Project Cost Calculator

Domestic Project Cost Calculator — Pentangle Design
Budget guide · Extensions & new homes

What might your project cost?

Toying with an extension, or a new house from scratch, and trying to work out whether the numbers stack up? This calculator gives you a ballpark — a sensible starting figure to test an idea against, before anyone reaches for a tape measure.

Pop in your floor areas, choose a finish and a location, and tell it how awkward the site is. You’ll get a budget range built on current UK construction costs. It takes about a minute.

Feasibility Cost Plan · Order of Magnitude

Project Cost
Calculator

PENTANGLE DESIGN LTD
Basis: £/m² GIFA, ex VAT
Rates effective: —
01 Project & Measurement
m²
m²
m²
Lightredecorate +
Moderatestrip & refit
Fullgut & rebuild
Single1 storey
Two2 storeys
Three+3 storeys
02 Specification & Site
Lowbuilder std
Midgood quality
High endbespoke
1 simple510 severe
Straightforward — reasonable access, no major abnormals.
03 Fit-out hotspots
New kitchensupply & fit, at chosen finish
Utility roomunits, plumbing, worktop
Bathrooms / en-suitesfull supply & fit, each
0
04 Overlays
Demolitionclearance of existing structures
m²
External worksdrives, patios, drainage, landscaping
8%
Contingencydesign + construction risk
10%
Professional feesarchitect, engineer, consultants
12%
Cost Plan OutputEXTENSION
Proposed area cannot be less than existing area.
Construction cost — central estimate
£0
Effective rate £0/m²
excludes VAT
LowerCost-certainty bandUpper
£0£0
New-build floor 0 m² @ £0 £0
Remodelled floor 0 m² @ £0 £0
Demolition 0 m² £0
External works 8% £0
Fit-out kitchen, 1 bath £0
Works subtotal £0
Contingency 10% £0
Professional fees 12% £0
VAT @ 20% £0
Total inc VAT £0

Excludes

Land & acquisition · FF&E & loose furniture · planning/BR fees & CIL · finance & legal · abnormals beyond the complexity allowance (contamination, piling, service diversions, party-wall awards).

Status & confidence Feasibility-stage benchmark only. Rates derive from current UK market data and are sound as order-of-magnitude figures — confidence is good on the bands, lower on any single output, because real cost is driven by site specifics, procurement route and tender conditions. It does not replace a measured estimate, bill of quantities or competitive tender. Treat the band, not the central figure, as the answer.
Disclaimer. This calculator provides indicative guidance only and does not constitute a quotation, estimate, or professional advice on which any reliance should be placed. Figures exclude VAT unless shown. No liability is accepted for decisions taken on the basis of these outputs. For a costed proposal tailored to your project, please get in touch.

What this is — and what it isn’t

This is a budgeting tool, not a quote. Every project is a one-off: ground conditions, access, the design itself and the state of the market on the day all push the real figure around — sometimes by a lot. Treat the result as an order-of-magnitude guide for deciding whether an idea is worth pursuing, and lean on the range rather than the single number.

A firm, costed figure comes later — from drawings, a proper specification and a builder’s tender, not from a website. The calculator also sets aside land, finance, statutory fees and the genuinely unpredictable: contamination, awkward foundations, the surprises no spreadsheet sees coming. In short: useful for a first sniff of viability, not for signing anything.