Self build budget questions, answered.
Short, sourced answers to the money questions we had on our own build. Each page starts with the short answer, then the detail.
What will it cost?
How do I budget a self build? A seven-step method
Budget a self build in seven steps: a ranged estimate, UK build stages, compared quotes, tracked payments, live reconciling, VAT records and a final check.
How much does it cost to build a house in the UK per m²?
Build It puts the average UK self build at £2,500-£3,000 per m² of internal floor area in 2026, from about £2,200 for simple builds to £3,200+ high spec.
What's not included in the cost per m² of a self build?
Cost per m² covers building the house. Land, fees, warranty, insurance, connections, CIL, landscaping, finance, living costs and contingency all sit on top.
How much does it cost to build a 100m² house?
Using Build It's 2026 rates, a 100m² self build costs roughly £220,000 to £320,000+ to build, with £250,000 to £300,000 typical. Land and fees are extra.
How much does it cost to build a 150m² house?
On Build It's 2026 rates, a 150m² self build costs about £330,000 to £480,000+ to build, with £375,000 to £450,000 typical. Land and fees are extra.
How much does it cost to build a 200m² house?
Build It's 2026 guide puts a 200m² self build at roughly £440,000 to £600,000 to construct, and £640,000+ at high spec. Land, fees and VAT are separate.
How much does it cost to build a 250m² house?
Using Build It's 2026 rates, a 250m² self build costs about £550,000 to £800,000+ to construct, with £625,000 to £750,000 typical. Land and fees are extra.
Keeping it under control
How much contingency should I allow on a self build?
Allow 10-20% contingency on a self build. Some lenders ask for evidence of 15%, and renovations, unknown ground or complex designs need the higher end or more.
Why do self builds go over budget, and how do I stop it?
Self builds go over budget through low starting figures, missing items, mismatched quotes, upgrades, ground and VAT confusion. Track projected cost per line.
How do I compare builders' quotes that cover different things?
Compare builders' quotes by mapping each to the same build stages, listing inclusions and exclusions, separating VAT and allowances, then comparing by stage.
Cash flow and lenders
How do I plan cash flow on a self build?
Map every payment to a build stage and week, plan for early system deposits, retentions and VAT you can't reclaim until after completion, and keep a cash buffer.
Advance or arrears stage payment mortgage: what's the difference?
Arrears mortgages pay out after each build stage is done and valued, so you fund the work first. Advance mortgages pay at the start of a stage and usually cost more.
What do lenders want to see in a self build budget?
Lenders want costings, plans and a contingency, often a 10-year structural warranty, stage-by-stage cash flow and quotes as evidence.
Choosing a tool
What's the best app to manage a self build budget in the UK?
A spreadsheet, Build It's calculator and estimates, household budget apps or Self Build Budget: what each does, who it suits and what it costs for a UK self build.
Self build budget spreadsheet: is there something better?
A spreadsheet works for a self build budget if it has budget, quoted, committed, paid, projected and VAT columns per stage. An app helps when it gets busy.
Can I talk to my build budget in ChatGPT or Claude?
Yes. On the Professional plan, Self Build Budget connects to Claude, ChatGPT and other assistants via MCP, so you can ask about stages, quotes and VAT.