CIS (Construction Industry Scheme) in the UK: A Complete Guide for Contractors and Subcontractors
The Construction Industry Scheme (CIS) is a UK HMRC tax system that requires contractors to deduct money from payments to subcontractors before paying them. These deductions count as advance payments towards the subcontractor’s income tax and National Insurance contributions. It applies to most construction work carried out in the UK — including building, demolition, refurbishment, and site preparation — and affects both sole traders and limited companies operating in the sector.
How CIS Works: Core Obligations for Contractors
Contractors in the UK construction industry must register with HMRC for CIS before hiring any subcontractor. Once registered, they must verify each subcontractor’s CIS status via HMRC’s online service or telephone before making the first payment. This verification returns one of three outcomes: 20% deduction (subcontractor is registered), 30% deduction (unregistered), or 0% (gross payment status granted by HMRC). Contractors must deduct the correct rate from the labour portion of each payment — not materials — and pay those deductions to HMRC monthly. They must also file a CIS300 monthly return by the 19th of the following month, reporting all payments made, deductions taken, and subcontractor details. Failure to verify or file on time can trigger penalties, interest, and loss of gross status eligibility. Contractors must keep full records for at least three years, including verification confirmations, invoices, and proof of deductions paid. Importantly, CIS does not replace PAYE obligations — if a worker is an employee, standard PAYE applies instead of CIS.
Subcontractor Responsibilities and Gross Status
Subcontractors must register for CIS with HMRC before starting construction work — registration is mandatory unless exempt (e.g., certain small businesses meeting strict criteria). Upon registration, HMRC assigns a unique CIS reference number and assesses eligibility for gross payment status, which allows receiving payments without deductions. To qualify, subcontractors must pass three tests: the business test (operating commercially with own equipment), the turnover test (minimum £30,000 annual turnover excluding VAT), and the compliance test (good record on tax returns and payments). Gross status is not automatic and must be applied for separately; it can be revoked if compliance lapses. Subcontractors receive a CIS statement (form CIS304) from each contractor quarterly, summarising deductions made. These statements are essential for completing Self Assessment tax returns — the deducted amounts are credited against final tax liability. Subcontractors must also report all CIS income and expenses accurately and retain invoices, bank statements, and CIS statements for at least five years for HMRC audit purposes.
CIS Deduction Rates and Calculation Rules
CIS deduction rates are strictly defined by HMRC and depend solely on the subcontractor’s verified status: 20% for registered subcontractors, 30% for unregistered ones, and 0% for those holding valid gross payment status. Crucially, deductions apply only to the labour element of a payment — not to materials, plant hire, or VAT. For example, on a £5,000 invoice comprising £3,500 labour and £1,500 materials, only £3,500 is subject to deduction. Contractors must calculate deductions before VAT is added. If a subcontractor is VAT-registered, the labour amount should be stated net of VAT. HMRC provides detailed guidance on apportioning mixed supplies, and misclassifying materials as labour may lead to under-deduction penalties. Contractors must also account for ‘labour-only’ vs. ‘mixed’ contracts correctly — subcontractors supplying only labour fall squarely under CIS, while those acting as principal contractors on subcontracts may have additional responsibilities. Accurate record-keeping of breakdowns is essential, as HMRC may request evidence during compliance checks. Using accounting software with CIS functionality helps ensure consistent application of rates and proper segregation of labour and materials.
Monthly CIS Returns, Reporting Deadlines, and Tax Offsets
Contractors must submit a CIS300 monthly return to HMRC by the 19th of the month following the reporting period — e.g., payments made in May must be reported by 19 June. The return includes total payments made, total deductions taken, and individual subcontractor details (name, UTR, verification status, and amounts). Late filing incurs automatic penalties: £100 for up to 2 months late, rising to £200 beyond that, plus potential daily penalties for persistent failure. Payments of deducted tax must also reach HMRC by the same 19th deadline — typically via BACS or CHAPS. These CIS deductions are treated as advance payments toward the subcontractor’s income tax and Class 4 NIC liabilities, and they appear on the subcontractor’s SA302 tax calculation. Contractors can offset their own CIS deductions against their PAYE and NIC liabilities when filing their Full Payment Submission (FPS) — but only if they’re also employers and use HMRC’s Basic PAYE Tools or compatible payroll software. Subcontractors claim credit for CIS deductions on their Self Assessment return (SA100), reducing their final tax bill. Any overpayment is refunded automatically after submission and processing — no separate claim is needed.
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Can a subcontractor switch from 20% to gross payment status mid-year?
Yes — subcontractors can apply for gross payment status at any time via HMRC’s online service or form CIS42. Approval depends on passing all three tests (business, turnover, compliance) at the time of application. If approved, the 0% rate applies to all future payments from verified contractors, but past deductions remain unchanged and are still claimable on the next Self Assessment return.
What happens if a contractor pays a subcontractor before verifying their CIS status?
If verification isn’t completed before the first payment, HMRC mandates a 30% deduction regardless of the subcontractor’s actual registration status. The contractor remains liable for this higher deduction and cannot reclaim the excess later. Verification must occur before payment — retroactive verification does not reduce the required deduction for that initial payment.
Do CIS deductions count toward a subcontractor’s state pension entitlement?
No — CIS deductions are income tax and Class 4 NIC prepayments only. They do not count as Class 2 or Class 3 NIC contributions, which are required for state pension credits. Subcontractors must pay Class 2 NIC separately (if self-employed and earning over £6,725/year) or make voluntary Class 3 contributions to protect pension entitlement.
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