Window Replacement Cost in O'Fallon: What Moves the Price
Typical Ranges for the St. Louis Area
| What | Typical range | Source |
|---|---|---|
| Whole window replacement project | $3,108 to $9,479 (average $6,278) | Angi, St. Louis, July 2026 |
| Per window | $300 to $1,500 | Angi, St. Louis, July 2026 |
| Vinyl frame, per window | $100 to $900 | Angi, St. Louis, July 2026 |
| Bay window | $900 to $7,100 | Angi, St. Louis, July 2026 |
| Patio door replacement | $1,550 to $6,250 (average $2,500) | Angi, national, October 2026 |
| Basement window, per window | $400 to $1,000 (average $700) | Angi, national, October 2026 |
These are typical ranges from published cost data, not a quote. Your estimate is based on your actual windows.
What Changes the Price
- How many windows. More windows in one job usually lowers the price per window.
- Size and style. Large, custom and specialty windows like casements, bays and bows cost more than a standard double-hung.
- Frame material. Vinyl costs the least; fiberglass and wood cost more.
- Glass. Triple pane, low-E coatings, gas fill and tempered glass add cost.
- Installation method. Full-frame costs more than insert, because more comes out and more goes back in.
- Hidden damage. Rot in a frame, sill or wall shows up once the old window is out. We tell you about it before fixing it.
- Access. Second-story and hard-to-reach windows take more time.
A Few Windows Now or the Whole House
Replacing every window in one job spreads the cost of measuring, ordering and setting up across more windows, so the price per window tends to drop. It's also one disruption instead of several. Replacing in stages works too: start with the windows in the worst shape and do the rest when the budget allows. Either way, ask for the per-window price on your estimate so you can compare.
What a Written Estimate Should Include
- The number of windows and the size and style of each
- The manufacturer and product line
- Frame material, glass package and color
- Insert or full-frame installation, opening by opening
- Interior and exterior trim work
- Removal and disposal of the old windows
- What happens if rot or damage turns up, and how it's priced
- Warranty terms in writing, for the product and the installation
If an estimate leaves any of these out, ask before you sign.
Window Replacement Cost Questions
What is the average cost of replacing 10 windows in a house?
Using Angi's St. Louis range of $300 to $1,500 per window, ten windows would land somewhere between $3,000 and $15,000. Where yours land depends on the windows: ten standard vinyl double-hungs sit near the low end, and a mix with a bay or large picture windows pushes it up.
Why are new windows so expensive?
Each replacement window is built to the size of your opening, with a sealed insulated glass unit, and installed by hand with flashing, insulation and trim. Labor is a big share of the cost. Specialty glass, custom sizes and repairs to the opening add more.
How can I get windows replaced for less?
Choose vinyl, stick with standard styles, skip upgrades you don't need, and replace more windows at once if you can. Insert installation costs less when your frames are sound. A detailed written estimate shows you which line items you can trim.
What are the best replacement windows for the money?
For most houses, a well-built vinyl window with double-pane low-E glass. It costs less than fiberglass or wood and performs well. Spend more where it counts: on the installation, on full-frame work where the frames need it, and on triple-pane glass only where noise calls for it.