Free Tool
Construction Cost Calculator
Get an instant cost range for extensions, loft conversions, refurbishments and new builds. Based on 200+ real UK projects.
1. What type of project?
2. Size (m²): 20 m²
Gross internal area of the new space
3. Specification level
4. Location
Estimated cost range for your project
Rear Extension · 20 m² · Mid-range spec · London (Inner)
Indicative estimate only. Excludes VAT, professional fees, planning costs, and contingency. Get a formal estimate for accurate figures.
Get a Detailed Estimate from £95What affects construction costs in the UK?
Location
London and the South East typically cost 20–40% more than the Midlands or North due to higher labour rates and logistics.
Specification level
Finishes, glazing, kitchen and bathroom quality account for 20–40% of total project cost. Spec decisions matter more than size.
Structural complexity
Steelwork, underpinning, ground conditions and structural openings all add cost that calculators cannot fully capture.
Planning & compliance
Building Regulations, party wall matters, planning conditions and CDM compliance all affect programme and cost.
Disclaimer: These figures are indicative estimates for budgeting purposes only and are not formal quotations. Actual costs will vary based on site conditions, specification, procurement route, and contractor. Figures reflect typical market rates in 2026. Always obtain a site-visit quotation before committing to a budget.
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