Monthly CIS Returns (CIS300)

Key facts

CIS returns must be filed monthly — by the 19th of the month following the tax month.
The return covers all payments and deductions for the tax month (6th to 5th).
Returns must be filed online — paper returns are no longer accepted.
You must file a return even if you made no subcontractor payments (a “nil return”).
Include all subcontractors paid in the period, including those with gross payment status.

What Is the Monthly CIS Return?

The monthly CIS return (form CIS300) is the mechanism by which contractors report their subcontractor payments and CIS deductions to HMRC. Every CIS contractor must file a return for each tax month, regardless of whether any payments were made.^[1]

The return serves several purposes:

It tells HMRC how much you have deducted from subcontractors and should be paying over
It gives HMRC the data to match deductions to individual subcontractors’ tax records
It enables subcontractors to claim credit for CIS deductions suffered on their own tax returns

What to Include on the Return

For each subcontractor you paid during the tax month, the CIS300 return requires:^[1]

Field	What to Enter
Subcontractor name	Full legal name (must match HMRC records)
Unique Taxpayer Reference (UTR)	The subcontractor’s 10-digit UTR
Verification number	The reference number HMRC provided when you verified the subcontractor
Total payment	The gross amount paid (excluding VAT), before deductions
Cost of materials	Qualifying materials purchased by the subcontractor for the work
CIS deduction	The amount deducted (total payment minus materials, times the deduction rate)

You also need to declare whether you have employed any new subcontractors in the period, and provide a declaration that the information is correct.

Gross payment subcontractors: You must include subcontractors with gross payment status on your return, even though no deduction was made. Report the full payment and £0 deduction. This is important for HMRC’s records and the subcontractor’s annual review.

Understanding Tax Months

CIS tax months do not align with calendar months. Each tax month runs from the 6th of one month to the 5th of the next:^[2]

Tax Month	Period	Return Deadline
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

Payments made on the 5th of a month fall in the preceding tax month, while payments made on the 6th fall in the following tax month. Getting this boundary right is essential for correct reporting.

How to File

CIS returns must be filed online. Paper returns are no longer accepted. You can file through:^[1]

1. HMRC Online Services

Sign in to your HMRC business tax account
Select Construction Industry Scheme
Choose “File a return” and select the tax month
Enter the details for each subcontractor
Review and submit the return

2. Commercial Software

Many payroll and accounting software packages can file CIS returns directly with HMRC via their APIs. This is more efficient for contractors with multiple subcontractors, as data can be entered during the month and submitted in bulk.

The Contractor’s Declaration

Each CIS return includes a declaration that the contractor must complete. The declaration includes confirming:^[3]

The employment status of all workers has been considered
Workers treated as subcontractors under CIS are not employees
The information on the return is correct and complete

Employment status declaration: This declaration is important. By filing the CIS return, you are confirming that you have considered whether each worker is genuinely self-employed. If HMRC later determines that a “subcontractor” was actually an employee, you could face PAYE, NIC, and penalty liabilities.

Periods of Inactivity

If you anticipate no subcontractor payments for an extended period, you can request HMRC to make your CIS scheme “inactive.” This temporarily suspends the requirement to file monthly returns. However:

You must contact HMRC to request inactivity
You must reactivate your scheme before making any new subcontractor payments
If you do not request inactivity, you must continue filing nil returns every month

Record-Keeping for Returns

Keep a copy of every CIS return filed, along with the supporting information (subcontractor details, payment records, materials evidence, verification references). Records must be retained for 3 years after the end of the tax year to which they relate.^[2]

Frequently Asked Questions

What is a CIS300 form?

The CIS300 is the monthly return that CIS contractors must file with HMRC. It lists all subcontractors paid during the tax month, the gross amount paid to each, any materials costs, and the CIS deductions made. It is filed online through HMRC’s business tax services.

When is the CIS return due?

The CIS return for each tax month (6th to 5th) must be filed by the 19th of the following month. For example, the return for the period 6 April to 5 May is due by 19 May. Late filing attracts penalties.

Do I need to file a return if I made no payments?

Yes. If you are registered as a CIS contractor but did not make any payments to subcontractors in a tax month, you must still file a nil return. Failure to file a nil return attracts the same penalties as a late return.

Can I file CIS returns using software?

Yes. You can file CIS returns directly through HMRC’s online services, or use commercial payroll/CIS software that connects to HMRC via APIs. Most accounting software packages that support CIS can file returns electronically.

Sources

File your CIS monthly return — GOV.UK
What you must do as a CIS contractor — GOV.UK
CIS: monthly return (CISR46000) — HMRC