What is a CIS return, and does it actually apply to you? If you work in construction and get paid by a contractor rather than directly by a client, there’s a good chance you’re already inside the Construction Industry Scheme whether you realise it or not.

What Is the Construction Industry Scheme?

The Construction Industry Scheme (CIS) is HMRC’s system for collecting tax from people who work in construction. It applies to contractors who pay subcontractors for construction work, and it covers a wider range of jobs than most people expect. Site preparation, repairs, decorating, alterations and demolition all fall under the scheme, not just the big structural stuff.

Under CIS, a contractor deducts money from your payment before they hand it over. That deduction goes straight to HMRC as an advance payment toward your tax bill. The rate depends on whether you’re registered with HMRC: 20% if you are registered, 30% if you’re not. That’s a significant difference, which is why HMRC’s CIS 340 guidance is clear that subcontractors should register to avoid the higher rate.

What Does a Subcontractor Actually Need to Do Under CIS?

First, you should register with HMRC as a CIS subcontractor. This gets you the 20% deduction rate rather than 30%. If you haven’t done this yet and you’re currently being paid under CIS, it’s worth sorting out straight away. The extra 10% being held back by HMRC adds up fast.

After that, the main thing you need is to track the CIS deductions being made from your pay. Every contractor paying you under CIS should give you a CIS payment and deduction statement each month. You’ll need these statements when it comes to doing your Self Assessment tax return, because the deductions already paid to HMRC count as tax you’ve already handed over. Many subcontractors are owed a refund at the end of the year because more has been deducted than their actual tax liability.

What Happens If You Get It Wrong or Fall Behind?

Getting your CIS obligations wrong isn’t just an admin headache. Common CIS errors include being on the wrong deduction rate, having incorrect details on file with HMRC, or failing to submit returns on time. Penalties for CIS errors can reach up to £3,000, and HMRC does run pattern-based checks to spot inconsistencies.

If you’ve fallen behind, the honest answer is: it’s not as catastrophic as it feels at 11pm when you’re staring at a letter from HMRC. I’ve helped plenty of subcontractors get caught up on overdue returns and sort out their position with HMRC. The longer you leave it, the more it compounds, so dealing with it sooner is always the better option.

Do You Need an Accountant to Deal With CIS?

Technically, no. You can manage your CIS obligations yourself. But most of the subcontractors I speak to are on site all day and have no interest in learning the ins and outs of HMRC’s systems in their spare time. That’s a completely fair position. Your time earns you money on a job, not in front of a laptop filing returns.

What an accountant actually does for you here is make sure you’re on the right deduction rate, that your Self Assessment picks up every CIS deduction you’ve paid, and that you’re not leaving a refund on the table. A lot of subcontractors don’t realise they’re owed money back until someone actually looks at the numbers properly.