What this site is, and is not
Double Glazing Cost Calculator is an aggregator and reviewer of published double glazing cost data. We read the major 2026 UK cost guides, compare what they say, reconcile the differences and present a single honest consensus range for each figure. We are clear about what we are not: we are not a primary research operation, we have not physically collected a set of installer quotes ourselves, and we do not claim a proprietary survey. Earlier drafts of this site referred to a "54-quote survey". That claim has been removed because we did not run one, and putting a number on research we did not do would be exactly the kind of overclaiming we warn readers about elsewhere.
The sources we use
For every price we cross-check at least two independent sources, and usually more. Our core 2026 sources are Checkatrade, the Federation of Master Builders (FMB), GreenMatch, ExpertSure and StayWarm, supplemented by installer cost guides such as whatcost, idlwindows and lotuswindows. Checkatrade gives us per-window fitted ranges and labour rates, the FMB gives a full-set price for a typical three-bedroom home, GreenMatch and whatcost anchor the whole-house ranges, and ExpertSure is our reference for the 2026 grant changes. No source is used in isolation, and no installer pays to be cited.
How we turn sources into a figure
Published guides rarely agree on an exact price, so we do not pretend they do. For each line, such as a fitted uPVC casement, we gather the ranges from every source, trim obvious outliers (for example a single very high bay-window figure that sits far above the rest), and state a low, average and high. Where the sources genuinely diverge we show the spread rather than hiding it behind one tidy number. The result is the set of ranges you see in our costs hub and behind every calculator. Each calculator multiplies a per-window range by your inputs, so its output is always a range, not a false-precision single figure.
An example: cost per window
Take the headline figure of about £650 fitted for a uPVC casement. Checkatrade puts it at £500 to £1,250, StayWarm at a typical £450 to £1,200, and idlwindows lower at £300 to £600. Rather than pick the prettiest of those, we publish a consensus of £400 to £1,000 with a £650 average, which is the basis for our cost-per-window guide. The same approach gives the £4,000 to £10,000 range for an average semi: it reconciles the FMB's roughly £4,130 full set, GreenMatch's £4,000 to £16,500 and Checkatrade's premium £8,000 to £15,000, using realistic window counts of eight to twelve rather than an inflated number.
Who writes this
Everything on this site is written by Tom Bradley, a FENSA-registered installer with over 20 years fitting windows. The figures are not just scraped from the web: they are checked against what the work actually costs on a real job, then cross-referenced with the published 2026 cost guides. If a price looks wrong against the day-rate reality of fitting, it does not go on the site.
I check every figure on here against what a job really costs to do. I have fitted enough windows to know when a number is fantasy. If it would not stand up on a real install, it does not get published.
Tom Bradley, FENSA-registered installer
What we do not claim
We do not claim to be cheaper than your local installer, because we do not sell anything. We do not promise a specific saving on your bill: the Energy Saving Trust figure of up to around £140 a year is presented as an "up to", because it varies with house size, region and your current windows. We do not guarantee grant funding, because only around 15% of households qualify, and we never say "free double glazing" without the eligibility caveat, as set out in our grants guide. And we do not invent figures: if a number cannot be traced to a named source, it does not appear on the site.
How often we update
Window prices and grant rules move, so the data here is dated. The figures on this site were last verified in 2026 against the sources above, and every article shows the date it was last reviewed. We refresh the ranges when the major cost guides publish new editions, and we update the grants content promptly when a scheme opens or closes, as happened when ECO4 closed to new applications on 31 March 2026. If you spot a figure that no longer matches a current published source, it is due an update.
Use the figures the right way
Everything here is a guide range to help you judge a quote, not a quote itself. Run the uPVC window calculator for a realistic starting figure, then get at least three written quotes and compare like for like. If a price comes in well above our ranges, read how to avoid being overcharged before you sign anything.