CIS for Plumbers UK: Complete Guide to the Construction Industry Scheme (2026)

What Is CIS and Does It Apply to You?

The Construction Industry Scheme is an HMRC scheme that requires contractors to deduct tax directly from payments made to subcontractors and pass it to HMRC. It applies across the construction industry — which includes plumbing, heating, electrical, roofing, and most other trades that work on building or infrastructure projects.

CIS applies to you as a plumber if you:

• Work as a subcontractor for a main contractor (building companies, developers, main contractors)
• Work on commercial or industrial sites alongside other tradespeople
• Are paid by a company rather than an end customer (homeowner)
• Work on domestic properties but as part of a larger contracted development

CIS does not apply when you work directly for homeowners on their own home — the typical domestic plumbing call-out. But many plumbers do both: domestic work and occasional subcontract work. If you ever do subcontract work, you should be registered.

How to Register as a CIS Subcontractor

Registration is free. You need:

• Your Unique Taxpayer Reference (UTR) — if you don't have one, register for Self Assessment first
• Your National Insurance number
• Your legal name and trading name (if different)
• Your business address

Register online via your Government Gateway account or call the HMRC CIS helpline: 0300 200 3210. Registration typically takes 5–10 working days before contractors can verify your status.

CIS Deduction Rates: 0%, 20%, 30%

The deduction is an advance payment of income tax and National Insurance — not a separate charge. It is offset against your total tax liability when you file your Self Assessment. Most subcontractor plumbers are owed a refund because the flat 20% deduction rate often exceeds their actual effective tax rate once expenses are deducted.

How to Write a CIS Invoice as a Plumber

The single most important rule for CIS invoices: always separate labour and materials as distinct line items. The 20% deduction applies only to the labour element — not materials. If you lump them together, the contractor may deduct 20% from the entire amount, costing you money.

Additional items to include on a CIS invoice:

• Your UTR (Unique Taxpayer Reference)
• A note stating the invoice is subject to CIS deduction
• Your CIS registration status (registered at 20%)
• Labour and materials clearly separated — never combined in one line
• If VAT-registered: your VAT number and VAT calculated on the full amount (VAT applies before CIS deduction)

TraderInvoice lets you create CIS-structured invoices by voice — just mention labour and materials separately when describing your job, and the invoice will itemise them correctly. Read the full guide: How to Invoice as a Self-Employed Plumber in the UK.

Gross Payment Status — What It Is and How to Get It

Gross payment status (GPS) means contractors pay you the full amount of your invoices with no CIS deduction at source. This is the best CIS outcome for cash flow — you receive 100% of your labour income and settle your tax through Self Assessment at the end of the year.

To qualify for GPS as a sole trader plumber, HMRC requires:

• Business turnover in construction of at least £30,000 per year
• All tax returns filed on time for the past 12 months (or 3 years for some checks)
• No outstanding tax debts with HMRC
• The business has been trading for at least 12 months

Apply through your Government Gateway account or by calling the CIS helpline. HMRC reviews your compliance history and typically responds within 28 days. GPS is not permanent — HMRC reviews it annually and can remove it if your compliance record deteriorates.

Monthly CIS Statements from Contractors

Every contractor who makes CIS deductions from your payments must give you a monthly statement showing the deductions made. Keep every CIS statement you receive — they are essential for your Self Assessment tax return and for claiming any refund.

If a contractor fails to provide your monthly statement, you are legally entitled to request it. Report persistent non-compliance to HMRC — contractors who fail to operate CIS correctly face penalties.

How to Reclaim Overpaid CIS Tax

Most subcontractor plumbers receive a CIS refund each year because the flat 20% rate is deducted from gross labour income before expenses — and your actual effective tax rate, after deducting all allowable business expenses, is usually lower than 20%.

The more allowable expenses you claim correctly — see our guide on what a self-employed plumber can claim on tax — the lower your actual tax liability and the larger your CIS refund.

Record Keeping for CIS

For CIS subcontractors, good records are non-negotiable. Keep:

• Copies of all invoices you issue to contractors (numbered, with labour and materials separated)
• Monthly CIS deduction statements from every contractor
• Bank statements showing the net amounts received
• Receipts for all business expenses
• Your UTR and CIS registration confirmation

TraderInvoice stores every invoice as a digital record. For CIS work, create your invoice by voice — the AI separates labour and materials automatically — and your entire invoice history is available to export for your accountant at year end.