The arithmetic

On a second home the surcharge sits on top of the standard bands, and it applies to the whole price rather than the slice above a threshold. On a £900,000 purchase that difference is the single largest line in the completion statement after the price itself.

Two reliefs get missed. If you are replacing a main residence and the sale completes within the window, the surcharge is refundable — buyers routinely pay it and never claim it back. And a property with a genuinely separate self-contained annexe may qualify for multiple dwellings treatment.

Neither is a loophole. Both need the paperwork in order before exchange, which is a conversation for your solicitor in week one, not week six.