How do I file monthly CIS returns?

Learn how to file monthly CIS returns correctly and on time. Understand what information you need to include, when to file, and how to avoid penalties from HMRC.

If you run a construction business and pay subcontractors, you must file monthly returns under the Construction Industry Scheme (CIS). These returns tell HMRC how much you have paid to subcontractors and how much tax you have deducted from their payments.

Submitting your CIS returns accurately and on time is essential to stay compliant and avoid penalties. Although the process may seem complex at first, it becomes straightforward once you understand the steps.

This article explains how to file your monthly CIS returns, what information you need, and how to prevent common mistakes.

What is a CIS return?

A CIS return is a monthly report that contractors submit to HMRC detailing all payments made to subcontractors during the previous tax month. It also confirms the amount of CIS tax deducted and paid to HMRC.

The return applies to all contractors registered under the Construction Industry Scheme, including:

  • Construction companies and sole traders who hire subcontractors.

  • Property developers who manage construction work.

  • Businesses spending more than £3 million a year on construction.

If you are a subcontractor only, you do not need to file CIS returns — your contractor does this for you.

When to file CIS returns

CIS returns must be filed by the 19th of each month, covering the tax month that ended on the 5th.

For example:

  • A return for work done between 6 April and 5 May must be submitted by 19 May.

Even if you have not paid any subcontractors during the month, you must still file a nil return to let HMRC know. Missing a return, even a nil one, can result in automatic penalties.

Information you need to file a CIS return

Before submitting your return, make sure you have:

  • The subcontractor’s name and Unique Taxpayer Reference (UTR).

  • Their verification number from HMRC (proving they are registered).

  • The total amount paid to each subcontractor.

  • The amount of CIS tax deducted (if applicable).

  • Details of any subcontractors verified as gross payment (no deductions).

Keeping accurate payment records throughout the month will make this process much easier.

How to file your monthly CIS return

You can file CIS returns online using HMRC’s portal or through accounting software.

Option 1: File using HMRC’s online service

  1. Log in to your HMRC Government Gateway account.

  2. Go to the Construction Industry Scheme section.

  3. Select “File a monthly return.”

  4. Enter the required details for each subcontractor.

  5. Review and confirm your submission.

  6. HMRC will issue a confirmation receipt once your return is submitted successfully.

Option 2: File using accounting or payroll software

Many accounting packages, such as Xero, QuickBooks, or Sage, allow you to file CIS returns directly.

  • Enter your subcontractor payments into the software during the month.

  • The system automatically calculates CIS deductions and generates the return.

  • Review the information and submit electronically to HMRC through the software.

This method saves time and reduces the risk of manual entry errors.

Submitting nil returns

If you have not paid any subcontractors in a month, you must still submit a nil return.

You can do this through:

  • Your HMRC online account (by selecting “Nil return”).

  • Your accounting software if it supports CIS.

  • The HMRC CIS helpline by phone.

Failure to submit a nil return by the 19th of the month will still result in a late filing penalty.

Paying CIS deductions to HMRC

After filing your return, you must pay any CIS tax deductions to HMRC by the 22nd of the month (or the 19th if paying by post).

Payments can be made:

  • By bank transfer or direct debit through your HMRC account.

  • By using your Accounts Office reference number on all payments.

Timely payment ensures you remain compliant and avoid interest or penalties.

Penalties for late or incorrect returns

HMRC automatically issues penalties for late CIS returns:

  • 1 day late: £100 fixed penalty.

  • 2 months late: £200 fixed penalty.

  • 6 months late: £300 or 5% of the CIS deductions, whichever is higher.

  • 12 months late: £300 or 5% of the CIS deductions, whichever is higher (further fines may apply for deliberate errors).

You can appeal if you have a valid reason for missing the deadline, such as illness or technical issues.

Common CIS return mistakes

Avoid these common errors to keep your records clean and prevent penalties:

  • Forgetting to file a nil return.

  • Entering incorrect subcontractor details or UTRs.

  • Failing to verify new subcontractors before payment.

  • Misreporting payments or deduction amounts.

  • Paying subcontractors before checking their CIS status.

Double-check all details before submission to ensure your return is accurate.

How to correct an error

If you realise you have made a mistake after submitting a CIS return, you can file an amended return through your HMRC account or software.

When correcting a return:

  • Select the same month and update the incorrect information.

  • HMRC will automatically replace the previous return with the updated one.

If you are unsure what to amend, contact HMRC or your accountant for guidance.

How an accountant can help with CIS returns

Managing CIS can be time consuming, especially when balancing payroll, invoices, and tax deadlines. An accountant experienced in CIS can help by:

  • Registering your business for CIS.

  • Verifying subcontractors correctly.

  • Calculating CIS deductions and producing monthly returns.

  • Submitting returns to HMRC on your behalf.

  • Managing CIS payments and avoiding penalties.

  • Advising on record keeping and compliance.

Outsourcing CIS management ensures accuracy, saves time, and keeps your business compliant with HMRC rules.

The bottom line

Filing CIS returns is a key responsibility for contractors in the construction industry. Returns must be submitted by the 19th of each month, even if you have not paid any subcontractors.

You can file online through HMRC or use accounting software to simplify the process. Always verify subcontractors, keep accurate records, and make payments to HMRC on time to avoid penalties.

Working with a qualified accountant ensures your CIS obligations are met accurately, freeing you to focus on managing projects and growing your construction business.