Extension Cost Calculator With the extension cost calculator you can get a quick, free, rough estimate of at least some of the costs involved in building extra room (s) for your house. By entering information about the extensions external size, roof type, number of storeys and the UK location, an estimate of the building cost can be found. How much will an extension cost in 2025? In short, building a single-storey extension is likely to cost between £2,200-£3,300/m² of new internal space (excluding VAT).
So a 30m² single-storey kitchen extension could be estimated at somewhere between £66,000-£99,000, plus VAT at 20%. If that sounds rather general - that's because it is. House extension costs in the UK typically fall between £1,800 and £3,000 per square metre, depending on the finish, structure and location.
That means a modest 20m 2 extension can range from about £36,000 to £60,000+, excluding premium kitchens, bathrooms and bespoke glazing. House extension costs: Breakdown by size & type House extension costs vary hugely depending on the size, type and complexity of your project and where you live. We explain how much house extensions cost, including all the fees you may need to pay, and how to save money.
Get 3 offers. How much does house extensions cost? UK extension costs vary widely depending on size, materials, and complexity. Industry data suggests that a single-storey rear extension starts from around £1,500 per square metre for a simpler build, while a more typical range is £1,800-£2,500 per square metre.
Looking to build an extension in 2026? Discover the latest costs per square metre for extensions in the UK and factors that affect pricing. What's the average cost of a house extension in 2025? Read the latest cost guidance from Checkatrade. A simple guide to estimate your house extension cost.
Updated in 2025 with real survey data from residential architects on Design for Me. Find out the 2025 house extensions cost UK homeowners can expect. Learn about average prices, key factors, and tips to plan your extension.
Discover how much a house extension costs in 2025. Explore average prices, cost breakdowns, and budgeting tips to plan your perfect home upgrade with confidence.
