Invoicing for Plumbers: UK Guide to Getting Paid Faster

You finish a boiler install at 4pm on a Friday. The customer wants an invoice. You could send one now — but the spreadsheet is on your laptop at home, and you need to check the materials costs from the merchant receipts in the van. So the invoice goes out next Wednesday. Or the Wednesday after that.

Late invoices are the most common cash flow problem for UK plumbing businesses, and the fix isn't "be more disciplined." It's having an invoicing process that doesn't require you to re-type everything from scratch.

What a Plumber's Invoice Must Include

Every UK invoice needs these basics. Skip any of them and you risk delayed payment or tax compliance issues.

Standard invoice requirements:

• Your business name, address, and contact details
• Customer name and site address
• Unique invoice number (sequential — INV-001, INV-002, etc.)
• Date of issue
• Description of work completed
• Itemised breakdown: labour, materials, and any other charges
• Payment terms (e.g., "Due within 14 days")
• Payment methods accepted
• Total amount due

If you're VAT-registered, also include:

• Your VAT registration number
• VAT rate applied to each line item (standard 20%, reduced 5%, or zero-rated)
• VAT amount
• Gross total (including VAT)

If CIS applies (subcontracting for a contractor), include in practice:

• Your Unique Taxpayer Reference (UTR) — the contractor needs this to verify your CIS status
• CIS deduction rate (20% registered, 30% unregistered, 0% gross payment status)
• CIS deduction amount
• Net payment after deduction

VAT for Plumbing Work

The current UK VAT registration threshold is £90,000. If your taxable turnover over the last 12 months exceeds this, you must register for VAT.

Once registered, VAT applies to your services at different rates depending on the work:

Work Type	VAT Rate	Example
Standard plumbing services	20%	Boiler repair, leak fix, bathroom installation
Energy-saving materials installation	5%	Solar thermal, heat pump installation, insulation
New-build construction	0%	First-fix and second-fix plumbing on a new build
Work for disabled persons	0%	Adaptations to bathrooms for disability access

Materials vs labour: VAT applies to both materials and labour on most jobs. You charge VAT on the full invoice amount (labour + materials), not just the labour.

Domestic reverse charge: If you're VAT-registered and subcontracting for a CIS-registered contractor, the domestic reverse charge may apply. Under reverse charge, you don't charge VAT on your invoice — the contractor accounts for the VAT on their own return. This rule (in effect since March 2021) applies when all three conditions are met: both parties are VAT-registered, the work is standard-rated or reduced-rated construction services, and the contractor has not provided written end-user notification. Check whether the reverse charge applies before invoicing — the wrong VAT treatment creates problems for both parties.

CIS for Plumbing Subcontractors

If you do subcontracting work for a CIS-registered contractor, CIS deductions apply to the labour portion of your invoice. Materials, VAT, equipment hire, and consumables are excluded from the deduction calculation.

Example: You invoice a contractor for second-fix plumbing on a house extension:

Item	Amount
Labour (3 days at £350/day + apprentice 3 days at £120/day)	£1,410
Materials (copper pipe, fittings, sanitaryware)	£1,850
Waste disposal	£90
VAT (reverse charge — not invoiced)	£0
Gross total	£3,350

CIS at 20% on labour: £1,410 × 20% = £282

Net payment received: £3,350 − £282 = £3,068

The £282 goes to HMRC as an advance payment against your annual tax bill. You claim it back when you file your Self Assessment or Corporation Tax return. See our full CIS payments guide for details on registration, gross payment status, and April 2026 changes.

Handling Materials on Invoices

Plumbing jobs are materials-heavy. A bathroom install can easily be 50-60% materials by cost. How you handle materials on your invoice affects both your margin and your CIS deductions.

Option 1: Buy materials, invoice at cost plus markup. You buy materials from the merchant, add a markup (10-20% is common for plumbing), and invoice the customer for the marked-up amount. The markup covers your time selecting, collecting, and transporting materials. This is the most common approach for direct customer work.

Option 2: Invoice materials at cost, increase labour rate. Some plumbers prefer to pass materials through at cost and build the margin into their day rate instead. Simpler invoicing, but less transparent on where the margin sits.

Option 3: Customer supplies materials. The customer buys their own fixtures and fittings. You invoice labour only. Clean from an invoicing perspective, but you lose the materials markup and carry the risk of unsuitable materials arriving on site.

Whichever approach you use, always list materials as a separate line item. If CIS applies, this ensures deductions are calculated only on labour. Even for direct customer work, itemising materials builds trust — the customer can see exactly what they're paying for.

Getting Paid Faster

Late payment is endemic in UK trades. These practices help:

Invoice immediately. Send the invoice the day the job is complete, or at the agreed milestone. Every day you delay is a day added to your payment timeline.

State payment terms clearly. "Due within 14 days of invoice date" is unambiguous. "Payment on completion" isn't — completion of what?

Offer multiple payment methods. Bank transfer, card payment, and online payment links all reduce friction. The easier you make it to pay, the faster payment arrives.

Chase promptly. If payment is 3 days overdue, send a polite reminder. If it's 14 days overdue, send a firmer one. Leaving it "because it's awkward" costs you money.

For CIS work: keep payment and deduction statements. Contractors must provide these within 14 days of each tax month end. Chase them if they don't — you need them to reclaim your CIS deductions.

Plumber Invoicing Checklist

1. Invoice sent within 24 hours of job completion
2. Materials and labour itemised separately
3. VAT applied correctly (standard/reduced/zero/reverse charge)
4. CIS deduction line included (if subcontracting)
5. UTR shown on CIS invoices
6. Unique sequential invoice number
7. Payment terms and methods stated
8. Customer details and site address correct

Use the CIS Deduction Calculator to check your net payment before invoicing.

This is general guidance, not tax or legal advice. For VAT registration, CIS, and domestic reverse charge queries specific to your business, consult a qualified accountant.

Sources

• When to register for VAT — GOV.UK
• CIS subcontractor obligations — GOV.UK
• CIS contractor: make deductions and pay subcontractors — GOV.UK