CIS monthly return deadline (19th of the month)

Under the Construction Industry Scheme (CIS), contractors must file a monthly return with HMRC by the 19th of the month following the end of the tax month — even when no payments have been made to subcontractors.

What is this filing?

The CIS monthly return (form CIS300) reports payments made to subcontractors and the tax deducted under CIS. Tax months run from the 6th of one month to the 5th of the next.

When is it due?

19th of the month following the tax month end. Nil returns must still be filed when no subcontractors were paid. Online filing is mandatory.

What's the penalty for missing it?

Late return: £100 (1 day late), additional £200 (2 months late), 5% of CIS tax or £300 (6 months late), same again at 12 months. Nil-return failures attract the same flat penalties.

What it actually costs

The CIS late-return penalty starts at £100 for a single day late. At two months it doubles to a further £200, making the total £300. At six months HMRC levies 5% of the CIS tax shown on the return (or £300, whichever is higher), and the same again at twelve months. For a contractor with several subcontractors and meaningful deductions, the six-month and twelve-month penalties quickly exceed the flat-rate amounts. Nil-return penalties follow the same schedule even though there was no tax deducted.

Why this catches practices out

• Contractors with seasonal work often assume they do not need to file a nil return in quiet months — the £100 penalty applies regardless.
• A business that switches from being a subcontractor to engaging subcontractors becomes a contractor and may not realise the monthly filing duty has started.
• CIS deductions must be paid to HMRC by the 22nd of the month — a separate deadline from the 19th return filing date that catches some contractors out.

How PenaltyProof helps

PenaltyProof's CIS monitoring (paid plans, opt-in) emails reminders for each monthly 19th deadline. Opt in once per practice; reminders fire for every applicable client.

Frequently asked questions

Must a nil return be filed when no subcontractors were paid?

Yes. A CIS contractor with no payments in a month must still file a nil return or notify HMRC of inactivity by the 19th. Failing to do so incurs the same penalty as failing to file a return with payments.

What counts as a 'tax month' for CIS purposes?

CIS tax months run from the 6th of one calendar month to the 5th of the following month, mirroring the PAYE tax month. The return covers the month ended 5th and is due by the 19th of the same calendar month the period ends.

Can a contractor be both a CIS contractor and a subcontractor?

Yes. A business that engages subcontractors and is itself engaged by a higher-tier contractor is both at once. It files a CIS monthly return as a contractor and provides its gross payment or deduction to the engaging contractor as a subcontractor.

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