Mortgage Calculator UK

What this UK mortgage calculator is estimating

This UK mortgage calculator is built for property-buying and remortgage-style planning where the borrower wants to understand the monthly commitment before talking to a lender in detail. It starts with the standard fixed-rate mortgage formula, then adds a clearer planning layer around loan-to-value, interest-only comparison, and regular home-ownership costs such as council tax, buildings insurance, and service-charge style fees.

That broader view matters because the lender-style repayment figure is only one part of the affordability picture. Searchers looking for a repayment mortgage calculator, interest-only mortgage calculator, or monthly mortgage repayments estimator are usually trying to answer a real budgeting question: how much cash leaves the household each month, what tax applies at purchase, and how sensitive the payment is to a higher rate.

This page is explicitly scoped to UK purchase planning. It uses GBP examples, UK terminology, and region-specific residential transaction-tax bands. It is not a universal global mortgage tool and it does not try to model tax rules outside the United Kingdom.

How the repayment and interest-only calculations work

For a repayment mortgage, the calculator uses the standard fixed-rate amortisation formula to turn the loan amount, monthly interest rate, and number of monthly payments into one level principal-and-interest payment. That payment gradually clears both the interest and the capital balance over the stated term, which is why the balance due at the end of the term is zero in the repayment column.

For an interest-only mortgage, the monthly payment is much simpler: the monthly interest rate is applied to the loan amount and only that interest is paid each month. The capital balance is not reduced by those monthly payments, which is why the calculator keeps the full loan amount visible as the balance still due at the end of the term. That distinction is central to interpreting the lower monthly figure honestly.

The rate-stress table then reruns the same loan size over the same term at the entered rate, plus one percentage point, and plus two percentage points. It is not predicting future mortgage rates. It is simply showing how sensitive the payment would be if the same borrowing had to be carried at a higher fixed rate later.

Stamp duty, LBTT, and LTT are purchase-cost context, not monthly mortgage cost

The calculator keeps purchase tax separate from the monthly mortgage result because these costs answer different planning questions. Stamp Duty Land Tax (SDLT) in England and Northern Ireland, Land and Buildings Transaction Tax (LBTT) in Scotland, and Land Transaction Tax (LTT) in Wales are one-off acquisition taxes. They affect how much cash you need at completion, but they do not form part of the monthly mortgage repayment itself.

Regional treatment also matters. England and Northern Ireland currently use SDLT bands with first-time buyer relief up to £500,000 and an additional-property surcharge on top of the normal rates. Scotland uses LBTT with a modest first-time buyer nil-band increase and a separate Additional Dwelling Supplement. Wales uses main residential LTT bands and separate higher residential rates for additional properties, but it does not use a distinct first-time buyer residential band in the same way England does.

That is why the result table shows both the detailed tax-band breakdown and any relief or surcharge relative to the standard residential bands. A first-time buyer in England may see a relief amount, while a Scottish or Welsh additional-property buyer will usually see a larger surcharge line. These one-off taxes should be budgeted alongside deposit, legal fees, valuation fees, and moving costs rather than treated as part of the mortgage payment.

Worked example: 425,000 purchase with a 20% deposit

Suppose you enter a 425,000 property price, an 85,000 deposit, a 25-year term, and a 5.2% rate. The loan amount becomes 340,000 and the LTV is 80%. On the repayment basis, the monthly mortgage figure is materially higher than the interest-only figure because the repayment option is clearing both capital and interest over the term. Once council tax and buildings insurance are added, the real monthly housing cost becomes higher again than the lender-style headline alone suggests.

If the same buyer is purchasing in England as a home mover, the purchase-tax line uses the standard SDLT residential bands. Switching the buyer type to first-time buyer can reduce the one-off tax bill, while switching to an additional-property purchase can increase it sharply because the higher rates apply. That is exactly the kind of comparison many buyers miss when they focus only on the monthly mortgage number.

The stress table is useful here too. A payment that feels manageable at 5.2% can look materially tighter at 6.2% or 7.2%. This does not mean those rates will happen. It means a buyer can test whether the margin in their monthly budget is robust enough before they commit to a mortgage or a product transfer path.

What this UK mortgage calculator does not cover

This calculator is a fixed-rate planning tool. It does not model product fees added to the loan, rate changes at the end of a two-year or five-year deal, lender stress tests, broker fees, legal fees, early repayment charges, offset structures, or unusual mortgage products. If those features matter to your quote, the result here should be treated as an early planning estimate rather than a final borrowing decision.

It also does not decide whether a lender will actually approve the mortgage. Real underwriting depends on income, outgoings, credit profile, employment status, deposit evidence, and lender-specific policy. A borrower comparing borderline affordability scenarios, interest-only eligibility, or complex tax positions should use this page as a preparation tool and then confirm the numbers with the lender, broker, or an independent financial adviser.