Bathroom Plumbing Cost Calculator
Bathroom plumbing is priced by what moves. This separates a like-for-like swap from a layout change, because the gap between them is thousands.
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4 steps. What moves, the soil stack, extra fittings and region.
How this calculator works
Supply pipes can go almost anywhere. Waste cannot — it runs on gravity, so every WC, bath and shower needs a fall to the stack. That single fact explains most of the spread between a £900 bathroom and a £4,000 one.
Keeping the WC where it is, even if everything else moves, usually keeps you in the lower half of the range. Moving it means new waste at the right gradient, often notching or boxing joists, and sometimes relocating the stack itself.
On certification: the plumbing itself is not notifiable, but bathroom electrics are, under Part P. Ask which trade is certifying what, and get the paperwork.
The estimate hinges almost entirely on one answer: whether the WC, and therefore the soil stack, stays put. Keep it in place and you sit in the lower half of the range; move it and you are paying for new waste runs at the correct fall, joist work and often building control. That same gravity drainage is what makes a wet room conversion more involved than a standard refit. Timing matters too: second fix only happens once the walls are tiled, so it pays to line the plumber up around the tiling schedule rather than treat the two as separate jobs.
Bathroom plumbing cost by job (2026)
| Job | Typical 2026 cost | Notes |
|---|---|---|
| Plumbing first & second fix (full bathroom) | £900–£2,200 | Moving the soil stack is the big driver |
| Replace toilet, like for like | £150–£350 | Plus the unit |
| Replace shower valve or mixer | £150–£350 | Plus the valve |
| Waste re-route / new drain run | £200–£700 | Joist direction and available drop decide it |
| Move the soil stack | £800–£2,000+ | Structural; often needs building control |
| Plumber call-out / first hour | £60–£120 | London at the top of the range |
| Additional hourly rate | £45–£90 | Half-day and day rates often cheaper |
| Electrics, extractor & lighting | £450–£1,200 | Separate trade; notifiable under Part P |
Figures match our bathroom plumbing cost guide. Bathroom electrics are notifiable under Part P — ask who is certifying.
Bathroom plumbing calculator FAQs
Waste runs on gravity and needs a fall to the stack. Moving a WC means new waste runs at the right gradient, often notching joists, and sometimes relocating the stack — £800–£2,000+ against £150–£350 for a like-for-like swap.
First fix is the pipework buried before plastering. Second fix is hanging the taps, shower, WC and basin after tiling. A single quoted figure should still itemise both.
The plumbing itself is not, but bathroom electrics are notifiable under Part P, and any gas appliance work is legally Gas Safe. Ask who is certifying which part before work starts.
If it is lead, or plastic push-fit of unknown age, yes. It is far cheaper now than after the tiling is done, and it is the one decision people most often regret skipping.
Related cost guides
- Plumbing cost guide — every job priced
- Full bathroom costs — where plumbing sits in the total
- Bathroom repairs — when it is a fault, not a refit
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