Extension cost calculator

The range above starts from our typical build rates: £2,200 to £2,500 + VAT per m² for a single-storey extension, with an additional £1,800 per m² for the upper floor on a double-storey extension. That covers the structural build itself, groundworks, structure, roofing, first and second fix, and a standard finish.

Bifold doors, roof lights, a rewire and underfloor heating are added on top using our own ballpark figures if you select them, so the range moves to reflect your choices. Roof type and underfloor heating are our own rough estimates rather than confirmed prices, since both vary a lot by design and spec, so treat those parts of the range as less certain than the rest.

It still doesn't include a kitchen or bathroom fit-out (these run from around £10,000 to well over £100,000 depending on specification, so we don't attempt to estimate it here), planning and building control fees, or VAT. Ground conditions and drainage can also move the price significantly in either direction, and we can only price those properly once we've seen the site.

Every job is different, and every contractor prices differently too, so treat this as a starting point for working out roughly what you're dealing with, not a number to compare quotes against line for line. See our guide on what actually drives an extension's cost up or down for more on this.