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💰 How Much Will My Extension Cost?
Realistic cost estimates for UK house extensions — build cost, planning fees, professional fees, and everything in between.
Estimate Your Extension Cost
About this tool: Extension Cost Guide
Guide to what an extension really costs — build cost ranges by type and size, plus the planning, technical and professional fees on top.
When to use it
Use early to budget a householder project realistically before design work starts.
Policy and guidance it draws on
Reference
Part of Financial Intelligence
Use these tools to understand the financial side of your project — what fees you'll pay, whether the scheme is viable, what CIL/S106 might cost, and whether your land value assumptions stack up. Essential for go/no-go decisions.
Related tools
Fee CalculatorViability AssessmentBuild Cost EstimatorDev AppraisalCIL & S106Affordable HousingLand ValueCIL Exemption CheckerGuidance to help you prepare — not formal planning advice. Check the current policy text and your council's local plan before relying on it.