UK Mortgage Calculator

The calculator subtracts your deposit from the home price to get the loan amount, then applies the standard repayment formula: the annual rate divided by twelve gives a monthly rate, and the payment is set so that equal monthly instalments — 300 of them on the default 25-year term — repay the loan exactly, interest included. Early payments are mostly interest; the split shifts towards principal as the balance falls.

It also divides the loan by the price to give your loan-to-value ratio, and LTV is the number UK mortgage pricing runs on. The Bank of England compiles its official quoted-rate statistics from lenders' advertised products at five LTV points — 60%, 75%, 85%, 90% and 95% — with separate two-year and five-year fixed series at each, because that is how lenders shelve their products. High-LTV credit risk is priced into the interest rate itself, so the band you land in shapes the rates available to you.

Bands are ceilings. A borrower at 90.4% LTV cannot use a 90%-band product; they need a 95%-band one. On a £250,000 home, a £24,000 deposit gives 90.4% LTV, while £25,000 gives exactly 90% — £1,000 of extra deposit changes the shelf of products you can pick from. The calculator shows your exact LTV so you can see when a slightly larger deposit crosses a band boundary.

Take the calculator's defaults: a £250,000 price, a £37,500 deposit (15%), a rate of 4.5% and a 25-year term. The rate is a hypothetical chosen for the arithmetic, not a quote — rates move, so enter the one you have actually been offered.

The loan is £250,000 minus £37,500, or £212,500, and the LTV is £212,500 divided by £250,000: exactly 85%, right on a band boundary. The monthly rate is 4.5% divided by 12, or 0.375%, and the repayment formula gives a payment of £1,181.14 a month.

The first payment shows how repayment mortgages front-load interest: month one's interest is £212,500 × 0.375% = £796.88, so only £384.27 of that first £1,181.14 reduces the loan. The balance falls slowly at first and faster later, because each month's interest is charged on a smaller balance.

Two years in — a common deal length — the position is: £28,347 paid, of which £18,716 was interest and £9,631 principal, leaving £202,869 owing. That balance matters more than the 25-year totals, for reasons the next section covers.

The quoted rate on a UK mortgage is not for life. The standard structure is an introductory deal — most commonly a two-year or five-year fix, the two product types the Bank of England tracks in its quoted-rate statistics — after which the loan reverts automatically to the lender's Standard Variable Rate. The SVR is set by the lender, can change at any time, and is typically higher than deal rates, which is why the end of a deal is the standard trigger for remortgaging or taking a product transfer with the same lender. There is no mainstream UK equivalent of the American whole-term 30-year fixed rate.

Read the calculator's output accordingly. The 25-year totals describe a loan whose rate never changes; a real UK mortgage is a sequence of deals. The dependable figures are the ones inside the deal period: in the worked example, a two-year deal at 4.5% costs £28,347 in payments and leaves £202,869 owing — the position from which you shop for the next deal, at whatever rates then prevail.

Comparing deals is what the APRC exists for. UK mortgage cost disclosure uses the Annual Percentage Rate of Charge, calculated under the FCA's MCOB rules; it must appear in financial promotions, the ESIS illustration and the mortgage offer, and unlike the headline rate it folds fees in. Fees are material: arrangement fees of roughly £999 to £1,499 are conventional on mainstream deals, and lower-rate deals often carry higher fees. Adding a £999 fee to the example loan costs about £1,666 over the full term — £667 of it interest on the fee itself. The lowest headline rate is not automatically the cheapest deal; the APRC and the total cost over the deal period are the honest comparisons.

Twenty-five years is the traditional UK default — this calculator's, too — but it no longer describes the market. Bank of England analysis of regulatory data shows mortgages with terms of 30 years or more rose from 12% of new lending at the end of 2005 to 50% in early 2024, and around two-thirds of first-time buyers now borrow over terms of 30 years or longer, with many stretching to the common lender maximum of 40 years.

The mechanism is a plain trade. A longer term spreads the principal over more payments, so each month costs less; but the balance stays higher for longer, so more interest accrues in total. At the example loan of £212,500 and a constant 4.5%, the three most common term choices compare like this:

Stretching from 25 to 35 years cuts the payment by £175.47 a month and adds £68,038 of interest — roughly £388 of eventual interest for every £1 taken off the monthly payment. Neither answer is wrong; the term is a genuine lever. A term set long at the start can also be shortened later, by remortgaging onto a shorter one or by overpaying within your deal's allowance. Change the term field and the calculator recomputes both sides of the trade.

There is no PMI line because there is no US-style borrower-paid mortgage insurance in the UK. High-LTV credit risk is priced into the interest rate through the LTV bands, and under the permanent Mortgage Guarantee Scheme launched in July 2025 the government insures participating lenders on 91–95% LTV loans, with the lender paying the fee to HM Treasury. The borrower pays no insurance premium, so the calculator adds none.

The calculator prices a loan; it does not predict what a lender will offer you. There is no mandatory +3% stress test — the Bank of England withdrew that recommendation with effect from 1 August 2022. Lenders instead assess affordability under the FCA's MCOB responsible-lending rules: they must consider likely rate rises over at least the next five years (unless the rate is fixed for five or more) and must assume rates rise by at least 1 percentage point, setting their own stress rates within that framework. The widely quoted 4.5-times-income figure is a portfolio rule, not a personal cap: it limits how much of a lender's new residential lending may sit at a loan-to-income of 4.5 or higher (15%), rather than capping any individual borrower.

Overpayments have limits during a fix. Early repayment charges typically run from 1% to 5% of the amount repaid, commonly stepping down each year of the deal, and most fixed deals allow penalty-free overpayments of typically 10% of the outstanding balance per year — a lender convention that varies by product, not a statutory right.

Finally, the maths here is for a repayment mortgage. An interest-only mortgage pays only the interest each month — £796.88 on the example loan — so the payment is lower but the balance never falls, and the full principal is due at the end of the term.