Most self-builds go wrong here — not on site, but eighteen months earlier, on a number somebody guessed. This gives you a defensible early-stage range, and shows you the costs people forget until the money has gone.
What this is. A feasibility estimate, not a cost plan. It gets you to a realistic budget and a sensible plot offer. Before you commit to a builder you need a measured Bill of Quantities — that is the only number you can hold someone to. We have nothing to sell you in these figures: Self Build Mentor is paid by self-builders, not by suppliers.
Step 1
Your build
Internal floor area of everything heated — all storeys added together.
A typical UK self-build is 180–250 m². Type an exact figure if you have drawings.
Regional factors reflect labour rates and access, not land values.
Step 2
Shape and complexity
The drawings decide more of your budget than the fittings do. Tick what applies.
Priced at £2,800/m² — excavation, tanking, retaining structure.
Indoor pool and plant runs £75,000 upwards. Outdoor is roughly half.
Step 3
Energy standard and renewables
Specification level covers what you see. This covers what you don't — fabric, airtightness and plant.
About £1,500 per kWp on a new build with the scaffold already up. 4 kWp is a common domestic array.
Step 4
Everything that isn't the house
This is where budgets break. Defaults are typical — change them if you know better.
Architect, engineer, QS, building control. Industry guidance is 8–15%.
Drive, patios, fencing, planting, drainage runs beyond the house.
Typically £10,000–£25,000. More if you are far from a main.
Guidance is 10–15%. Below 10% on a first build is optimism, not budgeting.
Step 5 · optional
The plot
Add it to see the whole project, or leave blank if you already own the land.
Conveyancing and searches. Add SDLT/LBTT if it applies to you.
Where the money goes
Your breakdown
Midpoint figures. The range on the right is what you should actually plan against.
Two things that change the number
VAT and CIL
VAT on a new build should be nil — but only if you handle it properly.
A VAT-registered contractor building a new dwelling zero-rates their own labour and the materials they supply, so it never appears on your invoice. Materials you buy yourself carry VAT at 20%, and you reclaim it under the DIY Housebuilders Scheme. The figures above are shown excluding VAT on that basis.
The deadline that catches people. For buildings completed on or after 5 December 2023 you have six months from completion to submit the DIY Housebuilders claim. Miss it and the money is simply gone. Keep every invoice from day one — you cannot reconstruct this later.
Community Infrastructure Levy. CIL can run to tens of thousands, and self-builders are exempt — but the exemption is procedural, not discretionary. Form 7 Part 1 must go in before permission is granted, a commencement notice must be filed before you start on site, and Part 2 follows completion. Miss a step and the full charge can land. No CIL is included in the figures above, because if you do it right there isn't any.
Be honest with yourself
What this does not include
Costs we have deliberately left out
Finance — mortgage arrangement fees (0.5–2% of the loan), interest during the build, stage-payment valuations at £150–£300 a visit
Living costs while you build — rent or a caravan for 12–24 months. On most first builds this is the single largest forgotten number
Furniture, blinds, curtains, appliances — and note appliances and carpets cannot be reclaimed under the DIY scheme
Section 106 or highways agreements — £2,000 to £15,000 for a new highway access, entirely site-specific
Party wall awards — £900–£1,500 per neighbour where they apply
Your own time — if you self-manage, that is a job. Cost it honestly before you choose the route
How these figures are built up
Build cost starts from a main-contractor rate for the specification you chose, adjusted for your build route and region. Rates are drawn from published UK cost data for 2026 and cross-checked against real tender returns. The range shown is −10% to +15% around the midpoint, which reflects how much genuine spread there is between competitive tenders on the same drawings.
Fees, external works, warranty, insurance and contingency are calculated from your build cost. Planning is £610 plus the £87.20 Planning Portal charge. Building Regulations is allowed at £2,000.
Reviewed August 2026. These rates move. If you are reading this more than a year later, treat them as indicative and ask us for the current version.
Total project, excluding VAT
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Plan against the top of this range, not the middle.
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Summary
Build cost—
Shape & complexity—
Energy & renewables—
External works—
Professional fees—
Statutory & surveys—
Warranty & insurance—
Contingency—
Plot & legal—
Midpoint—
Keep these numbers
Get the spreadsheet version and keep these numbers alive as the design firms up — it tracks what you actually spend against what you estimated.
We'll email your figures and the spreadsheet. Your details never go to a supplier.
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Saved. Your figures are on file. Here is the spreadsheet — it opens in Excel, Numbers or Google Sheets.
Self Build Mentor — independent guidance and mentoring only. We are not acting as your architect, engineer, contract administrator, project manager, principal designer or contractor, and this calculator is not a cost plan or a valuation. Figures are indicative, exclude VAT, and were reviewed in August 2026.
Sources: published UK build cost data 2026 · HMRC DIY Housebuilders Scheme · Planning Portal CIL guidance