Adding a bathroom is the single biggest cost line in a basement finish, and the easiest place to blow the budget. Here’s the real breakdown.
The two scenarios
Plumbing was roughed in (best case): $12K–$22K
If your builder pre-roughed plumbing for a basement bath, you’re connecting fixtures and finishing. A standard 5×8 three-piece bath in Idaho Falls runs $12K–$18K with mid-range finishes, up to $22K for a 6×10 with tile shower.
No rough-in (cut concrete): $20K–$38K
Cutting and patching the basement slab for new plumbing adds $6K–$12K. Add a sewage ejector pump ($1,800–$3,500) if your bath sits below the main sewer line.
Line-item cost (mid-range basement bath, Idaho Falls, 2026)
- Plumbing rough-in and connections: $4,500–$8,000
- Toilet (mid-range): $400–$700 installed
- Vanity, top, faucet: $1,400–$3,200
- Tub or shower pan: $1,200–$2,800
- Shower wall tile + labor: $1,800–$4,500
- Floor tile + labor: $900–$2,200
- Exhaust fan (vented to exterior): $400–$700
- Lighting and mirrors: $400–$1,000
- Drywall, paint, baseboard: $1,200–$2,200
Where to save without regret
- Big-box vanity with a custom top: looks custom, costs half.
- Subway tile shower instead of imported stone slabs.
- Skip the rainhead, pick a pressure-balanced single function head you’ll actually love.
Where not to save
- Waterproofing membrane behind tile (Schluter or equivalent). Skip this and you’ll re-tile in 7 years.
- Exhaust fan sized to the room and vented all the way to outside.
- The valve. Cheap valves fail and force you into the wall.
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