CIS Return: A Contractor’s Guide to Filing, Deadlines and the 2026 Rule Changes

A CIS Return is the monthly report a contractor submits to HMRC listing every payment made to subcontractors under the Construction Industry Scheme, along with the tax deducted from each one. It’s due by the 19th of the month following the tax period it covers. Since 6 April 2026, a return is required for every tax month, including ones with no subcontractor payments at all.

Picture a small groundworks contractor in St Albans Hertfordshire who pays four or five subcontractors most months but goes quiet every February while waiting on the next job to start. For years, the assumption was simple: no payments, nothing to send. That assumption now carries a £100 penalty. HMRC tightened the nil return rule from 6 April 2026 as part of the wider CIS reforms confirmed at Autumn Budget 2025, and it’s just one of several changes reshaping how contractors handle CIS Returns this year alongside new penalties that can now reach a company director personally, not just the business.

This guide walks through what a CIS Return is, who has to file one, what it must contain, and the deadlines, deductions and penalties contractors need to build into their monthly routine.

What Is a CIS Return?

A CIS Monthly Return is the document contractors send HMRC to report payments made to subcontractors for construction work and the tax withheld from those payments under the Construction Industry Scheme.

The scheme exists to stop tax being lost in a sector where subcontractors have historically been paid cash-in-hand or gone unregistered, so contractors deduct tax at source and pass it to HMRC on the subcontractor’s behalf, similar in spirit to PAYE.

Each CIS Monthly Return covers one tax month, which runs from the 6th of one calendar month to the 5th of the next not a standard calendar month. So, the return covering 6 April to 5 May reports everything paid in that window, and nothing else.

Who Must File a CIS Return?

Any business or individual registered as a contractor under the Construction Industry Scheme must file a CIS Return companies, partnerships and sole traders included, provided they pay subcontractors for construction work. This also captures deemed contractors: businesses outside construction (property developers, some large retailers) that spend heavily enough on construction work to fall under the scheme’s rules.

Subcontractors, by contrast, don’t file monthly CIS Returns themselves. Their CIS deductions are reconciled through their own annual Self Assessment.

Filing responsibility doesn’t pause just because a contractor is between subcontractors. The obligation is monthly and ongoing for as long as the CIS registration is active, which is precisely why the 2026 nil return change (covered below) has caught so many businesses out.

What a CIS Return Must Include

Each CIS Return must list every subcontractor paid in that tax month, with:

• The subcontractor’s name and Unique Taxpayer Reference (UTR)
• Their National Insurance number (sole traders) or company registration number
• The verification number HMRC issued when the subcontractor was checked
• The gross payment made, excluding VAT
• Any materials deduction applied before tax was calculated
• The amount deducted and sent to HMRC

CIS Contractors also have a separate duty to give each subcontractor a monthly payment and deduction statement confirming what was paid and withheld, so the subcontractor can reconcile it against their own tax return.

How to File a CIS Return

1. Register as a contractor with HMRC before you first pay a subcontractor.
2. Verify each new subcontractor with HMRC to get their correct deduction rate.
3. Log every payment made during the tax month, with the gross amount, materials deducted and tax withheld.
4. Submit the CIS300 return online through the Government Gateway, or through CIS-capable commercial software, by the 19th.
5. Pay the deducted tax to HMRC by the 22nd if paying electronically, or the 19th by post.
6. Issue each subcontractor their monthly payment and deduction statement.

CIS Deduction Rates and Verification

Before a subcontractor is paid for the first time, the contractor must verify them with HMRC, which confirms which of three deduction rates applies:

Once verified, a subcontractor only needs re-verifying if the contractor hasn’t paid them at all within the current or two previous tax years. Deduction rates apply to the labour element of a payment only genuine materials costs the subcontractor paid for directly are excluded before the percentage is applied. HMRC, not the contractor, decides which rate applies during verification, which means guessing or applying a “safe” rate isn’t an option the return has to match what verification returned.

Worked example

A registered subcontractor invoices £1,000 for a job, of which £200 is materials they paid for directly. The labour element is £800. At the standard 20% rate, the contractor deducts £160 and pays the subcontractor £840, then sends the £160 to HMRC.

Gross payment status lets subcontractors receive full payment with no deduction at all, in exchange for passing HMRC’s three qualifying tests: the business test, the turnover test and the compliance test. It’s a valuable status to hold, which is exactly why the 2026 fraud rules (below) treat losing it as a serious penalty in its own right.

Filing and Payment Deadlines

The CIS Return deadline is fixed at the 19th of every month, covering the tax month that ended on the 5th. Payment of the deducted tax follows shortly after: the 19th by post or the 22nd if paid electronically. Neither date moves for weekends or bank holidays, and there’s no grace period. A return filed even one day late attracts the same penalty as one filed a month late.

A practical routine most accountants recommend:

• Set an internal target of the 15th, giving a buffer for verification queries or correcting figures
• File online through the Government Gateway, which gives an automatic confirmation receipt
• Keep CIS records including verification numbers and deduction statements for at least three years after the tax year they relate to, in case HMRC asks to see them

The 2026 Nil Return Reform

From 6 April 2026, HMRC removed the informal tolerance that let contractors do nothing in a month with no subcontractor payments. Contractors must now either file a nil return or submit an inactivity request at least 14 days before the quiet period begins, which can cover up to six months. Missing a nil return trigger exactly the same escalating penalties as missing a return with real payment data on it.

The same reform package simplified CIS in one useful respect: payments to local authorities and certain public bodies are now exempt from CIS deductions altogether, cutting a layer of unnecessary admin for contractors who work with the public sector.

Director Liability and Fraud Connection Rules

The most significant change in 2026 isn’t really about the CIS Return form itself it’s about who can be held liable for what’s on it. HMRC gained new powers, confirmed at Autumn Budget 2025 and legislated by amending Part 3 Chapter 3 of the Finance Act 2004 and the Income Tax (Construction Industry Scheme) Regulations 2005. The new powers are modelled on the existing VAT “Kittel” fraud test, aimed at tackling organised fraud in construction supply chains.

Under the new rules, if a contractor knew or should have known that a payment or credit was connected to fraudulent tax evasion anywhere in their supply chain, HMRC can:

• Immediately cancel the business’s gross payment status, with no prior notice
• Make the business liable for the lost tax, even if the business itself filed correctly
• Charge a penalty of up to 30% of the lost tax and this penalty can be levied not just on the business but personally on its directors and other connected persons

Reapplying for gross payment status after it’s cancelled under these rules now takes five years, up from one. HMRC expects the measures to recover roughly £205 million in their first year, and has said data-matching between CIS returns and wider tax records will pick out mismatches automatically. For contractors, the practical upshot is straightforward: due diligence on subcontractors has moved from good practice to a genuine legal safeguard. That means checking registration history, ownership changes and payment patterns, not just verifying a UTR.

CIS Return Penalties

Late CIS Returns escalate quickly, with no warning period before the first charge lands:

Contractors who believe a penalty was issued in error have 30 days to appeal, either online or in writing appeals can’t be made by phone. HMRC can reduce or cancel penalties in genuine cases of illness or unavoidable disruption, but this has to be argued formally rather than assumed.

Common Compliance Failures

The failures that generate most CIS penalties are avoidable rather than dramatic:

• Treating quiet months as exempt: since April 2026, a nil return has to be actively filed, not skipped
• Skipping verification: before a first payment, defaulting a subcontractor to the 30% rate unnecessarily
• Entering rounding errors or negative figures: which HMRC’s system rejects and flags for correction
• Filing on the 19th itself: rather than earlier, leaving no buffer if a system issue or last-minute query crops up
• Assuming an accounting package alone is protection: software will calculate and submit a CIS Return correctly, but it won’t demonstrate the due diligence HMRC now expects on subcontractor fraud risk

Conclusion

The CIS Return itself hasn’t changed shape in 2026 it’s still a monthly list of subcontractor payments and deductions, due on the 19th. What’s changed is the cost of getting it wrong: nil months now need filing, unverified fraud risk in the supply chain can strip a business of gross payment status overnight, and directors can carry personal liability for the first time.

Building a monthly CIS routine verify before paying, file before the 15th, and check who’s really in the supply chain is now the difference between routine admin and a costly HMRC investigation.

If your CIS process still relies on a quick verification check, have Julian Hobbs & Co. review your due-diligence trail before your next filing deadline. If you’re managing CIS Returns for multiple subcontractors each month, speak to a specialist CIS accountant to check your verification and due-diligence processes meet the 2026 standard before your next filing deadline.

FAQs: Frequently Asked Questions