Build Cost Calculator
Get an instant estimate for your extension, loft conversion, refurbishment or new build based on real 2026 London construction rates.
What kind of project are you planning?
Use this calculator to get an instant cost estimate for your project. We'll ask a few quick questions, then show you a breakdown based on 2026 London build rates.
What type of property is it?
Where is the property?
Is the property in a conservation area or listed?
What level of finish are you looking for?
What is the approximate floor area?
Enter the total new floor area in square metres. For extensions, this is the footprint of the new addition. For loft conversions, it's the usable floor area at head height. For refurbs, it's the total area being refurbished.
Not sure? Typical rear extension: 20–40m². Dormer loft: 20–35m². Full house refurb: 80–200m².
Will you be adding any of the following?
Before we show your cost estimate…
Share a few details and we'll email you a full summary of your cost estimate plus next steps for your project.
Your estimated build cost
FAQs
Does this include professional fees?
No. The estimate covers build cost only. Professional fees — architectural drawings, structural engineering, building regulations, planning and party wall — are separate and typically add 10–15% on top of the build cost.
Does it include VAT?
No. All figures exclude VAT. New builds may qualify for zero-rated VAT on construction costs. Extensions and refurbishments are standard-rated at 20%.
How accurate is this estimate?
These are indicative ranges based on 2025 London market rates. Actual costs depend on site conditions, structural complexity, contractor selection and detailed specification. For a formal cost plan, you should commission a Chartered Quantity Surveyor alongside your architect.
What's included in the build cost?
The build cost covers all construction works — groundwork, structure, roofing, external envelope, internal fit-out, MEP (mechanical, electrical and plumbing), finishes, and fixtures. It does not include demolition, abnormal site costs, external works, landscaping, furniture or loose equipment.
Important: This estimate is for guidance only and does not constitute a quotation. Figures exclude VAT, all professional fees, statutory fees, party wall costs, planning obligations and abnormal site costs. Always obtain a formal cost plan before committing to a project budget.
Did you know that building costs in London and the UK are the second highest in the world and rising fast? Whether you’re planning a self build, a new build house or a major extension, understanding the average cost to build is the first step to setting a realistic budget for your project.
This cost guide covers UK construction costs in 2025, with a full cost breakdown by region, specification and project type. All costs are based on current building rates drawn from BCIS (Building Cost Information Service) construction cost data and our own live data from build projects across London and the UK. Use our free construction cost calculator above to help you estimate your total cost instantly.
What Determines the Cost of Building a House?
When it comes to building your new home, the cost will depend on three main factors.
1) Building design the design of your project has a direct impact on cost. Complex roof forms, partition layouts, large spans and multiple storeys all add cost compared to a simple footprint. Conservation area and listed building constraints typically add 10–30% to building works costs due to the requirement for specialist materials and heritage-led design. If you need early cost advice, our team offer a free 30-minute consultation — book a slot using the calendar on this page.
2) Fittings and material finishes your specification level is one of the biggest drivers of overall cost. A standard-specification build project uses builder-grade fittings throughout. A good-specification project uses mid-range materials with considered design choices. An excellent-specification project features bespoke joinery, high-end fittings and premium finishes throughout. The difference between standard and excellent specification may cost 40–60% more on the same gross internal area.
3) Project management appointing an experienced project manager or architect to administer the contract is one of the most effective ways to save the cost of variations and control the build process. Traditional procurement — where building works are put to competitive tender against a complete set of drawings — typically delivers the best value for a self build or new build house project.
House Build Cost Per Square Metre in the UK
The figures below are based on 2025 tender prices from the BCIS tender price index. All costs are based on gross internal area (GIA), also referred to as gross floor area. These UK construction costs exclude VAT, professional fees and abnormal site costs.
| Region | Standard (£/m²) | Good (£/m²) | Excellent (£/m²) |
|---|---|---|---|
| Inner London | £2,100 – £2,600 | £2,600 – £4,200 | £4,200 – £6,500+ |
| Outer London | £1,800 – £2,200 | £2,200 – £3,500 | £3,500 – £5,500+ |
| South East | £1,600 – £1,900 | £1,900 – £3,000 | £3,000 – £4,800+ |
| North West | £1,200 – £1,500 | £1,500 – £2,500 | £2,500 – £4,000+ |
| East of England | £1,300 – £1,600 | £1,600 – £2,700 | £2,700 – £4,200+ |
| West Midlands | £1,200 – £1,500 | £1,500 – £2,500 | £2,500 – £4,000+ |
| South West | £1,300 – £1,600 | £1,600 – £2,600 | £2,600 – £4,100+ |
For reference, the equivalent cost per square foot ranges from approximately £185 – £240/ft² at standard specification in Outer London, rising to £390 – £600/ft² at excellent specification in Inner London. These building prices reflect the latest cost information available from the UK construction industry.
Average Cost to Build by Number of Bedrooms
The complete cost below covers building works only and is based on typical gross internal area for each house type.
2 bedroom house (70–90m²): £105,000 – £500,000+ depending on specification and location. Average cost at good specification in London: £140,000 – £280,000.
3 bedroom house (90–120m²): The average cost to build a 3 bedroom house in the UK sits at £180,000 – £420,000 at good specification. In London, the total cost typically ranges from £350,000 – £550,000.
4 bedroom house (130–180m²): Total cost at good specification ranges from £260,000 – £600,000. In Inner London, a well-specified 4 bedroom new build house may cost in excess of £700,000 in building works costs alone. Use the calculator above for early cost advice on your specific project.
5 bedroom house (180–250m²+): The range of costs at good specification runs from £360,000 – £850,000. At this scale, an experienced project manager will typically save more than their fee through rigorous contract administration during the build process.
Cost Breakdown: Where Will Your Budget Go?
On a typical new build house or major extension in London and the UK, the overall cost breaks down broadly as follows. These costs reflect current building rates and are consistent with BCIS elemental cost data.
- Substructure and groundwork: 10–15% of build cost. Ground conditions, proximity to trees and high water tables must all be factored in the costs at an early stage.
- Structure (walls, beams, columns, partition walls, floors): 20–30% of build cost.
- Roofing and external envelope (cladding, windows, doors): 15–20% of build cost. The choice of fittings and material finishes here significantly affects the range of costs.
- MEP (heating, plumbing, electrics, ventilation): 15–20% of build cost.
- Internal finishes and fit-out (joinery, kitchen, bathrooms, decoration): 25–35% of build cost at good to excellent specification.
Additional Costs to Cover
These costs are separate from building works and must be included in your budget for your project:
- Professional fees (architecture, structural engineering, building regulations drawings, party wall surveyor): typically 10–15% on top of construction cost
- VAT: 20% on extensions and refurbishments; new build house projects may qualify for zero-rated VAT
- CIL: charged by many London boroughs on new gross floor area — Westminster and RBKC rates are among the highest in the UK
- Contingency: minimum 10% on the build cost; 15–20% for projects involving existing buildings or heritage constraints
FAQ
Are construction costs still inflated post-pandemic?
Yes. UK construction costs in 2025 remain materially above the 2022 baseline and significantly higher than pre-pandemic levels. The BCIS tender price index continues to show positive inflation, driven by labour shortages across the UK construction industry. Building prices are not expected to fall significantly in 2026.
Will construction costs go down in 2026?
Most forecasters expect cost inflation of 2–4% in 2026. Labour costs are unlikely to fall given structural skills shortages. If you are planning a build project, delaying in anticipation of lower building prices is unlikely to be beneficial — the costs involved in delay typically outweigh any potential saving.
How much do builders charge per m²?
For London and the UK residential build projects in 2025, typical all-in building prices range from £1,400/m² for a standard-specification outer London extension to £6,500/m² or more for an excellent-specification inner London new build house. Use our construction cost calculator above for a project-specific estimate.
How can I calculate construction cost?
For early cost advice, use the construction cost calculator above to get an instant estimate based on your gross internal area, location and specification. For a complete cost plan, appoint a Chartered Quantity Surveyor once your architect has produced drawings — whether for a loft conversion, extension or new build.
All figures are based on 2025 UK construction cost data. Costs are based on gross internal area and current building rates. Actual costs will vary depending on site conditions, contractor selection and specification. Always commission a formal cost plan before committing to a project budget. AC Design Solution Ltd — CIAT Chartered practice providing architectural design, structural engineering, building regulations drawings, planning and party wall surveyor services across London and the UK. Call 0208 152 4006 or email sales@acdesignsolution.com.