SDLT is calculated differently for residential and non-residential properties. For residential properties (e.g. house or flat), Stamp Duty Land Tax is typically paid on increasing portions of the property price at the time of purchase. The amount payable depends on when the property was bought and how much was paid for it. Find out what the SDLT residential rates are here.
The above also applies to non-residential & mixed land and properties. Stamp Duty Land Tax is paid on increasing portions of the property price when this is £150,000 or higher.