How we calculate window prices
Every price shown on this site is derived from a named data source. This page documents the full trail so you can audit it.
The pricing matrix
WindowCost maintains a public pricing matrix of 244 rows covering 61 UK towns × 4 material-and-glazing combinations (uPVC double, uPVC triple, aluminium double, timber double). Each row holds a low-to-high fully-fitted price range for a standard 1200×1000mm casement window and cites its source.
We chose the 1200×1000mm casement as the anchor unit because it is the most-quoted reference size across FENSA, Checkatrade, Which?, and major supplier brochures. Every other size (sash, bay, bifold, tilt-turn) is derived by a multiplier off this anchor.
Where the numbers come from
- Frame + glass unit cost: averaged across three UK supplier tiers — budget (Safestyle, QuickFitters), mid-market (Anglian, Everest), and premium (Residence Collection, Internorm). Updated quarterly against published trade-price lists and RRP where available.
- Installation labour: ONS regional labour indices (construction wages, skilled trades) applied as a percentage lift or discount against the national mean. London + South East labour runs ~20–40% above the national baseline; North East + Wales runs ~10–18% below.
- Regional adjustment factor: cross-checked against FENSA's published regional quote-average data (where public) and MoneySavingExpert's crowd-sourced installation cost threads.
- Heritage / conservation-area uplift: adjacent-town uplift factor applied when council open-data flags the postcode as Article 4 or Grade II+. Typically +15–40% on labour + material.
- Triple-glazing uplift (non-uPVC): where direct supplier data for aluminium and timber triple glazing is unavailable, we model as the double-glazed price × 1.30 (aluminium) or × 1.25 (timber), based on trade-interview data. This is clearly labelled as "modelled" in the calculator output.
Multipliers for window styles
Our calculator applies the following multipliers against the baseline casement price. These reflect relative installation complexity and unit cost, not arbitrary markups:
- Casement (standard) — ×1.00
- Tilt & Turn — ×1.15
- Sliding — ×1.10
- Sash (traditional box) — ×1.35
- Bay / Bow — ×1.60
Postcode-to-region mapping
UK postcode prefixes are mapped to the nearest town in our matrix using a hand-maintained lookup of the 128 standard UK postcode areas. When a postcode doesn't map to a direct-data town (e.g. PE → Peterborough), we use the nearest-labour-index equivalent town and flag the result as "modelled" in the output. We never silently substitute Birmingham baseline numbers without saying so.
What's not included in the headline price
- VAT reductions for ECO4, HUG2, GBIS, or Green Deal-eligible installs (covered separately in the grants section).
- Structural alterations (e.g. knocking out a bay to enlarge it, moving a lintel).
- Planning application fees in conservation or listed contexts — see our Article 4 guide.
- Scaffolding (adds £200–£900 per project for first-floor upward work).
Verification sources
The pricing matrix was last verified against published UK cost-guide data on
2026-04-21. Each row now carries a source attribute
and a verified date in pricing-matrix.json.
| Source | Used for |
|---|---|
| Checkatrade cost guides | Captured 2025-04 |
| HomeOwners Alliance double glazing guide | Ongoing reference |
| MoneySavingExpert double glazing community threads | Ongoing reference |
| ONS regional labour cost indices 2025 Q4 | Ongoing reference |
| FENSA published regional quote averages | Ongoing reference |
UK baseline anchors (1200×1000mm casement, fully fitted)
| Spec | Low | High | Avg |
|---|---|---|---|
| uPVC · Double | £500 | £1250 | £875 |
| uPVC · Triple | £750 | £1750 | £1250 |
| Aluminium · Double | £900 | £2200 | £1550 |
| Timber · Double | £1200 | £3500 | £2350 |
Regional factors (applied against UK baseline)
| Region | Factor |
|---|---|
| London | ×1.3 |
| South East | ×1.2 |
| South West | ×1.05 |
| Midlands | ×1 |
| North | ×0.85 |
| Scotland | ×0.88 |
| Wales | ×0.85 |
| Northern Ireland | ×0.82 |
How often we refresh
Our target is a quarterly review cycle of the pricing matrix. First cycle kicks off Q3 2026 once the site has a meaningful traffic baseline and we have three UK supplier-quote touchpoints per material × glazing class to verify against. Until then, numbers are the initial derivation documented above, last computed 2026-04-21.
Material changes to a row are logged in the public git history of this repository, and the
updated: frontmatter on the corresponding guide will reflect the real edit date.
How to report a correction
If you've just had a quote that deviates materially from our published range, we want to know. Send the quote number, postcode, material, and date to info@saasquatch.co.uk. We credit every verified correction on the methodology change log.
This methodology is maintained publicly. The pricing-matrix file and every edit to it is visible in our GitHub repository at github.com/MidknightZERO/windowcost.