2026 Projection-window planner
Estimate the installed cost to replace a traditional three-panel bay window, with a center window and two angled side windows. The calculator adjusts for frame, glass, installation scope, access, repairs, extras, and local market.
Bay window prices are highest when the proposal includes support, roof or head flashing, an insulated seat, exterior cladding, interior trim, and repair work. Keep those lines visible before comparing totals.
For an 8-foot bay window cost, use one unit in the calculator and keep the 30° or 45° projection angle, center-to-side panel proportions, support, flashing, seat insulation, and interior trim visible as separate cost drivers. Pricing a curved 4–6 panel assembly? Use the Bow Window Cost Calculator.
Estimate one three-panel bay replacement
Actual bid intake
Enter the quote total, three-panel bay structure, included scope, access, and optional line items to see whether the bid looks low, fair, or high against the same planning model.
Bay quote checker
Use the same bay/bow planning basis as the calculator, then add width, projection, panel layout, support, flashing, seat, trim, repair, and access details from the contractor quote.
Contractor quote readout
Enter quote total, quantity, bay width, projection/depth, panel count, and scope details, then run Check quote.
Quick planning range
A replacement unit is only part of the job. A useful quote identifies the projection, support, roof or head flashing, insulated seat, exterior finish, interior trim, and repairs around the opening.
| Frame | Installed range | What still varies |
|---|---|---|
| Vinyl bay | $3,554–$10,245 | Size, angle, center/side configuration, glass, finishes, support, and opening condition |
| Wood bay | $3,461–$12,452 | Species or cladding, finish work, custom sizing, glass, and installation scope |
Source range: Home Depot Window Installation Cost Guide. These are broad planning ranges, not quotes.
Where the quote changes
Bay windows commonly use three sections with a wider center view and two angled side windows. Width, 30° or 45° angle, center-to-side proportions, operating sashes, roof geometry, and custom glass change product and handling cost. Bow windows use a separate 4–6 panel curved model.
Cables, header attachment, knee braces, and the condition of the framing determine how the projecting assembly is carried.
Head flashing, roof details, exterior cladding, sealant joints, and drainage must work together around the projection.
The insulated seat, casing, stool, apron, wall repair, paint, and nearby flooring can be separate or included line items.
Use the window replacement calculator for the rest of the house, then keep the three-panel bay projection as its own scenario so the average does not blur structural work.
Quote comparison
Bay-window prices are difficult to compare when one proposal lists only the unit and another includes structural, flashing, roofing, insulation, trim, disposal, and repair work. Ask each bidder to separate the window assembly from opening preparation and finish work.
Before signing
Plain answers
The site's published planning ranges are approximately $3,554 to $10,245 for a professionally installed vinyl bay window and $3,461 to $12,452 for wood. Size, projection angle, center-to-side panel proportion, glass, roof and seat construction, structural support, trim, access, and opening condition can move a quote outside those ranges.
A bay window projects beyond the wall with a center window and two angled side windows. Replacement may involve a roof or head flashing, an insulated seat, cable or knee-brace support, exterior cladding, interior finish work, and correction of water damage around the opening.
Often it can, but the installer still needs to verify the rough opening, support, water management, insulation, and surrounding finishes. Changing a flat window into a bay or resizing the opening is a different and usually more expensive scope than replacing an existing projection unit.
Ask for dimensions, projection, window styles, frame and glass package, structural support, roof or head flashing, seat insulation, exterior cladding, interior trim, disposal, permits, repair allowances, and separate product and labor warranties.