Calculate Your House Extension Cost | Extension Price Calculator

What are you planning?

Choose the closest type. You can come back and change this later.

Extension type

Rear extensionMore room at the back of your home Side extensionBuild out to the side Wrap-aroundCombine rear and side space Kitchen extensionExtra space for a kitchen or dining area

How many storeys?

Single storeyOne level of extra living space Two storeysExtra space on the ground and first floors

How much space will you add?

Rough measurements are fine for now. We use external dimensions to estimate overall floor area.

Approximate width

metres

Across the back or side of the house

Approximate depth

metres

How far it projects out

Your estimated new floor area: 15.0 m²
Smaller schemes can cost more per m² because they still need foundations, site setup and professional work.

Where and how will you build?

Location, finish and site conditions can all affect a contractor's price.

Your UK regionWe use broad regional planning adjustments, not postcode quotes.

Finish levelIncludes standard internal finishes, not a new kitchen.

How easy is it to reach the work area?

Fairly easyReasonable access for materials and tradesRestrictedNarrow access or difficult deliveries

Are there known ground challenges?

Not sure / none knownAssume standard conditionsYes, potentiallyPoor ground, slopes or unusual foundations

Any extra features?

Select only the items you expect to include. Standard windows, an external door and ordinary finishes are already part of the baseline.

Number of rooflightsAdded as an upgrade to standard roofing

Optional additions

Bifold door upgradeUpgraded wide glazing in place of standard door Large structural openingAllowance for additional steelwork into the old house New fitted kitchenSeparate provisional supply and installation allowance New bathroom / WC fit-outSeparate provisional plumbing and fitting allowance Drainage diversionProvisional allowance for moving drains

Good to know: Unforeseen structural work or ground conditions can cost considerably more than these allowances. Your final report includes a contingency.

Your project summary

Review the details before continuing. You will get a low, expected and high estimate with a full breakdown.

Personalised estimate & PDF

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Local preview: The next button opens a full sample report without charging you. On the live site, this step will open secure Stripe checkout.

Let's work out your budget

What are you planning?

How much space will you add?

Where and how will you build?

Any extra features?

Your project summary