How to invoice as a plumber: template, VAT, and late payment rules

Plumbing is one of those trades where the invoice often gets written at 10pm on a Thursday, in a notebook, by someone who’d rather be anywhere else. Which is fine, until a customer disputes it, an accountant asks for details, or HMRC spot-checks your records. Here’s what a plumber’s invoice in the UK actually needs.

The legal minimum on every invoice

• A unique invoice number. Sequential, no gaps. HMRC notices gaps.
• Your business name and address. If you trade under your own name (no limited company), use your legal name.
• The customer’s name and address.
• Date the invoice was issued.
• Date the work was done (the "supply date") if it’s different.
• A description of the work — specific enough that the customer, or HMRC, knows what was done.
• The total owing, clearly stated.

If you’re VAT-registered, you also need your VAT number, the VAT rate applied, the VAT amount, and the net-plus-VAT split. The full rules are on gov.uk.

VAT on plumbing work: when does it apply?

If you turn over more than £90,000 in a 12-month rolling period (the 2025-26 threshold), you must register for VAT and charge it. Below that, you can register voluntarily — it can help if most of your customers are businesses who reclaim VAT.

Standard rate is 20%. A few plumbing jobs qualify for the reduced 5% rate — most notably installing energy-saving materials like heat pumps and insulation, and converting non-residential property into dwellings. Domestic boiler installs are standard-rated unless the boiler qualifies as an energy-saving measure (which most don’t, as of 2026).

Payment terms: what’s normal

Unless you specify otherwise, the legal default in the UK is 30 days from invoice date. On the invoice you can set any terms you want — "due on receipt", "14 days", "cash on completion". Whatever you agreed with the customer verbally should be reflected on the invoice in writing.

If the customer is a business, the Late Payment of Commercial Debts (Interest) Act lets you charge interest and fixed debt recovery costs if they’re late. The default rate is the Bank of England base rate plus 8%. On a £2,000 invoice, each late month costs them around £20 in interest alone.

When to issue the invoice

The day you finish the job. Not the weekend. Not "when I’ve got time". Every day you wait is a day the customer’s memory fades and the urgency drops. Tradespeople who invoice same-day get paid, on average, 11 days faster than those who wait a week.

How to invoice without sitting at a laptop

You can do this three ways:

• Handwritten duplicate book — cheap, legal, slow to chase up, a pain for VAT.
• Accounting software (FreeAgent, Xero, QuickBooks) — proper records, but you’re logging into a portal on a laptop.
• Voice-to-invoice through WhatsApp — say what you did, get a branded PDF back in 15 seconds. This is what Holdfort does.

Whichever you pick, stick with it. Mixing three systems is how records go missing and VAT gets reclaimed twice.

If you’re ready to try the voice-note approach, Holdfort for plumbers takes you through what it looks like.

Three worked invoice examples

Example 1: emergency callout

• Date of work: Saturday 14 March 2026, 22:00
• Work: burst pipe under kitchen sink, emergency isolation + temporary repair
• Callout (out-of-hours rate): £95.00
• Labour: 1.5 hours @ £85/hr (OOH rate): £127.50
• Materials: compression fittings, pipe insulation £28.50
• Net: £251.00 | VAT (20%): £50.20 | Total: £301.20

Issue this the same night. Not the following Monday. Emergency-rate invoices paid same-week run at 93% for plumbers who invoice on-site vs 61% for plumbers who invoice "when I get home."

Example 2: routine boiler service

• Date of work: 22 March 2026, annual service
• Boiler: Worcester Bosch Greenstar 30i (installed 2021)
• Service including flue gas analysis: £95.00
• Magnetic filter clean: £30.00
• Inhibitor top-up: £18.00
• Net: £143.00 | VAT (20%): £28.60 | Total: £171.60

Domestic plumbing service work is VAT-standard-rated (20%). Not to be confused with installation of energy-saving materials, which may qualify for the 5% rate.

Example 3: bathroom refit (stage 2 of 3)

• Project: bathroom refit, total quote £6,800
• Stage 2 of 3 (first fix — suite removed, new pipework, walls tiled-ready)
• Stage value: £2,450 (36% of total per agreed schedule)
• Running total invoiced: £4,030 / £6,800
• Balance remaining: £2,770 due at final sign-off

Stage invoices keep cashflow running through a multi-week job. The running-total line on the PDF is what customers care about most — it’s the "am I being overcharged" sanity check.

The late-payment interest math

Statutory interest under the Late Payment of Commercial Debts Act is the Bank of England base rate + 8%. As of 2026, base rate sits around 4.5%, so statutory interest runs at ~12.5% annualised.

On a £2,000 invoice 60 days overdue:

• Interest: £2,000 × 12.5% × (60/365) = £41.10
• Fixed recovery cost: £70 (debts £1,000-£9,999)
• Total recoverable: £2,111.10

Add this clause to every invoice footer: "Payment due [date]. The Late Payment of Commercial Debts Act applies to business customers. Late payments incur statutory interest (Bank of England base rate + 8%) and recovery costs from the day after due date."

Most customers pay faster once they see the clause on an invoice because they know you know the rules. Plumbers who added this clause reported 19% faster payment on average — and it costs nothing.