Work out your mortgage payment on a UK purchase price, deposit, rate, and term, along with the Stamp Duty Land Tax due — calculated in the same marginal bands HMRC uses, with first-time buyer relief applied if you tick the box.
How to Use the UK Mortgage Calculator
Purchase price, deposit, rate, and term calculate the monthly repayment; tick "First-time buyer" if it applies, since it changes how the Stamp Duty figure below is worked out, not the mortgage payment itself.
UK repayment mortgages compound monthly, same as the payment schedule — no special adjustment needed here, unlike a Canadian mortgage's semi-annual quirk:
M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ − 1]P is the loan amount (purchase price minus deposit), r the monthly rate, n the number of monthly payments. The more interesting number on this page has nothing to do with the mortgage at all: Stamp Duty Land Tax.
SDLT Is a Marginal Tax, Not a Slab Tax
Since a 2014 reform, SDLT on a residential purchase in England and Northern Ireland works in bands, the same way income tax brackets do — only the slice of the price sitting inside each band gets taxed at that band's rate, not the whole price at whichever band it falls into.
£0 – £125,000: 0%
£125,001 – £250,000: 2%
£250,001 – £925,000: 5%
£925,001 – £1,500,000: 10%
above £1,500,000: 12%A £300,000 purchase, worked through the bands, owes nothing on the first £125,000, 2% on the next £125,000 (£2,500), and 5% on the remaining £50,000 (£2,500) — £5,000 total, not 5% of the full price.
First-Time Buyer Relief Has a Cliff Edge
Check the first-time buyer box and the bands change: 0% up to £300,000, then 5% from £300,001 up to £500,000. That's a genuinely better deal — zero duty on a £300,000 first home instead of £5,000.
But the relief has a hard ceiling. Cross £500,000 and it doesn't taper or partially apply — it switches off entirely, and the purchase falls back to the standard bands above as though the buyer had ticked nothing at all. A first-time buyer purchasing at £499,999 pays SDLT under the generous bands; the same buyer at £500,001 pays it under the standard ones, a difference running into thousands of pounds over a two-pound difference in price. It's one of the sharper cliff-edges in UK property tax, worth knowing about before offering a round number right at the boundary.