The Mortgage Repayment Formula
A UK mortgage calculator for a standard repayment mortgage uses the amortizing loan formula:
M = P × [ r(1 + r)ⁿ ] / [ (1 + r)ⁿ − 1 ]
Where:
- M = monthly repayment
- P = principal (the loan amount, i.e., property price minus deposit)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of monthly payments (mortgage term in years × 12)
This formula spreads your repayments so that, in the early years, a larger portion goes toward interest, and in later years, a larger portion goes toward paying down the capital — which is why overpaying early in a mortgage term saves disproportionately more interest than overpaying near the end.
Worked Examples
Example 1: £250,000 mortgage, 4.1% interest, 25-year term
- P = £250,000
- Annual rate = 4.1% → monthly rate r = 0.041 ÷ 12 = 0.003417
- n = 25 × 12 = 300 months
Monthly repayment ≈ £1,336 Total repaid over 25 years ≈ £400,800 Total interest paid ≈ £150,800
Example 2: £180,000 mortgage, 4.5% interest, 30-year term
- P = £180,000
- Monthly rate r = 0.045 ÷ 12 = 0.00375
- n = 30 × 12 = 360 months
Monthly repayment ≈ £912 Total repaid over 30 years ≈ £328,320 Total interest paid ≈ £148,320
Example 3: Shortening the term to see the impact
Same £180,000 loan at 4.5%, but over 20 years instead of 30:
- n = 20 × 12 = 240 months
Monthly repayment ≈ £1,138 (about £226 more per month) Total interest paid ≈ £93,120 (over £55,000 less interest than the 30-year term)
This comparison shows the core trade-off every UK mortgage calculator reveals: a shorter term means higher monthly payments but substantially less interest paid overall.
Don’t Forget Stamp Duty Land Tax (SDLT)
A mortgage calculator UK tool typically shows your repayment costs, but not the upfront tax due when you buy. For residential property purchases in England and Northern Ireland from 1 April 2025 onward, the standard SDLT bands are:
| Portion of property price | SDLT rate |
|---|---|
| Up to £125,000 | 0% |
| £125,001 – £250,000 | 2% |
| £250,001 – £925,000 | 5% |
| £925,001 – £1,500,000 | 10% |
| Above £1,500,000 | 12% |
First-time buyers get extra relief: no SDLT on the first £300,000 of a property’s value, and a discounted rate on the portion between £300,000 and £500,000 — but this relief doesn’t apply at all if the property costs more than £500,000 (gov.uk; taxscape.deloitte.com summary of the April 2025 threshold changes). Scotland and Wales use their own separate land transaction taxes rather than SDLT.
SDLT worked example
A first-time buyer purchasing a £280,000 home pays:
- £0 on the first £300,000 → but the property is under £300,000, so SDLT = £0 under First-Time Buyers’ Relief
A non-first-time buyer purchasing the same £280,000 home pays:
- 0% on the first £125,000 = £0
- 2% on £125,001–£250,000 (£125,000) = £2,500
- 5% on £250,001–£280,000 (£30,000) = £1,500
- Total SDLT = £4,000
Repayment vs. Interest-Only: What Changes in the Calculation
- Repayment mortgage: monthly payment includes capital + interest; the amortization formula above applies; balance reaches £0 at the end of the term.
- Interest-only mortgage: monthly payment = P × r only (just the monthly interest on the full outstanding balance); the capital sum is still owed in full at the end of the term and must be repaid separately.
For the £250,000 example above at 4.1%, an interest-only monthly payment would be roughly £854 — noticeably lower than the £1,336 repayment figure, but with the full £250,000 still outstanding at the end of 25 years.
Common Mortgage Calculator Questions
Does a mortgage calculator include fees? Most basic UK mortgage calculators only estimate the interest-and-capital repayment. They typically don’t include arrangement fees, valuation fees, legal fees, or Stamp Duty Land Tax — you need to budget for these separately.
Why do two mortgage calculators give slightly different results for the same numbers? Small differences often come from rounding methods, whether the calculator compounds interest daily vs. monthly, or whether product fees are added to the loan amount before the calculation.
What’s a good loan-to-value (LTV) ratio? Generally, the lower your LTV (i.e., the bigger your deposit relative to property price), the better the interest rate a lender will offer, since a lower LTV represents lower risk to the lender.
How do overpayments affect my mortgage calculator result? Regular overpayments reduce your outstanding capital faster, which reduces the interest charged on future payments and can shorten your overall mortgage term — many UK lenders allow penalty-free overpayments up to 10% of the balance per year.
FAQs
As of early 2026, the average effective rate on newly drawn UK mortgages was around 4.1%, according to Bank of England data — but the best rate for you depends on your deposit size, credit profile, and chosen term.
Most UK lenders require a minimum deposit of 5–10% of the property price, though a larger deposit (20%+) typically unlocks meaningfully lower interest rates.
First-time buyers in England and Northern Ireland pay no SDLT on the first £300,000 of a property’s price, provided the total price doesn’t exceed £500,000.
A repayment mortgage pays off both interest and capital each month, so the loan is cleared by the end of the term; an interest-only mortgage only covers the interest, leaving the full capital still owed at the end.
No — a mortgage calculator gives an estimate based on the numbers you enter. Your actual offer depends on a lender’s affordability assessment, credit check, and specific product terms.
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Conclusion
A mortgage calculator UK tool turns the amortizing loan formula — principal, monthly interest rate, and term — into a repayment figure you can actually plan a budget around. With average newly drawn mortgage rates sitting near 4.1% in early 2026, running your own numbers through the formula above, and remembering to factor in Stamp Duty Land Tax and other upfront costs, will give you a far more realistic picture of affordability than the advertised interest rate alone.