Free build, extension and renovation cost calculators.
Work out what your build, extension or renovation could cost, how long it will take and what to tell your architect, before you spend anything. Built from more than 600 projects, priced by a quantity surveyor, and not attached to anything we sell.
The Self Build Cost Calculator
A real number for your build, not a range wide enough to be useless. It includes the costs most people leave out.
Cost your build ↗New
The Extension Cost Calculator
What your extension is likely to cost, priced by a quantity surveyor in September 2026 and adjusted for your region, the age of the house, fees, contingency and VAT.
Cost your extension ↗New
The Renovation Cost Calculator
Four refurbishment bands, from a light refresh to a full strip-out, priced by a quantity surveyor in September 2026. Gets you to the right order of magnitude, with an honest list of what it cannot know.
Cost your renovation ↗
The Architect Brief Creator (free brief template)
Answer eight sets of questions and get a written brief you can send straight to a designer. The difference between a good first meeting and an expensive one.
Write your brief ↗
The Build Timeline Planner
Put in the date you want to start and see when you get on site and when you move in, based on how long these things actually take.
Work out your dates ↗New
The Plot Appraisal Checklist
Forty checks on one plot — planning, access, ground, services, title and cost — in the order you actually answer them. Leave with a written list of what could stop it and what to chase before you offer.
Appraise your plot ↗Self Build in Twelve Stages
The whole process in order: what happens at each stage, the mistake that costs most, and the piece of paper that proves you have finished it. Read it start to finish before you do anything, then keep it beside you.