Understanding CIS: What Contractors Must Know
If you work in the UK construction industry, chances are you’ve heard of the Construction Industry Scheme (CIS). But even experienced contractors can get tripped up by the rules — and mistakes can lead to costly fines, cash flow issues, or strained relationships with subcontractors.
This guide breaks down the essentials of CIS for contractors, and highlights key points you need to stay compliant and in control.
What is CIS?
CIS is a tax deduction scheme set up by HMRC to ensure tax is collected from payments made to subcontractors working in construction. Under CIS, contractors deduct money from a subcontractor’s payments and pass it to HMRC. These deductions count as advance payments toward the subcontractor’s tax and National Insurance.
You must register as a contractor with HMRC if you:
- Pay subcontractors for construction work
- Spend more than £3 million on construction within a 12-month period (even if it’s not your main business)
Your Responsibilities as a Contractor
If you’re a contractor under CIS, you’re responsible for:
- Registering with HMRC as a CIS contractor
- Verifying subcontractors with HMRC before you pay them
- Deducting the correct amount (typically 20% or 30%)
- Submitting monthly CIS returns
- Providing payment & deduction statements to each subcontractor
- Paying HMRC on time
Missing any of these steps can result in penalties — even if the mistake was accidental.
Common Mistakes (and How to Avoid Them)
1. Not Verifying Subcontractors Properly
Before paying a subcontractor, you must verify them with HMRC to confirm their tax status. Failing to do this could mean deducting the wrong amount — or not deducting when you should.
✅ Tip: Use HMRC’s online CIS system or ask your accountant to verify subcontractors on your behalf.
2. Forgetting Monthly Returns
CIS returns must be submitted by the 19th of each month following the payment. Even if no payments were made, you still need to submit a nil return — or face a fine.
✅ Tip: Set calendar reminders or use accounting software that integrates with CIS to automate reminders.
3. Confusion Over What Qualifies as Construction Work
Not all payments to workers fall under CIS. For example, work like architecture or scaffolding hire without labour may be excluded. But supply-and-fit contracts often are included.
✅ Tip: When in doubt, check HMRC’s CIS guidance or consult a specialist accountant.
How We Help Contractors Stay Compliant
At AXT Accountants, we work with construction firms of all sizes — from local builders to national developers — to manage their CIS obligations with confidence.
We offer:
- Contractor and subcontractor registration
- Monthly CIS return filing
- Payment & deduction statement generation
- Liaising with HMRC on your behalf
This allows you to stay focused on site while we handle the paperwork.
Final Word
CIS isn’t just a box-ticking exercise — it affects your subcontractors, your taxes, and your bottom line. The good news? With the right systems and support in place, it doesn’t have to be a headache.