- What Is a CIS Monthly Return?
- What Do You Actually Need to Report?
- A Real Example
- Don’t Forget the Bigger Picture
- What Happens If You Get It Wrong?
- One Thing You Can Do Today
CIS Monthly Returns: What Every UK Construction Contractor Needs to Know
It’s the 19th of the month. You’ve been on site since 7am, your phone hasn’t stopped, and somewhere in the back of your mind you know there’s a CIS return due. Sound familiar?
If you’re a contractor under the Construction Industry Scheme, missing that deadline isn’t just annoying — it can cost you money. And a lot of contractors get this wrong, not because they don’t care, but because nobody ever sat them down and explained it properly.
So let’s fix that.
What Is a CIS Monthly Return?
If you pay subcontractors for construction work, HMRC classes you as a contractor under CIS. That means every single month, you must tell HMRC what you’ve paid your subbies and how much tax you’ve deducted.
This is your CIS monthly return. It’s not optional. It’s not something you do when you get round to it.
The deadline is the 19th of every month, covering the previous tax month. Miss it, and you’re looking at automatic penalties starting at £100. Miss it for a few months and those fines stack up fast.
What Do You Actually Need to Report?
For each subcontractor you’ve paid, you need to include:
- Their name and UTR (Unique Taxpayer Reference)
- The total amount paid
- The amount of CIS deduction you’ve made
The deduction rate depends on their verification status. Subcontractors who are verified with HMRC get deducted at 20%. Unverified subbies? You’re deducting 30%. And if you haven’t verified them at all, you could be in serious trouble.
A Real Example
Say you run a small groundworks business and you’ve got three subbies on site this month. One is fully registered under CIS with gross payment status — so you pay them in full, no deduction. One is verified at 20%. And one you took on last week and haven’t verified yet.
That last one? You must deduct 30% from the labour element of their payment and hand it over to HMRC. You can’t just pay them and sort it later. HMRC expects that money on time, reported on time.
And here’s the bit people miss — even if you paid no subcontractors that month, you still need to submit a nil return. No exceptions.
Don’t Forget the Bigger Picture
CIS doesn’t exist in isolation. If you’re VAT-registered and working with other VAT-registered businesses in the supply chain, the VAT reverse charge applies to most construction services. That affects your cash flow more than you might think.
And if you’re using workers who look like subcontractors but work like employees, IR35 is something you need to think about too. Getting that wrong can mean back-tax, interest and penalties — all at once.
What Happens If You Get It Wrong?
HMRC can charge you the full amount of CIS deductions you should have made, even if you already paid the subcontractor in full. That means you could end up paying twice. Plus interest. Plus penalties.
It’s not a grey area. It’s a straightforward scheme with straightforward rules — but only if you’re on top of it.
One Thing You Can Do Today
Pull up your subcontractor list right now. Check every single one is verified with HMRC. If they’re not, call HMRC’s CIS helpline or log in to your HMRC account and verify them today.
That one step protects you from the 30% deduction risk and keeps your returns clean.
Not sure how this affects your construction business? Book your free 20-minute call with Magnum Accountancy today: https://magnumaccountancy.com/book-a-free-call
Not sure how this affects your construction business?
Book Your Free 20-Min Call