Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Applies a regional labor-and-bid multiplier to the whole job.
Result
Cost to add the bathroom
$16,997
Base bathroom build
$12,500
Plumbing run to the stack
$2,280
Slab cutting and repour
$0
Fixture and finish upgrade
$0
Contingency reserve
$2,217
Share of hard cost that is plumbing distance
15.4%
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter bathroom type.
- 2Enter region — Applies a regional labor-and-bid multiplier to the whole job..
- 3Enter distance from existing drain stack (ft).
- 4Enter drain and supply run cost ($/ft).
- 5Enter floor construction.
- 6Enter framing new walls / stealing closet space ($).
- 7Enter fixture and finish grade.
- 8Enter contingency (%).
- 9Read your cost to add the bathroom on the right — it updates as you type.
- 10Hit Share to keep the scenario or send it to someone.
About this calculator
Adding a bathroom is a plumbing project wearing a tile costume. The fixtures are the visible cost and rarely the deciding one — what moves the number is how far the new drain sits from the existing stack, whether the floor is a slab that has to be cut and repoured, and whether the space already exists or has to be framed out of a closet or a corner of a bedroom. This calculator prices those separately so you can see the trade: moving a half bath ten feet closer to the stack often saves more than downgrading every fixture. Worked assumption for the defaults: a full bath in existing space, 12 ft from the stack, mid-grade fixtures, wood-framed floor, ventilation and electrical included, 15% contingency — about $17,000 nationally and about $23,500 in a West Coast metro.
Worked example
Using the values the calculator loads with:
Inputs
- Bathroom type: Full bath with tub/shower — $12,500 base
- Region: US national average — 1.00×
- Distance from existing drain stack: 12 ft
- Drain and supply run cost: 190 $/ft
- Floor construction: Wood-framed floor — no slab work
- Framing new walls / stealing closet space: 0 $
- Fixture and finish grade: Mid-grade — included in base
- Contingency: 15 %
Results
- Cost to add the bathroom: $16,997
- Base bathroom build: $12,500
- Plumbing run to the stack: $2,280
- Slab cutting and repour: $0
- Fixture and finish upgrade: $0
- Contingency reserve: $2,217
- Share of hard cost that is plumbing distance: 15.4%
What each field means
Inputs
- Bathroom type
- Pick the option that matches your situation — the maths changes per option. Choices: Half bath (toilet + sink) — $7,500 base, Full bath with tub/shower — $12,500 base, Primary bath with double vanity and walk-in shower — $19,000 base.
- Region
- Applies a regional labor-and-bid multiplier to the whole job.
- Distance from existing drain stack (ft)
- The distance from existing drain stack used in the calculation, measured in ft. Starts at 12 ft so you have a working example on load. Accepted range: 0–120 ft.
- Drain and supply run cost ($/ft)
- The drain and supply run cost used in the calculation, measured in $/ft. Starts at 190 $/ft so you have a working example on load. Accepted range: 60–600 $/ft.
- Floor construction
- Pick the option that matches your situation — the maths changes per option. Choices: Wood-framed floor — no slab work, Concrete slab — cut, trench and repour: $3,800.
- Framing new walls / stealing closet space ($)
- The framing new walls / stealing closet space used in the calculation, measured in $. Starts at 0 $ so you have a working example on load. Accepted range: 0–40000 $.
- Fixture and finish grade
- Pick the option that matches your situation — the maths changes per option. Choices: Mid-grade — included in base, Upgraded tile and fixtures — +$4,200, High-end (stone, custom glass, heated floor) — +$11,000.
- Contingency (%)
- The contingency used in the calculation, measured in %. Starts at 15 % so you have a working example on load. Accepted range: 0–35 %.
Results
- Cost to add the bathroom
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Base bathroom build
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Plumbing run to the stack
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Slab cutting and repour
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Fixture and finish upgrade
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Contingency reserve
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Share of hard cost that is plumbing distance
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Why does distance from the stack matter so much?
Drain lines need continuous fall — about a quarter inch per foot — plus venting. Long runs mean opening more floor, more joist drilling or a new vent through the roof, and sometimes a pump if gravity will not cooperate.
Does adding a bathroom raise my home value?
Usually, especially going from one bathroom to two, though recovery at resale is typically partial rather than full. The stronger argument is livability; treat value recovery as a bonus.
Is a macerating toilet cheaper than a proper drain?
Up front, often yes — it avoids slab cutting. Long term you own a pump that can fail and some buyers discount it. Price both paths before deciding.
Where does the regional multiplier come from?
It is a job-level index against a US national average of 1.00, built from the spread contractors quote between low-cost rural markets and the highest-cost coastal metros. Materials vary less than labor, but bids move together, so one index tracks real quotes better than splitting them. Swap in your own multiplier by picking the tier closest to two bids you already have.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Cost to Add a Bathroom Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/cost-to-add-a-bathroom-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/cost-to-add-a-bathroom-calculator" target="_blank" rel="noopener">Cost to Add a Bathroom Calculator — RevenueLab</a> (2026).</p>
Source: [Cost to Add a Bathroom Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/cost-to-add-a-bathroom-calculator) (2026).