The hidden costs of double glazing
The headline per-window price is written to win the quote; the real cost is what you pay once fitting, removal and making good are counted. Here is what the sticker leaves out — and how to compare on the true total.
What the sticker leaves out
Some quotes price the units alone and leave installation out, so a cheap per-window figure can exclude the fitters' day rate entirely. Confirm whether the price is supply-only or supply-and-fit before comparing two quotes.
Taking out the existing frames and glass and disposing of them properly is labour and waste cost that is often folded in silently — or, on a bare supply quote, left for you to arrange.
New frames rarely sit perfectly into old openings. Re-plastering internal reveals, re-pointing or sealing outside, and repainting are frequently billed on top as 'making good' once the units are in.
Upper-floor or awkward-to-reach windows can need scaffolding or a tower for safe access, and that access cost is typically separate from the per-window price.
Replacement windows usually have to meet current building regulations, which can mean trickle vents, safety glass in certain locations, and a compliance certificate — each a real cost that a bare unit price ignores.
A technical survey, cills, add-on trims, and any repair to rotten timber or lintels found once the old window is out are extras that surface after the headline quote.
Why the per-window price misleads
A double-glazing quote fixes the price of the units, and that figure is real — but fitting, removing and disposing of the old windows, making good the reveals, access and certification are the costs that actually make the job expensive, and they sit alongside it. Because one installer bundles making good and another leaves it out, comparing on the per-window price alone is unreliable — a 'cheap' quote can carry a large hidden commitment once every stage of the work is counted. The true total is the only number that compares like with like.
How to work out your true total
Start from the price of the units for your window count, then add fitting if it is a supply-only quote, removal and disposal of the old frames, making good to the reveals inside and out, any scaffolding or access, trickle vents and the compliance certificate, plus a realistic allowance for repairs found once a window is out. For a sourced, dated figure on specific options — each line graded by how well we can verify it — run it through the calculator rather than relying on a rule of thumb.
How we stay honest about this
If you buy through a partner link we may earn a referral fee at no extra cost to you, and it never changes which option we rank first or the figures we show. Placement can't be bought — the order is decided by the true total and verifiable quality, never by who pays us. See our affiliate disclosure and methodology.
Rules of thumb only get you so far. Run a specific option through the calculator for a sourced, dated, confidence-graded figure.
Frequently asked
Not always — some quotes are supply-only, pricing the units alone and leaving installation, removal of the old windows and making good for you to arrange or pay for separately. Always confirm whether a quote is supply-only or supply-and-fit before comparing it with another.
It is the finishing work once the units are in — re-plastering the internal reveals, sealing and re-pointing outside, and repainting. It is frequently billed on top of the window price, so fold it into your comparison rather than assuming the opening is left ready to decorate.
Replacement windows usually have to meet current building regulations, which can require trickle vents and safety glass in certain positions, plus a compliance certificate. It is a genuine cost that a bare per-window price leaves out, so treat it as a real line in the total.
Related guides
See the big picture in the Hidden-Fee Index — how much the advertised price hides across every category — or browse all buyer guides.
This guide explains typical, well-known cost mechanisms for general education — actual fees vary by operator, destination and date. Confirm live prices, fees and your consumer rights with the retailer and official sources before you buy. TrueTotal provides guidance, not financial or legal advice.