Retrofit cost calculator (UK 2026)
A surveyor's working calculator for UK house retrofit cost in 2026. Compares heat-pump-only against phased deep retrofit, applies the BUS, ECO4, GBIS and 0% VAT grants, and reports payback at the Q3 2026 Ofgem cap.
The calculator
Live calculator
Q3 2026 cap baked inWhat this calculator does
It takes archetype, internal floor area, current and target EPC band, current annual gas spend, and grant eligibility, and returns four numbers: total capex (low to high), grant offset, net cost after grants, and payback years at the Q3 2026 Ofgem cap.
It does not pretend to replace a Retrofit Assessor (£400 to £800) or Coordinator (£1,500 to £3,500). It frames the conversation before those fees are spent.
Preset routes
Coefficients
Every coefficient is exposed on the sources manifest as a JSON object with the publishing URL beside it. The math is not proprietary; it is a transparent stack of published unit costs.