19th of every month: CIS monthly return
Contractors under the Construction Industry Scheme must file the CIS300 return for each tax month by the 19th of the following month, and pay the deductions by the 22nd.
Who it applies to
Any business that pays subcontractors for construction work, and any business outside construction that spends more than £3 million a year on it.
What has to happen
The return lists every subcontractor paid in the month, the amounts and the deductions made. A nil return is still due for a month with no payments, unless you have told HMRC you have stopped paying subcontractors.
If you miss it
£100 for a return one day late, £200 at two months, then £300 or 5% of the deductions at six months and again at twelve months. Source: gov.uk and Companies House guidance, checked September 2026.
What to do
Verify every new subcontractor with HMRC before the first payment; the rate to deduct depends on it.
