The formula
For each line item we multiply a quantity by a national unit cost, then apply a quality-grade factor. A regional labour multiplier is applied to the labour portion only; materials are priced nationally. We show the itemised result as a ±20% range.
National unit costs
| Line item | National unit cost | Source |
|---|---|---|
| Old window removal | £105.00 / m² | checkatrade.com (source for Old window removal) |
| Window unit | £470.00 / m² | checkatrade.com (source for Window unit) |
| Installation labour | £265.00 / m² | checkatrade.com (source for Installation labour) |
| Trim, flashing & finish | £88.00 / m² | checkatrade.com (source for Trim, flashing & finish) |
| Disposal | £30.00 / m² | checkatrade.com (source for Disposal) |
Regional labour multipliers
Each region's labour multiplier is its mean construction-trades wage relative to the GB mean, from ONS ASHE Table 15 (SOC 531, Construction and Building Trades; 2024 revised edition) — a broader occupation than a window-fitter-specific series because ONS suppresses narrow-occupation regional wage data, the same proxy basis used by the GB roof calculator. Multipliers are bounded to a sane range and applied to the labour share of each line item, so materials stay nationally priced while labour tracks local wages.
Data vintage and limitations
Compiled June 2026 from public cost aggregators and government wage data. These are derived estimates, not live contractor quotes. Local prices vary with project complexity, access, and material availability; always confirm with a licensed contractor before budgeting.
Tax and data notes
- VAT
- The calculator applies the configured standard UK VAT rate of 20% to its renovation estimate and shows the VAT-inclusive total. Some projects or properties can qualify for different treatment, so confirm the rate and any exemptions on each contractor quote.
- How firm these costs are
- The national renovation model is assembled from the public cost guides cited for its individual inputs, then calibrated against a cited market range. Individual line prices are planning allocations rather than live quotes; compare the result with itemised quotes from qualified contractors before budgeting.