How to Invoice as a Self-Employed Plumber in the UK (2026 Guide)

1. What must a plumber's invoice include by law?

HMRC doesn't have a single specific law that dictates invoice format for sole traders, but there are clear requirements set out across the Companies Act, VAT regulations, and HMRC guidance that you must follow. A compliant plumber's invoice must include:

• ·Your full name (or business name) and address
• ·Your customer's name and address
• ·A unique, sequential invoice number
• ·The invoice date
• ·The supply date (if different from the invoice date)
• ·A clear description of the work carried out (e.g. 'Supply and fit 22mm isolation valve, kitchen sink, 14 March 2026')
• ·The amount charged — labour and parts broken out separately is best practice
• ·Your payment terms and due date
• ·If VAT registered: your VAT registration number, the VAT rate applied, and the VAT amount

If you trade under a business name (e.g. "Dave's Plumbing Services") but operate as a sole trader, you must also include your personal name on the invoice. For example: Dave Smith trading as Dave's Plumbing Services.

It's also good practice — though not legally required for non-VAT-registered sole traders — to include your contact number and email address. It makes chasing payment easier and looks more professional.

2. How to number your invoices

Invoice numbers must be unique and sequential — HMRC expects a clear, unbroken audit trail. You cannot reuse a number or delete invoices to "fix" your records. If you make an error, issue a credit note instead.

Common formats that work well for plumbers:

• ·INV-0001, INV-0002, INV-0003 — simple, clean, widely understood
• ·2026-001, 2026-002 — year-prefixed, resets each tax year
• ·PLB-2026-001 — trade-prefixed if you manage multiple businesses

The most important rule: never have gaps. If an inspector sees INV-0001, INV-0002, INV-0004 with no INV-0003, they will ask questions. If you use invoicing software like TraderInvoice, numbering is handled automatically so you never need to think about it.

3. VAT rules for self-employed plumbers

VAT registration is mandatory once your taxable turnover exceeds £90,000in any rolling 12-month period (the 2026 threshold). Below that, it's optional — but there are reasons you might choose to register voluntarily, such as reclaiming VAT on tools, vans, and materials.

VAT rates for plumbing work

Most standard plumbing jobs (repairs, maintenance, fitting bathrooms) are charged at the standard rate of 20%. However, there are important reduced-rate and zero-rate exceptions:

• ·New residential builds — zero-rated (0%) on labour and some materials
• ·Certain energy-saving materials (heat pumps, solar thermal) — 0% since April 2022
• ·Work for disabled people (e.g. wet room adaptations, stair lifts) — reduced rate or zero-rated in some cases
• ·Converting a non-residential building into dwellings — 5%

If you are VAT registered, your invoice must show your VAT registration number, clearly state the VAT rate applied to each line, and show the VAT amount and the total including VAT. HMRC refer to this as a "VAT invoice."

4. CIS — Construction Industry Scheme

If you work as a subcontractor for a main contractor (rather than directly for homeowners), you almost certainly need to be aware of the Construction Industry Scheme (CIS).

Under CIS, the contractor is required to deduct tax from your payments and send it directly to HMRC:

• ·20% deduction — if you are registered with HMRC under CIS
• ·30% deduction — if you are not registered (a strong reason to register)
• ·0% deduction — if you have 'gross payment status' (requires a clean tax record and minimum turnover)

How CIS affects your invoices

CIS deductions apply only to the labour element of your invoice — not to the cost of materials. This means you must clearly separate labour and materials on every invoice you send to a contractor. For example:

The contractor will give you a monthly CIS statement showing deductions made. You use these figures when completing your Self Assessment tax return to reclaim or offset the tax already paid.

Registering for CIS is free and takes minutes on the HMRC website. If you are doing any subcontract work and you have not registered, do it now — you are losing 10% of your labour income unnecessarily.

5. Setting payment terms

Payment terms tell your customer when you expect to be paid. Being explicit about this on every invoice — and agreeing terms before starting work — dramatically reduces disputes and late payment.

Common payment terms for plumbers

• ·Domestic customers: payment on completion, or a 25-50% deposit upfront with balance on completion
• ·Commercial clients: 14 days net or 30 days net from invoice date
• ·Emergency call-outs: payment on the day (card machine or bank transfer)
• ·Larger projects: stage payments tied to milestones (first fix, second fix, commissioning)

Always state your payment terms in writing — ideally in a short quote or job confirmation email before work starts, and then again on the invoice itself. A line such as "Payment due within 14 days. Bank transfer preferred. Account details below." is sufficient.

Include your bank details on every invoice: account name, sort code, and account number. The easier you make it to pay, the faster you get paid.

6. What to do when customers don't pay

Late payment is the most common financial problem for self-employed plumbers. Here's a step-by-step approach:

7. Record keeping for tax

As a self-employed plumber, you must keep records of all invoices issued and all business expenses for at least 5 years after the 31 January Self Assessment deadline for that tax year (so effectively 6 years from the end of the tax year). HMRC can investigate going back this far.

What to keep:

• ·Copies of all invoices you issue (numbered, with dates)
• ·Receipts and invoices for all business expenses (tools, materials, van, fuel, PPE, insurance, phone)
• ·Bank statements
• ·CIS deduction statements from contractors (if applicable)
• ·VAT records if you're VAT registered

Digital records are perfectly acceptable — and preferred, as they're harder to lose than paper. Using invoicing software built for tradespeople means your invoice history is always organised, searchable, and ready for your accountant at year end.

8. Frequently Asked Questions