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CIS Monthly Returns: What Contractors Must Submit and When

Complete guide to CIS monthly returns for 2026/27: deadlines, what to submit, penalties for late filing, and how contractors stay compliant. Expert advice from YRF Accountants, Bolton & Manchester.

Call 01204 938696 or email info@yrfaccountants.com

CIS Monthly Returns: What Contractors Must Submit and When

Once you are registered as a CIS contractor, the work does not stop there. Every tax month, HMRC requires a CIS monthly return detailing every payment made to subcontractors, the deductions withheld, and confirmation of employment status. Missing this deadline, even by a few days, triggers automatic penalties.

This guide explains exactly what a CIS monthly return must include, when it is due, and how to avoid the penalties that catch out so many construction businesses. YRF Accountants manage monthly CIS returns for contractors across Bolton, Manchester, and Bury, so nothing slips through the net.

What Is a CIS Monthly Return?

A CIS monthly return, officially known as a CIS300, is the report every registered contractor must file with HMRC each tax month. It confirms how much you paid for each subcontractor, how much CIS tax you deducted, and that you have correctly assessed their employment status.

You must file a return even in months where you did not pay any subcontractors. This is known as a "nil return" and is one of the most missed obligations among smaller construction businesses.

What You Must Submit on Your CIS300 Return

Each monthly return must include the following information for every subcontractor paid during that tax month:

What to Include	Detail
Subcontractor Details	Name, UTR, and verification reference for each subcontractor paid that month
Gross Amount Paid	Total payment made before any CIS deduction, excluding VAT
Cost of Materials	Materials element of the payment, which is excluded from the CIS deduction
CIS Deduction Made	Tax withheld at 0%, 20%, or 30% depending on subcontractor status
Nil Return Declaration	Required even if no subcontractors were paid that month
Employment Status Declaration	Confirmation that none of the subcontractors should be treated as employees
Contractor UTR & Accounts Office Reference	Used by HMRC to match the return to your contractor record

CIS Monthly Return Deadlines for 2026/27

CIS tax months do not align with calendar months. Each tax month runs from the 6th to the 5th, and your return and any tax due must reach HMRC by the 19th following the end of that period. Key dates to plan around:

Tax Month	Period Covered	Return & Payment Due By
Month 1	6 April – 5 May	19 May
Month 2	6 May – 5 June	19 June
Month 3	6 June – 5 July	19 July
Month 6	6 September – 5 October	19 October
Month 9	6 December – 5 January	19 January
Month 12	6 March – 5 April	19 April

Missing even one of these deadlines even by a single day triggers an automatic HMRC penalty, so it is worth building return preparation into your monthly bookkeeping routine rather than leaving it until the 19th.

Penalties for Late or Missing CIS Returns

HMRC applies escalating, automatic penalties for late or missing CIS monthly returns, regardless of whether any subcontractors were actually paid that month:

£100 fixed penalty for a return up to 1 month late

£200 additional penalty for a return 2 months late

Higher of £300 or 5% of CIS deductions for returns 6 months late

A further penalty of the same amount, or higher, for returns 12 months late

Daily penalties may also apply for prolonged non-compliance

These penalties accumulate per return, so a contractor who misses several consecutive months can quickly face penalties running into thousands of pounds, even before any underlying CIS deductions are corrected.

How to Submit Your CIS Monthly Return

Most contractors submit CIS300 returns online via their HMRC business tax account, though commercial payroll and CIS software can also file directly. Before submitting, you must verify each new subcontractor with HMRC to confirm the correct deduction rate. If you have not yet completed contractor registration, our guide to

How to Register as a CIS Contractor with HMRC walks through the registration process step by step.

Many contractors choose to hand this over to a specialist accountant, particularly once they are managing multiple subcontractors across several active sites, where verification, deduction calculations, and statement issuing become time-consuming each month.

Our Compliance Services cover monthly CIS300 submissions, subcontractor verification, and HMRC liaison, so your returns are filed correctly and on time, every month.

Common Mistakes That Lead to Penalties

Most CIS return penalties stem from avoidable errors rather than genuine non-compliance:

Forgetting to file a nil return in months with no subcontractor payments

Incorrectly including materials costs within the deduction calculation

Failing to verify new subcontractors before the first payment

Missing the 19th deadline due to manual, last-minute preparation

Not issuing payment and deduction statements to subcontractors

Building monthly CIS preparation into your existing bookkeeping cycle, ideally alongside payroll, removes most of this risk entirely.

Never miss another CIS deadline. YRF Accountants handles monthly CIS300 returns for contractors across Bolton and Manchester, on time, every month.

Book a Free CIS Compliance Call

Frequently Asked Questions: CIS Monthly Returns

What is a CIS monthly return?	A CIS monthly return (CIS300) is a report contractors must submit to HMRC every tax month, detailing payments made to subcontractors, deductions withheld, and confirmation that none of the subcontractors should be treated as employees.
When is the CIS monthly return deadline?	CIS returns and any tax due must reach HMRC by the 19th of every month, covering payments made in the previous tax month (which runs from the 6th to the 5th).
Do I need to submit a CIS return if I paid no subcontractors that month?	Yes. You must submit a nil return even if you made no subcontractor payments during that tax month, otherwise HMRC may apply a late filing penalty.
What happens if I submit my CIS return late?	HMRC applies automatic penalties starting at £100 for a return up to one month late, rising to £200, then the higher of £300 or 5% of deductions for returns six months late, with further penalties at twelve months.
Can I submit CIS returns online?	Yes. Most contractors submit CIS300 returns via HMRC's online service or through commercial payroll and CIS software. Accountants can also file on your behalf using agent access.
What information do I need for each subcontractor on the return?	You need their name, UTR, verification reference, gross payment amount, cost of materials excluded from deduction, and the CIS deduction withheld at the applicable rate.
Can YRF Accountants handle my monthly CIS returns for me?	Yes. YRF Accountants manages monthly CIS300 submissions, subcontractor verification, and deduction statements for contractors across Bolton, Manchester and Bury, ensuring deadlines are never missed.