Working as a contractor in the construction industry is a great way to enjoy some of the benefits of working for yourself, such as a higher degree of freedom to choose when, and for whom, you work.

However, there’s one essential task construction industry contractors can’t escape and need to stay on top of constantly, if they want to avoid HMRC penalties - keeping up with monthly CIS returns. 

Under the Construction Industry Scheme (CIS), contractors must file a monthly return showing payments made to subcontractors and any tax deducted.

It may sound straightforward enough, but it’s all too easy to miss a deadline when you’re busy running projects or managing payments. The CIS return deadline rolls around every month, and missing it (even by a day) can cost you.

So, in order to help our existing and future construction contractor clients, we’ll explain when the CIS return deadline falls, what happens if you file late, and how to make the whole process quicker and easier.

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What is the CIS return deadline?

The CIS return deadline is the 19th of every month, and it covers the payments you made to subcontractors in the previous tax month. A tax month runs from the 6th of one month to the 5th of the next.

So, for example:

If you made payments to subcontractors between 6th September and 5th October, your CIS return must be submitted by 19th October.

This monthly cycle repeats throughout the year, even if you haven’t paid any subcontractors during that period you’ll still need to submit what’s called a ‘nil return’ to stay compliant with HMRC rules.

Sticking to these dates is paramount. HMRC’s system is strict, and even a short delay can trigger an automatic penalty (we’ll explain how those work later).
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How to file your CIS return

Filing your CIS return isn’t necessarily complicated, but it is important that it’s accurate and on time. You have two main options for submitting it:

1. Through HMRC’s online services‍

You can log in to your Government Gateway account and file your CIS return directly.

2. Through accounting software‍

Many contractors use accounting software (like Crunch!) that automatically generates and submits CIS returns, saving time and reducing the risk of mistakes.
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When filing, you’ll need to include:

When you’re ready to submit your CIS return, make sure you’ve got all the right details to hand.

HMRC will expect to see:

• Each subcontractor’s name, Unique Taxpayer Reference (UTR), and CIS verification number
  
  
• The total amount paid to each subcontractor during the tax month (excluding VAT)
  
  
• Any CIS deductions you’ve made – but leave out the cost of materials
  
  
• A quick confirmation that you’ve verified each subcontractor’s status with HMRC

It’s worth keeping everything tidy (invoices, verification checks, deduction calculations) for at least three years in case HMRC ever needs to see them. If you spot an error after submitting, you can log in to your HMRC account and amend your return easily.

If you use a digital accounting platform, it can handle much of this automatically, helping you meet every CIS return deadline without stress. This also helps if you ever need to claim a CIS deduction refund.

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What happens if you miss the CIS return deadline?

If you miss the CIS return deadline HMRC automatically issues a penalty, even if you didn’t have any payments to report. The longer your return is late, the higher the fine becomes:

It can add up fast, especially if you forget more than once.

If you’ve missed a deadline for a genuine reason — for example, due to illness, a technical issue, or circumstances beyond your control — you can appeal the penalty and explain your situation to HMRC.

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How to stay on top of your CIS returns (and avoid penalties)

Staying organised is the best way to keep HMRC happy and avoid unnecessary stress. You can do this by setting monthly reminders of the CIS return deadline which always falls on the 19th. So add it to your calendar and set a recurring alert.

Also keeping good records, by recording subcontractor payments and deductions as you go, will make filing faster. And smart accounting software, like ours for example,  can take care of your CIS returns automatically, from tracking payments to submitting returns on time every month.

Once you have a , meeting your CIS return deadline becomes one less thing to worry about,  giving you more time to focus on running your business.

If you’d like to make CIS compliance simple and stress-free, get in touch with Crunch today to see how our software and expert team can help.

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