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CIS Monthly Return to HMRC

A monthly return submitted to HMRC detailing all payments made to subcontractors and CIS deductions.

Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. Finance Act 2004 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.

Legal basis	Finance Act 2004, Part 3 — Construction Industry Scheme (CIS)
Form	CIS300 — monthly return filed with HMRC by the contractor
Filing deadline	19th of each month following the end of the tax month (tax months run 6th to 5th)
Payment deadline	19th by post / cheque — 22nd if paying electronically
Nil return	Required even when no payments have been made to subcontractors in the tax month
Late filing penalties	£100 (1 day late), £200 (2 months), £300 or 5% of CIS deductions (6 months), £300 or 5% (12 months) — can exceed £3,000

1. The CIS Monthly Return

The CIS monthly return (form CIS300) is the contractor's monthly declaration to HMRC of all payments made to subcontractors under the Construction Industry Scheme. Every contractor registered for CIS must file a return for every tax month, regardless of whether any payments were made to subcontractors during that period. The return reports the gross amounts paid, the CIS deductions made, and identifies each subcontractor by name and Unique Taxpayer Reference.

The filing deadline is the 19th of the month following the end of the tax month. Tax months run from the 6th of one calendar month to the 5th of the next. For example, the return for the tax month 6 March to 5 April must be filed by 19 April. The CIS deductions reported on the return must be paid to HMRC by the 19th of the same month (or the 22nd if paying electronically). Late filing attracts automatic penalties: £100 for one day late, £200 at two months, and £300 or 5% of the CIS deductions due (whichever is higher) at six and twelve months. For a contractor with significant subcontractor payments, penalties can quickly exceed £3,000.

A nil return must be filed even when no payments to subcontractors were made during the tax month. Many contractors assume that if they have not made any payments, they do not need to file — this is incorrect. HMRC expects a return every month and will impose late filing penalties if a return is not received, regardless of whether any deductions were due. The only way to stop the requirement to file monthly returns is to formally notify HMRC that you are no longer operating as a CIS contractor.

Set a calendar reminder on the 15th of every month

The CIS monthly return is due by the 19th. Setting a recurring reminder on the 15th gives you four working days to compile the return, check the figures, and file before the deadline. This is particularly important during busy periods when administrative tasks can be deprioritised. A single missed deadline triggers an automatic £100 penalty — and once the pattern starts, the penalties escalate rapidly.

2. CIS Monthly Return Content

The CIS300 return must include the following information. The return covers all payments made to subcontractors during the tax month and must be accurate and complete before filing.

Field	Detail
Contractor details	Contractor's legal name, employer's PAYE reference, and accounts office reference
Tax month	The tax month the return covers (e.g. 6 March to 5 April) and the tax year
For each subcontractor — name	Full legal name of the subcontractor (individual name for sole traders, company name for limited companies)
For each subcontractor — UTR	The subcontractor's Unique Taxpayer Reference as confirmed during HMRC verification
For each subcontractor — verification number	The verification reference number issued by HMRC when the subcontractor was verified
For each subcontractor — gross amount	Total gross payment made to the subcontractor in the tax month (before deduction)
For each subcontractor — materials	Cost of materials included in the payment (not subject to CIS deduction)
For each subcontractor — CIS deduction	Tax deducted at the applicable rate (20%, 30%, or 0%) from the labour element of the payment
Totals	Total gross payments, total materials, total CIS deductions, and total net payments across all subcontractors for the tax month
Nil return declaration	If no payments were made to subcontractors in the tax month, the return must include a nil return declaration — this is still mandatory
Declaration	A declaration that the information provided is correct and complete, signed by the contractor or an authorised representative
Filing method	Filed online via HMRC's CIS online service, commercial software, or (in limited circumstances) on paper

3. Common Mistakes

Not filing a nil return

If no payments were made to subcontractors during a tax month, the contractor must still file a nil return by the 19th. HMRC does not know whether you made payments or not — it simply expects a return every month. A missing return is treated as a late return and attracts the same automatic penalties as a late return with deductions. Many contractors have accumulated thousands of pounds in penalties because they did not realise that nil returns were required. The only way to stop the filing obligation is to formally deregister as a CIS contractor with HMRC.

Missing subcontractors from the return

Every subcontractor who was paid during the tax month must be included on the return. Omitting a subcontractor — whether by accident or because the payment was small — creates a discrepancy between the return and the actual payments made. HMRC cross-references CIS returns with subcontractors' tax returns. If a subcontractor claims a CIS deduction that does not appear on the contractor's return, HMRC will investigate. This can trigger an enquiry into all of the contractor's CIS records and may result in penalties for incorrect returns.

Incorrect UTRs

The Unique Taxpayer Reference for each subcontractor must exactly match the UTR confirmed during HMRC verification. Transposing digits, using an old UTR, or using a personal UTR instead of a company UTR are common errors. An incorrect UTR on the return means that HMRC cannot match the deduction to the subcontractor's tax record, which causes problems for the subcontractor when they try to reclaim their deductions. It can also trigger queries from HMRC to the contractor. Always copy the UTR directly from the verification confirmation.

4. Frequently Asked Questions

How does a subcontractor claim back CIS deductions?▾

A sole trader or partnership subcontractor claims back CIS deductions through their annual Self Assessment tax return. The deductions are treated as advance payments of Income Tax and National Insurance. If the total CIS deductions exceed the tax due, the subcontractor receives a refund from HMRC. A limited company subcontractor offsets CIS deductions against its monthly PAYE and National Insurance liabilities (reported through RTI), or against its Corporation Tax liability. If the deductions exceed these liabilities, the company can claim a refund. In both cases, the subcontractor needs the payment and deduction statements (PDS) issued by the contractor as evidence of the deductions made. This is why it is critical that contractors issue accurate PDS documents within the 14-day deadline.

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