Self-employed plumbers are among the most consistently overpaid workers in CIS. The 20% deduction on labour income adds up fast across a full year of jobs, and materials costs (pipework, fittings, boiler parts) are excluded from the deduction base entirely. The result: most plumbing subcontractors have a significant CIS refund sitting unclaimed at HMRC.
CIS deductions apply only to the labour element of an invoice. The cost of materials you supply for a job is excluded from the deduction base. Many main contractors apply the 20% rate to the full invoice value rather than splitting out materials. If yours do, you are overpaying on every job. We review your deduction slips and identify overpayment.
Self-employed plumbers drive significant mileage between jobs. From 6 April 2026, the AMAP rate for cars and vans is 55p per mile for the first 10,000 miles. Tools, PPE, trade subscriptions and your phone bill are also allowable. Many plumbers claim only a fraction of what they are entitled to, leaving real money on the table.
At higher income levels, operating through a CIS-registered limited company can be significantly more tax-efficient than sole trader. The company reclaims CIS deductions in real time via EPS rather than waiting for the annual Self Assessment return. We model both structures for your income level and show you the numbers.
Unregistered subcontractors suffer 30% deductions instead of 20%. If you registered for CIS but your contractor cannot verify you, you may be on the higher rate unnecessarily. We check your registration status and fix any verification issues with HMRC.
We calculate the full CIS refund you are owed, account for allowable expenses (mileage at 55p, tools, materials, van costs, PPE), and submit your Self Assessment return to claim it back. Most plumbers receive their refund within 8 to 12 weeks of submission.
Annual Self Assessment, CIS records management, quarterly updates if you are in scope for Making Tax Digital from April 2026. We handle it so you do not have to.
If you earn over £30,000 net of materials per year, you may qualify for gross payment status, meaning no deductions at all. We handle the application and the ongoing compliance that keeps it in place. See our GPS service for full details.
“I had no idea my contractor was taking the 20% off the full invoice. Once we split out the materials properly and claimed the mileage, the refund was considerably larger than expected.”
Composite snapshot based on client patterns. Name and figures anonymised. The tax mechanics are real.
Book a free call. We will talk through your CIS position, your deduction history and whether there is anything worth changing. No hard sell, no obligation.
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