Stamp Duty Land Tax, SDLT, is what you pay HMRC when you buy a home in England or Northern Ireland. It works like income tax bands: each rate applies only to the slice of the price inside its band. For a main home the GOV.UK rates are nothing up to £125,000, 2% on the part to £250,000, 5% to £925,000, 10% to £1.5 million and 12% above.
On a £400,000 house that gives nothing on the first £125,000, £2,500 on the next £125,000 and £7,500 on the last £150,000, so £10,000 in all. A rate is never applied to the whole price, so a purchase a pound over a threshold costs only a few pence more than one a pound under it.
Two adjustments matter most. First-time buyers pay nothing up to £300,000 and 5% on the portion from £300,001 to £500,000, but lose the relief entirely if the price is over £500,000: the same £400,000 house would cost them £5,000. And if the purchase means you will own more than one home, you usually pay 5% on top of every band.
Scotland and Wales do not use SDLT. A Scottish purchase pays Land and Buildings Transaction Tax to Revenue Scotland, and a Welsh one pays Land Transaction Tax to the Welsh Revenue Authority, each with its own bands, so the same price can carry quite different tax across the border.
The mortgage calculator and the rent vs buy calculator charge the standard SDLT bands for a main home on a British purchase and add the result to the cash you need on completion. First-time buyer relief and the additional-property surcharge are not modelled, so a first-time buyer's real bill can be lower than the figure shown.