How do I claim a CIS refund as a plumber?

On your tax return, once the tax year ends on 5 April. For 2026-27 a sole trader plumber can file from 6 April 2027. Once you are in Making Tax Digital, the refund is requested separately through HMRC online services.

Under the Construction Industry Scheme (CIS), a contractor takes 20% from the labour part of what it pays you if you are registered, or 30% if it cannot verify you. That is an advance payment towards your Income Tax and National Insurance. Plumbers often supply the boiler, cylinder or bathroom suite, and much of their work is for homeowners, so the materials and the domestic work both shape the refund. Over-deducted CIS is claimed back through your tax return. The sooner after 5 April you file, the sooner HMRC can repay you. This page is for sole traders and follows GOV.UK as checked on 18 October 2026. A limited company uses its deductions through its payroll instead, as our guide on whether a limited company can claim back CIS deductions explains.

How the claim works

Making Tax Digital for Income Tax (MTD) started on 6 April 2026 for sole traders whose 2024-25 return showed over £50,000 of self-employed and rental income before costs. It starts on 6 April 2027 for those over £30,000 on the 2025-26 return.

A worked example for a plumber

Sam is a self-employed plumber outside Scotland with no other income. In 2026-27 a contractor pays him £28,000 before deductions for installing heating and bathrooms in new flats: £20,000 labour and £8,000 for materials he bought. The contractor takes 20% of the labour only, which is £4,000. Sam also earns £6,000 from repairs and boiler swaps for homeowners. Apart from the materials, his van, tools, insurance and phone cost £5,000.

If the contractor had taken 20% off the whole £28,000, it would have deducted £5,600. The extra £1,600 would come back too, but only after the year ends. These are 2026-27 rates. Class 2 National Insurance is treated as paid because his profit is above £7,105. This is an example only.

Steps to claim your CIS refund

1. Collect every payment and deduction statement for the tax year, 6 April to 5 April. A contractor who takes a deduction must give you one within 14 days of the end of that tax month, showing the gross amount, materials and deduction.
2. Ask for copies of any missing statements. If a contractor has closed, write to HMRC with your details, the contractor's details, the dates you were paid and why you have no statements.
3. Check each statement against your bank account and against the materials on your invoice.
4. Total your homeowner income, including cash jobs, and keep your merchant receipts for every material you bought.
5. If you are not in MTD for the year, put your total turnover and your CIS deductions on your Self Assessment return, give your bank details and file online.
6. If you are in MTD, check the CIS deductions HMRC has added to your MTD tax return, correct them in your software if needed, submit, then request the refund through your HMRC online services account.

What this means for you

Sam's £34,000 of turnover is over £30,000, so if his 2025-26 return was similar he joins MTD on 6 April 2027. His 2026-27 return is still an ordinary Self Assessment return, so he claims this refund in it. From 2027-28 he requests any refund through his HMRC online services account after submitting.

Your deductions sit with HMRC until your return is in. The deadline for a 2026-27 return is 31 January 2028, so filing in April puts your claim in up to ten months sooner. Showing materials separately on every invoice keeps the deduction to the labour, so less of your money waits with HMRC in the first place.

If something looks wrong

• A contractor took 30%. GOV.UK says your details must match your registration exactly. Speak to the contractor; the extra still counts on your return.
• HMRC's figures differ from your statements. Our guide on checking your CIS deductions with HMRC sets out each route.

Use the free MTD check to see when MTD starts for you, and the trades section for more guides for plumbers.