Extension Cost Calculator

Enter your floor area, pick the type of extension, the finish you want and your region, and we'll estimate the build cost using current UK per square metre ranges. The single biggest swing on price is location: a London or South East build commonly costs 20 to 30 per cent more than the same job elsewhere, so region matters as much as size.

These figures are the cost to build, including labour, materials and a standard fit-out for the chosen finish. They do not include professional and statutory fees, which typically add another 10 to 15 per cent: architect or designer, structural engineer, planning application, building control and party wall surveyor where a neighbour's wall is involved. VAT at 20 per cent applies to most domestic extension work; it is already built into the rates below.