Build Budget Pro | Construction Cost Calculator

Know your numbers before you build

The construction cost calculator designed by architects, for homeowners. Get accurate UK estimates and discover where you can save.

2025 pricing
RIBA-aligned
2,400+ users
7-Day Access
£ 19
One-time payment • Instant access
  • Unlimited calculations
  • Region-specific UK pricing
  • Professional breakdown emailed
  • Personalised cost-saving tips
  • Book £145 strategy session (creditable)

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7 days left

Let's estimate your build

Answer these questions to get an accurate cost estimate.

1

How big is your project?

Enter the total internal floor area you're adding or converting.

25 m²
10 m²80 m²150 m²
Typical sizes
  • Small rear extension: 15-20 m²
  • Kitchen-diner: 25-40 m²
  • Wraparound: 35-50 m²
  • Loft conversion: 25-40 m²
2

What are you building?

Select the type that best matches your project.

🏡
Rear Extension (Single Storey)
Kitchen-diner, open plan
from £900/m²
🏠
Rear Extension (Double Storey)
Ground + bedroom above
from £1,300/m²
🔄
Wraparound Extension
Side return + rear combined
from £1,100/m²
🔺
Loft Conversion
Dormer, mansard, Velux
from £1,400/m²
🚗
Garage Conversion
Transform unused space
from £800/m²
⬇️
Basement Conversion
Dig out or lower cellar
from £2,200/m²
🏗️
New Build House
Ground-up construction
from £1,800/m²
3

Where's your project?

Location significantly affects labour and material costs.

🏙️
London
Highest UK costs
+35%
🌳
South East
Surrey, Kent, Sussex
+18%
🌊
South West
Bristol, Devon, Cornwall
+12%
🏭
Midlands
West & East Midlands
+5%
🏔️
North West
Manchester, Liverpool
+8%
⚓
North East / Yorkshire
Newcastle, Leeds, Sheffield
Baseline
🏴󠁧󠁢󠁳󠁣󠁴󠁿
Scotland
Edinburgh, Glasgow
-5%
🏴󠁧󠁢󠁷󠁬󠁳󠁿
Wales
Cardiff, Swansea
-8%
4

What finish level?

This affects materials, fixtures and finishes throughout.

🔨
Essential
Good basics, budget-conscious
Baseline
🏠
Comfortable
Quality materials, most popular
+25%
✨
Premium
Designer finishes, high-end
+50%
💎
Luxury
Bespoke everything
+100%
5

What's included?

Select all that apply to your project.

Structural work (steels, foundations)
Most extensions need this
£8,000+
New kitchen
Units, worktops, appliances
£15,000+
Bathroom / En-suite
Suite, tiling, plumbing
£8,000+
Underfloor heating
Water-based system
£4,000+
Bi-fold or sliding doors
3-4m aluminium doors
£6,000+
Roof lights / skylights
Natural light from above
£3,500+
Garden / landscaping
Patio, fencing, planting
£5,000+
6

Professional fees?

Architects, engineers and building control are essential.

Architectural services
Design, planning, building regs
~10%
Structural engineer
Calculations, beam specs
£3,000
Building control
Inspections and sign-off
£1,500
Party wall surveyor
Required near boundaries
£2,500

Contingency allowance

15%
10% (new build)15% (typical)25% (older property)