Bay vs bow window cost calculator
Bay and bow windows are a project, not a swap: this tool totals your unit price, labor and add-ons with a contingency buffer, and holds the result against the labeled installed band.
A bay/bow unit at $2,500.00 plus labor is about $3,630.00 (labeled band $1,500.00–$4,500.00 installed). Bay (3 angled units) and bow (4–5 gently curved units) project out and often need a structural sill/head and exterior finish — that carpentry and any header are a pro/structural item, not sized here.
Calculator inputs
A bay (three angled units) or bow (four to five gently curved units) window projects out from the wall, so it costs far more than a flat replacement of the same width — the labeled band runs $1,500–4,500 installed. The unit itself is only part of it: the projection usually needs a structural sill and head board, a roof or seat build-out, and exterior finish, and that carpentry is where budgets slip. This tool totals your quoted unit price, labor and any add-ons, then adds a contingency buffer.
Enter the prices from your own quotes; the labeled band is a sanity guide, not a price you should expect. The structural sill/head and any header are a pro/structural item and are not engineered here.
Formula
Subtotal, then a contingency buffer:
total = (count × price + labor + add-ons) × (1 + contingency)
The contingency (10% by default, your call) covers the surprises a projecting window tends to produce — rot at the old opening, an out-of-square wall, a re-flash.
Worked example
One bay unit at $2,500, $800 labor, no add-ons, 10% contingency:
- Subtotal: (1 × $2,500) + $800 = $3,300
- Contingency: $3,300 × 10% = $330
- Total: $3,300 × 1.10 = $3,630
That $3,630 sits inside the labeled $1,500–4,500 band — reasonable for a modest bay. A larger unit needing a built-out roof, seat and full exterior finish would push the add-ons up and land near the top of the band or beyond.
Background & practice
Budget the carpentry, not just the glass. The single most common reason a bay/bow quote comes in high is the projection work: a cantilevered seat or a small roof, flashing, soffit and matching exterior finish. Put those in the add-ons field explicitly so your total is honest. A structural header for the wider opening, if the wall is load-bearing, is a separate engineered item — defer it to a structural pro.
What to confirm. Whether the existing opening is being widened (permit and structural work likely — see the timeline & permit reference), and whether the quote includes interior trim and the seat board. Get the itemized breakdown in writing.
Common mistake. Treating a bay/bow like a same-size unit swap. It is closer to a small addition, and the labor and finish often rival the cost of the window itself.
Reference table
| Window type | Typical installed band ($/window) | Character |
|---|---|---|
| Double-hung | $300.00–$800.00/window | Two vertical sashes; the value default |
| Casement | $400.00–$1,000.00/window | Crank-out; seals tight, opens fully for egress |
| Sliding | $350.00–$900.00/window | Horizontal glider; value option |
| Awning | $400.00–$1,000.00/window | Top-hinged; vents in rain |
| Picture | $300.00–$1,200.00/window | Fixed; best U-factor, no ventilation |
| Bay / bow | $1,500.00–$4,500.00/unit | Projecting multi-panel unit |
Installed (material + labor) planning bands, not a quote — you enter the real per-window price above.