How to Verify Subcontractors and File Monthly CIS Returns
This guide outlines the critical steps for UK contractors to verify subcontractors and file Construction Industry Scheme returns during the 2026/27 tax year, covering important changes implemented from April 2026.
To verify a subcontractor and file your monthly Construction Industry Scheme (CIS) return, you must login to the HMRC CIS online service or use compatible filing software. You submit the subcontractor's details to verify their tax deduction rate before making any construction payments. Under Schedule 11 of the Finance Act 2004, you then withhold the appropriate tax amount from their invoice and submit the monthly CIS300 return to HMRC by the 19th of each calendar month.
Key Takeaways for UK Contractors in 2026/27
Navigating your obligations in the 2026/27 tax year requires strict adherence to updated compliance guidelines from His Majesty's Revenue and Customs (HMRC). Essential details and administration updates include:
- Filing updates: From 6 April 2026, failing to file a return during inactive months triggers automated penalties, making nil returns or inactivity requests strictly mandatory.
- Local authority exemption: Under the 2026 CIS simplification measures, payments to local authorities and specific public bodies are completely outside the scope of the scheme.
- Verification rates: Tax deductions remain structured at 0% for gross payment status, 20% for registered subcontractors, and 30% for unregistered partners.
- Strict deadlines: All monthly returns must reach HMRC by the 19th of the following month, with late electronic payments penalised after the 22nd.
How do I verify a subcontractor and file my monthly CIS return?
Verify subcontractors via HMRC online using their Unique Taxpayer Reference, and file your monthly return by the 19th.
First, retrieve the subcontractor's name, National Insurance number, and registration details, then input them into the HMRC CIS online portal. The system will calculate whether to deduct tax at 0%, 20%, or 30%. Finally, declare these payments on the official CIS300 return by the 19th of each month, paying over any withheld tax electronically by the 22nd.
What is the Construction Industry Scheme (CIS)?
The Construction Industry Scheme (CIS) is a UK tax framework requiring contractors to deduct money from subcontractor invoices to pay directly to HMRC.
This scheme, established under the Income Tax (Construction Industry Scheme) Regulations 2005, serves as an advance tax contribution system. It covers most construction work on permanent or temporary buildings within the UK, extending to civil engineering and installation activities. Any business paying others for construction jobs must register as a contractor and calculate statutory withholdings.
When do you need to verify a subcontractor under CIS?
You must verify a subcontractor before making your very first payment to them for construction services.
According to the HMRC internal manual CISR51010, you must run a check before issuing any compensation under the agreement. You only need to re-verify a subcontractor if you have not made any payments to them during the current or previous two tax years. Allowing this period to expire without a transaction makes them inactive, requiring fresh validation.
What information do you need from the subcontractor?
Contractors need precise tax and corporate identifying data from each entity to verify them accurately.
- The subcontractor's Unique Taxpayer Reference (UTR), which is always required and contains 10 digits.
- Their National Insurance number (NINO), which is required if they operate as a sole trader or individual.
- The Company Registration Number (CRN), which is essential if the subcontractor operates as a limited company.
- The exact legal name or trading name used for tax registration, plus individual partner UTRs if the subcontractor is registered as a business partnership.
How to verify a subcontractor online with HMRC
Log in to the HMRC CIS online service using your Government Gateway credentials to submit the subcontractor's data.
This system immediately cross-references details with official tax records to dictate your deduction requirements. You may also handle verification using compatible third-party CIS commercial software that links directly to HMRC's Gateway. The service generated will return a specific verification reference number for your internal records.
What are the subcontractor verification deduction rates?
The legal deduction rates depend entirely on the subcontractor's registration status under official HMRC guidelines:
| Verification Status | Deduction Rate | Contractor Action |
|---|---|---|
| Gross Payment Status | 0% | Pay the full invoiced amount without deduction. |
| Registered (net) | 20% | Deduct tax on the labour portion of the invoice only. |
| Not registered / unmatched | 30% | Deduct the higher rate tax on all non-material costs. |
What are the rules for deducting CIS on invoices?
Deductions under the CIS scheme apply strictly to the labour portion of the invoice, excluding raw material costs.
When processing invoices, you must separate materials, plant hire, fuel, and Value Added Tax (VAT) from the base labour cost. Only the remaining labour portion is subjected to the 20% or 30% tax deduction. After processing, contractors must provide the subcontractor with a Payment and Deduction Statement within 14 days of the end of the tax month.
How do you file your monthly CIS return (CIS300)?
File your return online via the HMRC portal by the 19th of the calendar month following the tax month.
The monthly period runs from the 6th of one month to the 5th of the following month. For example, payments made between 6 May and 5 June require a filed return by 19 June. For each subcontractor, you must report the gross value, net amounts, and verification reference. You must also include a formal declaration confirming that the employment status of each individual has been correctly assessed.
What are the new CIS rules for 2026/27?
Major administrative simplifications and standardisations took effect starting from the 6 April 2026 tax year.
Under the new CIS Simplification policies, local authorities and certain designated public bodies are removed from the scope of CIS. Furthermore, the mandatory nil return and formal inactivity request framework is fully reinstated. Unreported quiet periods will no longer be ignored, and failure to notify HMRC of zero activity will result in penalties.
What are the penalties for late CIS returns?
Missing the 19th filing deadline triggers automated, escalating late filing penalties from HMRC.
| Duration of Delay | Penalty Amount |
|---|---|
| 1 day late | £100 initial automatic fine |
| 2 months late | £200 additional fine |
| 6 months late | £300 or 5% of CIS deductions (whichever is higher) |
| 12 months late | £300 or 5% of deductions (often rising to £3,000+ for persistent failure) |
| Incorrect employment status declaration | Up to £3,000 |
A practical compliance checklist for contractors
Maintaining a rigorous compliance timeline protects construction firms from costly disruptions and regulatory fines.
- Set a permanent calendar reminder for the 19th of every month.
- Verify all newly contracted subcontractors before processing any first-time receipts.
- Keep verification records and reference numbers for at least 3 years to satisfy compliance guidelines.
- Isolate labour costs from equipment and materials on all subcontractor worksheets.
- Distribute the formal Payment and Deduction Statement within 14 days of the tax month end.
- Submit a nil return if no payments are distributed within a given tax month.
What happens if I cannot match a subcontractor's details on HMRC?
If HMRC's database cannot match the details, the subcontractor is verified as unmatched. You must apply the higher 30% deduction rate on their labour invoices and record the unique unmatched verification reference number issued by HMRC.
Do I have to file a CIS return if I did not make any payments to subcontractors?
Yes, starting from 6 April 2026, nil returns are mandatory. If you have not paid any subcontractors, you must submit a nil return by the 19th or file an inactivity request in advance which covers up to six months.
Are local authorities subject to CIS verification in 2026/27?
No. Under the CIS simplification rules introduced for the 2026/27 tax year, local authorities and public bodies are excluded from the scope of CIS, meaning verification is not required.
Can I appeal a late filing penalty from HMRC and what is the deadline?
Yes, you can appeal a penalty online or in writing, but not by phone. The strict legal deadline to submit your appeal is 30 days from the date of the penalty notice.
How long do I need to keep CIS verification reference numbers on file?
You are required to keep all CIS Records, including verification references and payment vouchers, for at least 3 years after the end of the tax year they relate to.