Bay window replacement costs £1,250 to £3,000 for a fitted uPVC bay in 2026. The price turns on how many sections the bay has, its shape, and whether the old frames are holding up the wall above. Price yours in a minute, then get free quotes from local installers who will survey it.
What a new bay costs, fitted
These are fitted prices for a uPVC bay. The range is the one our calculator uses.
| Source | Fitted price, uPVC bay |
|---|---|
| Site benchmark (2026) | £1,250 to £3,000 |
| Checkatrade, three-section bay | £1,250 |
| MyJobQuote | £1,220 to £2,950 |
| FMB, smallest bay | £1,755 |
Sources as recorded in lib/research/knowledge-base-canonical.md. Timber and aluminium bays cost more.
Four things move a bay up the range: more sections, a curved shape, timber or aluminium frames, and any structural support the opening needs. Ask for that support as its own line, so two quotes can be compared.
What happens on the day
A bay is not one window. It is three or more frames joined at an angle, and in some houses the wall or the bay roof above rests on them.
- Props first.FENSA's guide says bays need temporary supports, such as Acrow props, during removal and installation.
- Loads checked. The GGF tells installers to work out the loads in the existing bay and specify bay poles to suit them.
- No load on the new frames. FENSA says most replacement window systems cannot carry load without extra support.
Bay, bow or a flat window
A bay projects in flat angled sections, usually three; a bow curves outward in four to six equal sections. If yours is curved, the Bow Window Cost Calculator prices it separately. Swapping a bay for a flat window changes how the house looks. The Planning Portal says windows of a similar appearance do not usually need permission and treats a new bay as an extension, so check with your council before you change the shape.
Replacing a 1930s bay
If your house is a 1930s semi, the 1930s bay window replacement cost page covers that job on its own.
Get free quotes for your bay
Tell us about the bay and we pass your details to local installers covering your area, who will contact you to arrange a survey.
Questions before you book
How much does bay window replacement cost?
A fitted uPVC bay costs £1,250 to £3,000 in 2026. Checkatrade prices a three-section bay at £1,250, MyJobQuote gives £1,220 to £2,950, and the FMB's smallest bay is £1,755. Bays with more sections, a curved shape or timber frames sit at the top of the range or above it.
Does a bay window need bay poles?
Only if the bay is carrying weight. The GGF's installation guide tells installers to work out the loads in the existing bay before removal and to specify bay poles to suit them. Most replacement window frames cannot carry load without extra support, according to FENSA, so the surveyor has to answer this before quoting.
Do I need planning permission to replace a bay window?
Usually not, if the new bay looks like the old one. The Planning Portal says new windows of a similar appearance to the house's do not usually need permission, but a new bay is treated as an extension. Listed buildings need consent, and conservation areas and Article 4 directions can add rules.