Describe your extension
Choose rear, side, wrap-around or kitchen, then add approximate width, depth and storeys.
Plan your project with confidence
Planning an extension?
Planning an extension?
Know your budget.
Find out what your house extension could cost before you speak to builders. Enter a few details, get a realistic planning range and understand where your money may go.
Calculate my extension price
UK cost benchmarks
Detailed cost breakdown
Instant PDF after purchase
From first idea to clearer budgetA useful starting point before quotes
Low, expected & highSee the possible range, not one misleading number
Transparent assumptionsBuild, fees, VAT and contingency shown separately
Yours to keepPrintable report for your early planning conversations
How it works
Clearer plans in three simple steps
No drawings or technical knowledge required. Start with the details you already know.
Fine-tune the specification
Select your UK region, finish standard, site access and upgrades such as rooflights or bifold doors.
Unlock your planning report
Review a breakdown of building work, professional allowances, VAT and a sensible contingency.
What's in your estimate
A budget that accounts for more than bricks
Small extensions, rooflights, structural openings and professional fees can change the overall project cost. We make those assumptions visible.
Construction and finishes
Foundations, structure, roof, insulation, typical glazing, electrics and basic internal finishes.
Common extras
Optional allowance for bifold upgrades, rooflights, structural steel, new kitchens and drainage diversions.
Hidden budget items
Indicative professional and approval fees, standard construction VAT and an allowance for surprises.
Cost model informed by the Federation of Master Builders' published extension-cost guide. Regional factors and extra allowances are our transparent planning assumptions, not verified contractor quotes.