LIVE · Q4 2025 BUILD COST DATA

Know what your project really costs to build.
In 45 seconds.

Based on quarterly-updated per-m² averages from public build cost records and 2,000+ completed Arkiplan projects, adjusted for your postcode and finish level. No forms, no sales call — just a realistic range you can plan around.

2,000+projects
in dataset
±8%Accuracy vs.
builder's quote
45sAvg. time
to answer
Latest benchmark · 30m² extension · SW11 £92,400 – £118,600

How we calculate this

Our estimate isn't a guess. It's public data plus 2,000 real builds.

01 · BENCHMARK

Per-m² benchmarks, updated quarterly.

Our figures are based on quarterly-updated per-m² averages drawn from public build cost records and our own completed projects — so you're looking at what real extensions, lofts and renovations are actually costing right now, not last decade's numbers.

02 · REGION

Regional multipliers.

Building the same extension in Fulham vs. Cardiff isn't the same. We apply a regional adjustment from your postcode — typically ±28% either side of the UK average.

03 · FINISH

Finish level accounted for.

"Standard" vs. "Premium" vs. "Luxury" changes the figure dramatically. Kitchen and bathroom spec alone can move a 30 m² extension by £25k.