Building & home improvement cost guide
House Extension Cost Calculator UK
Estimate UK house extension costs by new floor area, finish and region before speaking to designers and builders. These figures are planning guidance rather than a supplier quotation.
Example for a 25 m² extension with a standard finish in Norfolk or Suffolk.
Adjust it for your project
JobPrice uses a baseline of £2,100–£3,500 per m², with a minimum project allowance, then adjusts for finish and UK region.
Calculate my house extension costWhat changes the price?
- Single- or two-storey construction
- Ground conditions and drainage changes
- Glazing, kitchens and internal finishes
- Structural openings into the existing home
- Design, surveys and statutory approvals
Before comparing quotes
- Ask which professional and approval fees are excluded.
- Confirm foundations, drainage and structural openings.
- Keep a contingency for ground conditions and variations.
Compare the same scope, specification and exclusions across every quote. Keep a contingency for changes and hidden conditions.
How to build a reliable house extension price
JobPrice uses a baseline of £2,100–£3,500 per m², with a minimum project allowance, then adjusts for finish and UK region.
Use measured quantities and a written specification, then compare the same inclusions, exclusions and finish level across every contractor quote.
Method note: JobPrice benchmarks are broad planning models, not live supplier quotes. Confirm current local rates, tax, regulation, access and the final specification. Read the full pricing methodology.
How is the house extension estimate calculated?
JobPrice uses a baseline of £2,100–£3,500 per m², with a minimum project allowance, then adjusts for finish and UK region.
Is this house extension range a final quote?
No. It is an early planning range. A final quote should use the exact scope, current local rates, applicable tax, access conditions and any legal or professional requirements.
How can I get a more accurate house extension price?
Use measured quantities and a written specification, then compare the same inclusions, exclusions and finish level across every contractor quote.