What are CIS Returns? A Complete Guide for UK Contractors
If you work in the UK construction industry, chances are you’ve dealt with the Construction Industry Scheme (CIS) at some point. The scheme was introduced by HMRC to help prevent tax evasion and ensure that tax is deducted correctly at source from subcontractor payments. In other words: it keeps the sector compliant, structured, and accountable.
Where many businesses start to feel less confident is with the monthly CIS Return. Contractors often aren’t sure what needs to be reported, who must submit the return, which deadlines apply, or what happens if something goes wrong.
A CIS Return is HMRC’s monthly check-in to confirm you’ve accurately recorded all subcontractor payments and applied the correct rate of CIS tax (20%, 30%, or 0% for gross status). Miss a deadline, submit incorrect figures, or overlook a subcontractor verification, and HMRC can issue late filing penalties, interest charges, or open a compliance review. These can add up quickly if not managed carefully.
This post looks at what you need to know about CIS Returns in a practical, contractor-friendly way, including:
- What a CIS Return actually is and how it works in day-to-day construction accounting
- Who must file a CIS Return each month (and the situations where you don’t need to)
- Key deadlines every UK contractor should have in their calendar
- Common CIS mistakes that trigger penalties and how to avoid them with simple checks
- Time-saving tools and accounting software that streamline CIS and cut admin time each month
Tip: Keep HMRC’s official CIS guidance to hand for quick reference – it’s updated regularly with rule changes and filing requirements. You can find it here: HMRC – What Contractors Must Do Under CIS.
By the end of this post, you will hopefully have a clear understanding of how CIS Returns work, how they affect your tax position, and how to stay fully compliant without unnecessary stress. And if you’d prefer an expert to take it off your plate entirely, the team at Accounting Wise can handle your CIS Returns, verify subcontractors, and keep your records audit-ready – so you can stay focused on running your business.
What are CIS Returns?
CIS Returns are monthly statutory reports that contractors must submit to HMRC under the Construction Industry Scheme (CIS). These reports give HMRC a clear, verifiable record of your subcontractor activity for the month. In practice, that means telling HMRC exactly:
- Which subcontractors you paid
- How much you paid each subcontractor
- How much CIS tax you deducted at 20% or 30%
- Which subcontractors you verified with HMRC before paying them
The core purpose behind CIS Returns is transparency. Construction is a high-risk sector for undeclared income, so HMRC uses these monthly submissions to confirm that contractors are making the correct tax deductions and that subcontractors are being taxed accurately and fairly.
If you’re a contractor (including deemed contractors such as large property businesses or organisations that spend above the CIS threshold), filing monthly CIS Returns is a legal obligation. Even if you made no subcontractor payments in a given month, you must still submit a “nil return” – failing to do so can trigger late filing penalties.
If you’re a subcontractor, you normally won’t file CIS Returns yourself. However, the information contractors report each month directly impacts your own tax position. CIS deductions recorded on these returns count as tax you’ve already paid, which means:
- You may be owed a refund if too much tax has been deducted during the year
- Your total tax bill will be reduced when you complete your Self Assessment or company tax return
For example, if you receive a £2,000 payment from a contractor and £400 (20%) is deducted under CIS, the contractor will include that £400 on their CIS Return. HMRC will then treat this as £400 of tax you’ve already paid, reducing your final tax bill or boosting your refund when you file your own return.
Because these figures flow directly into HMRC’s systems, incorrect or late CIS Returns can easily lead to repayment delays, penalties, compliance checks, or disputes over tax already paid. Getting them right isn’t just an admin task – it protects both you and your subcontractors from unnecessary complications.
For official HMRC guidance, you can read: HMRC – File Your CIS Return.
Who Needs to File CIS Returns?
You must file CIS Returns if HMRC classifies you as a contractor under the Construction Industry Scheme. This applies not only to traditional construction businesses, but to any organisation that pays subcontractors for construction-related work. You are treated as a contractor if you:
- Pay subcontractors to carry out construction work as part of your business operations
- Spend more than £3 million on construction projects within any rolling 12-month period – even if construction is not your main trade (for example: property developers, large retailers, charities, housing associations, or public bodies commissioning major building work)
If you fall into either category, filing a monthly CIS Return is a legal requirement. This applies even if you made no subcontractor payments during the period. In that case, you must still submit what HMRC calls a nil return. Missing a nil return is treated the same as missing a standard submission and can trigger automatic penalties.
Subcontractors do not file CIS Returns themselves, but they are still heavily impacted by what the contractor reports. Every deduction recorded on a contractor’s CIS Return is treated as tax the subcontractor has already paid. This means:
- Sole traders claim CIS deductions back through their Self Assessment return
- Limited companies claim CIS deductions as a credit against their Corporation Tax bill
This makes accurate reporting essential, as incorrect figures can delay repayments or cause tax mismatches within HMRC’s systems.
To summarise clearly:
- Contractors must register for CIS and file a monthly CIS Return with HMRC.
- Subcontractors keep records of deductions and reclaim them via their annual tax returns.
If you’re unsure whether your business qualifies as a contractor , particularly if you only hire subcontractors occasionally, HMRC’s rules are stricter than most people expect. Oversights can lead to higher 30% deduction rates for subcontractors, compliance checks, and avoidable penalties.
Tip: As soon as you decide to bring in subcontractors, register as a contractor with HMRC before making any payments. It’s quick to do and prevents costly issues later.
Official guidance is available here: HMRC – Contractors and Subcontractors under CIS.
How Do CIS Returns Work?
The Construction Industry Scheme is designed to make sure tax is correctly deducted and reported at every stage of the contractor–subcontractor relationship. In practice, CIS Returns follow a clear monthly workflow. Here’s how the process works step by step:
Verify each subcontractor with HMRC
Before you pay a subcontractor for the first time (or if their details change), you must verify them with HMRC. This tells you which deduction rate to apply:
- 20% – for most registered subcontractors
- 30% – for subcontractors who are not registered under CIS or where HMRC cannot match their details
- 0% – for subcontractors with Gross Payment Status, who are paid in full and then account for tax through Self Assessment or Corporation Tax
HMRC gives you a verification reference number for each subcontractor. You must keep this on file and include it in your CIS reporting when required.
Useful link: HMRC – Verify a subcontractor under CIS
Deduct the correct CIS tax at source
Once you know the subcontractor’s status, you must deduct CIS tax from their labour element before making payment (materials, VAT and certain other items may be excluded, depending on the invoice). The standard deduction rates are:
- 20% for verified, registered subcontractors
- 30% for unregistered or unverified subcontractors
- 0% for subcontractors with Gross Payment Status
These deductions are treated as advance payments towards the subcontractor’s own tax and (where relevant) National Insurance liability.
Pay the subcontractor the net amount
You then pay the subcontractor the agreed contract sum minus the CIS deduction. The deduction is not an extra cost to you as the contractor – you are simply withholding tax on HMRC’s behalf.
Example: If the labour element of an invoice is £2,000 and the subcontractor is on the standard 20% rate, you deduct £400 and pay £1,600 to the subcontractor. The £400 is passed to HMRC as CIS tax.
File the monthly CIS Return with HMRC
By the 19th of the following tax month, you must submit your CIS Return to HMRC. This can be done using HMRC’s online service or compatible commercial software. Your return must show for each subcontractor:
- Total payments made (usually the labour portion)
- Total CIS tax deducted
- Whether they were verified and any HMRC verification reference numbers
- Confirmation that you’ve considered employment status and are satisfied they are genuinely a subcontractor, not an employee
If you do not pay any subcontractors in a tax month, you must still file a nil return. HMRC’s system will generate late filing penalties if a return (including a nil one) is not received on time.
Useful link: HMRC – File your monthly CIS Return
Pay the CIS deductions over to HMRC
The CIS tax you deduct is then paid to HMRC, usually as part of your wider PAYE and NIC liability if you operate a payroll scheme. Payment deadlines are:
- By the 22nd of the following month if paying electronically
- By the 19th of the following month if paying by post
Missing payment deadlines can result in interest charges and penalties, even if the CIS Return itself was filed on time.
Tip: Set up calendar reminders for both the 19th (CIS filing) and the 22nd (PAYE/CIS payment) each month. Many contractors also use cloud accounting software that integrates CIS, automates deductions, and prepares CIS Returns for submission – significantly reducing admin time and the risk of human error.
CIS Return Deadlines
Staying on top of CIS deadlines is essential if you want to avoid unnecessary penalties and keep HMRC firmly onside. CIS operates on a strict monthly cycle, and even small delays can lead to escalating fines. Here are the two dates every contractor should have pinned to their calendar:
- Submission deadline: Your CIS Return must reach HMRC by the 19th of every month. Each return covers subcontractor payments made during the previous tax month (running from the 6th of one month to the 5th of the next).
- Payment deadline: Any CIS tax you deducted must be paid to HMRC by the 22nd of the following month if paying electronically, or by the 19th if making a postal payment. These payments are usually submitted alongside your PAYE and NIC liabilities.
Penalties for Late Filing
HMRC’s CIS penalty system is automatic, strict, and designed to escalate the longer a return remains unfiled. Even if you have no subcontractor payments to report, missing a submission triggers the same fines:
- 1 day late: £100
- 2 months late: £200
- 6 months late: £300 or 5% of the CIS deductions (whichever is higher)
- 12 months late: £300 or 5% of the CIS deductions (whichever is higher),
plus potential extra penalties of up to £3,000 for deliberate withholding or serious non-compliance
These penalties apply per return, meaning multiple missed months can add up quickly. Contractors who repeatedly file late may also find themselves subject to HMRC compliance checks.
Useful link: HMRC – CIS Penalties and Late Filing Rules
Tip: Always submit a nil return if you haven’t made any payments to subcontractors. HMRC doesn’t assume inactivity – without a filed return, the system still treats the month as overdue, and penalties are issued automatically.









