Free Tools
Construction Cost Calculators
Get an instant ballpark figure for your project. Four free calculators built on current UK construction rates — no sign-up required.
House Extension Cost Calculator
Single storey, double storey, side return and wrap-around extensions
Estimated construction cost (excl. VAT)
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Excludes VAT (20%), architect fees, planning application, building control, party wall agreements, structural engineer, and any groundworks surprises. Add 10% contingency for unforeseen costs.
Get a proper estimate from your drawings →Rates used in this calculator (updated October 2026)
| Type | Basic | Mid-range | High spec |
|---|---|---|---|
| Single Storey Rear Extension | £1,280–£1,800 | £1,700–£2,400 | £2,380–£3,360 |
| Double Storey Extension | £1,100–£1,560 | £1,490–£2,100 | £2,120–£3,000 |
| Side Return Extension | £1,360–£1,920 | £1,780–£2,520 | £2,550–£3,600 |
| Wrap-Around Extension | £1,440–£2,040 | £1,960–£2,760 | £2,720–£3,840 |
Cost per m² for the Midlands (regional multiplier 1.00). Multiply by your region’s figure in the table below.
Loft Conversion Cost Calculator
Velux, dormer, hip-to-gable and mansard conversions
Estimated construction cost (excl. VAT)
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Excludes VAT (20%), architect or designer fees, structural engineer, building control, party wall agreements and any staircase alterations to lower floors. Add 10% contingency for the unexpected.
Get a proper estimate from your drawings →Rates used in this calculator (updated October 2026)
| Type | Basic | Mid-range | High spec |
|---|---|---|---|
| Velux / Roof Light | £680–£960 | £940–£1,320 | £1,280–£1,800 |
| Dormer | £1,020–£1,440 | £1,360–£1,920 | £1,870–£2,640 |
| Hip-to-Gable | £1,100–£1,560 | £1,490–£2,100 | £2,040–£2,880 |
| Mansard | £1,280–£1,800 | £1,700–£2,400 | £2,380–£3,360 |
Cost per m² for the Midlands (regional multiplier 1.00). Multiply by your region’s figure in the table below. Minimum project costs apply: Velux £15,000, dormer £30,000, hip-to-gable £35,000 and mansard £50,000 before the regional adjustment.
New Build Cost Calculator
Detached, semi-detached, terraced houses and apartments
Estimated construction cost (excl. VAT & land)
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Excludes land purchase, VAT (typically zero-rated for new builds), architect fees, structural engineer, planning application, building control, utility connections, landscaping and external works. Add 5–8% contingency for a new build on a surveyed site.
Get a proper estimate from your drawings →Rates used in this calculator (updated October 2026)
| Type | Basic | Mid-range | High spec |
|---|---|---|---|
| Detached House | £1,580–£2,120 | £1,940–£2,600 | £2,640–£3,540 |
| Semi-Detached House | £1,410–£1,890 | £1,760–£2,360 | £2,380–£3,190 |
| Terraced House | £1,320–£1,770 | £1,670–£2,240 | £2,290–£3,070 |
| Flat / Apartment | £1,760–£2,360 | £2,290–£3,070 | £3,080–£4,130 |
Cost per m² for the Midlands (regional multiplier 1.00). Multiply by your region’s figure in the table below. Bungalows are adjusted up 8% and three-storey houses down 4%, reflecting shared foundations and roofs.
Basement Cost Calculator
New excavated basements and existing cellar conversions
Estimated construction cost (excl. VAT)
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Basement costs vary significantly depending on ground conditions, proximity to neighbouring foundations, water table depth, party wall obligations and access for excavation. These figures include excavation, waterproofing, structure and basic fit-out only. Add 15–20% contingency — basement projects regularly encounter unforeseen ground issues.
Get a proper estimate from your drawings →Rates used in this calculator (updated October 2026)
| Type | Basic | Mid-range | High spec |
|---|---|---|---|
| New Excavated Basement | £2,120–£3,000 | £2,980–£4,200 | £4,250–£6,000 |
| Existing Cellar Conversion | £1,020–£1,440 | £1,530–£2,160 | £2,210–£3,120 |
| Lowering / Underpinning Existing | £1,530–£2,160 | £2,210–£3,120 | £3,230–£4,560 |
Cost per m² for the Midlands (regional multiplier 1.00). Multiply by your region’s figure in the table below. Minimum project costs apply: new basement £60,000, cellar conversion £25,000 and lowering £40,000 before the regional adjustment.
Regional multipliers used in every calculator
| Region | Multiplier |
|---|---|
| London | ×1.30 |
| South East | ×1.15 |
| South West | ×1.05 |
| Midlands | ×1.00 |
| North of England | ×0.90 |
| Scotland | ×0.92 |
| Wales | ×0.88 |
| Northern Ireland | ×0.85 |