Cost guide
Bathroom Addition Cost in 2026
A new bathroom needs plumbing, a vent, a waterproof finish and its own share of the addition fixed costs. Size matters less than what goes in it.
Step 1 of 4
Your addition
Size and type.
Labor costs differ a lot by state. This adjusts every line.
New finished floor area, not counting the existing house.
Type of addition
Foundation
Estimated addition cost
$113,900
$73,000 – $154,800
The calculator above starts as a room without a bathroom. Open it set to a 100 sq ft bathroom addition to price your own.
Bathroom addition cost by size and type
| Scenario | Estimated range | Per sq ft |
|---|---|---|
| Bump-out bathroom (80 sq ft)Small extension off an existing wall, full bath | $39,200 – $98,800 | $490–$1,235 |
| Small full bath (100 sq ft)Ground floor, slab foundation, standard finishes | $44,900 – $112,800 | $449–$1,128 |
| Larger full bath (150 sq ft)Room for a separate tub and shower | $55,200 – $132,300 | $368–$882 |
| Bathroom on a second story (100 sq ft)Built over the existing house | $46,200 – $111,000 | $462–$1,110 |
Estimates at national-average pricing, calculated with our own pricing engine and reviewed September 2026. Change the inputs in the calculator to price your exact project.
A 100 sq ft full bathroom on the ground floor costs about $44,900–$112,800. The per-square-foot figure looks high because the bathroom fixtures, plumbing, design fees and permits are spread over very few square feet.
What drives bathroom addition cost
- Type matters most: a second story costs more per sq ft than a ground-floor room, but needs no new foundation.
- Bathrooms and kitchens are plumbing-heavy and can add $30k–$70k.
- Architect fees, permits and utility tie-ins are often missing from rough quotes.
- Additions carry more unknowns, so this estimate includes a larger contingency.
Ways to keep a bathroom addition affordable
- Put the new bathroom next to existing plumbing walls to shorten supply and drain runs.
- Consider converting an existing closet, hallway or bedroom corner. It avoids the shell and foundation entirely.
- Pick standard fixtures and prefab or simple tile for the shower. Custom stone and glass add the most.
- Ask for itemized quotes so you can compare the plumbing, tile and electrical lines.
Frequently asked questions
How much does it cost to add a bathroom?
A 100 sq ft full bathroom addition on the ground floor costs about $44,900–$112,800. The range depends on your state, fixtures, tile and whether the plumbing is close by.
Is it cheaper to add a bathroom inside the house?
Yes. Converting existing space skips the foundation, framing and roof, so you pay mostly for plumbing, waterproofing, finishes and permits. Use the bathroom remodel calculator to price it.
What does a bathroom cost inside an addition?
The fixtures and finishes for a full bathroom run about $12,000 to $30,000 before contingency, on top of the cost of the space itself.
Do I need a permit to add a bathroom?
Almost always. New plumbing, electrical and ventilation need permits and inspections in most cities.