The CIS monthly return should be submitted such that it is received by HMRC 14 days after the month end. Therefore a return for the month ended 5 January 2018 should be with HMRC no later than 19 January 2018.
The current list of penalties is as follows:
•a return submitted late – £100
•a return submitted two months late – another £200
•a return submitted six months late – another £300 or 5% of the deductions, whichever is greater
•a return submitted twelve months late – another £300 or 5% of the deductions, whichever is greater.