Stamp duty, including the bits that catch people out.

Stamp duty isn't one tax. England and Northern Ireland pay Stamp Duty Land Tax (SDLT); Wales pays Land Transaction Tax (LTT); Scotland pays Land and Buildings Transaction Tax (LBTT). The thresholds and rates differ in each, so a "UK stamp duty" calculator that only knows SDLT is wrong the moment you cross a border.

The additional-dwelling surcharge is the biggest trap. In England and NI it's an extra 5% on every band (so even the portion under £125,000 is taxed). In Wales the higher rates start at 5% from the first pound. In Scotland it's the 8% Additional Dwelling Supplement on the whole price. It applies if you'll own more than one home at completion and aren't replacing your main residence — and you can often reclaim it if you sell your old main home within 36 months.

First-time-buyer relief has a catch. In England and NI you pay nothing up to £300,000 and 5% on the slice to £500,000 — but the relief vanishes entirely if the price is over £500,000, so a £505,000 purchase is taxed at the standard rates on the whole lot. Scotland gives first-time buyers a higher £175,000 nil-rate band. Wales has no first-time-buyer relief at all — its higher starting threshold applies to everyone.

If you're not UK-resident for the surcharge's purposes — broadly, you've spent fewer than 183 days in the UK in the 12 months before completion — England and NI add a further 2% on every band, on top of any additional-dwelling surcharge. Wales and Scotland have no equivalent. The surcharge can be refunded if you later become UK-resident in the relevant period.

All three taxes are progressive: each rate applies only to the slice of the price within its band, not the whole price. The breakdown above shows exactly which slice is taxed at which rate.