Let me ask you something first. If you’re working in construction and someone’s mentioned “CIS” to you without properly explaining it, has anyone actually walked you through what it means for your money, month to month?
Because in my experience at MSK Accountants in Preston, most people in the trade have a rough idea that CIS involves tax being taken off their pay, but genuinely don’t understand the mechanics of why it happens, how much, or how they get any of it back. So let’s go through this properly, top to bottom, so you’ve got the full picture and aren’t left needing to search for the missing pieces afterwards.
What Is CIS, Actually?
CIS stands for the Construction Industry Scheme. It’s HMRC’s system for collecting tax from people working in construction, but instead of you paying it directly like a typical self-employed person, the money gets deducted before it even reaches you.
Here’s the basic mechanism. If you’re a contractor paying a subcontractor for construction work, you’re legally required to deduct money from that payment and send it straight to HMRC, rather than paying the subcontractor the full amount. The subcontractor then gets credit for that deduction against their eventual tax bill.
It exists because construction has historically had a problem with people disappearing without paying tax owed. CIS is HMRC’s way of collecting tax upfront, spread across the year, rather than relying entirely on people declaring everything honestly come January.
Contractor or Subcontractor Which Are You?
This distinction matters enormously, because your obligations under CIS are completely different depending on which role you’re in.
Contractors pay subcontractors for construction work. This isn’t limited to construction companies either. If your business spends over a certain amount on construction operations, even as a non-construction business, you can be classed as a “deemed contractor” and pulled into CIS obligations you didn’t expect.
Subcontractors are paid by contractors to carry out the actual construction work. Most self-employed tradespeople working on building sites fall into this category: electricians, plumbers, groundworkers, scaffolders, and so on.
Genuinely worth noting, you can be both at once. Plenty of businesses subcontract work out to others while also working as subcontractors for bigger contractors themselves, which means juggling obligations on both sides of the scheme.
Registering for CIS
If you’re a contractor, registration isn’t optional; you must register with HMRC before you start paying subcontractors.
If you’re a subcontractor, registration is technically optional, but here’s what most people miss: if you don’t register, you get deducted at 30% instead of the standard 20%. That’s a meaningful difference in your monthly cash flow, so realistically, almost every subcontractor should register.
Registration is done through your Government Gateway account, and you’ll need your Unique Taxpayer Reference to get set up. It’s a fairly quick process, but do it before you start work, not after your first payment’s already landed short.
The Deduction Rates Explained Properly
This is the part people genuinely want clarity on, so let’s be precise.
30% deduction applies to subcontractors who aren’t registered for CIS at all. This is the default rate if HMRC has no record of you, and honestly, it’s a painful amount to lose from every payment.
20% deduction applies to registered subcontractors who don’t hold gross payment status. This is the standard rate most subcontractors operate under.
0% deduction, known as gross payment status, means contractors pay you the full amount with nothing deducted at source, and you handle your tax entirely through your own Self Assessment return instead.
Gross payment status sounds appealing, and for a lot of established subcontractors it genuinely is, since it improves cash flow significantly. But to qualify, you need to meet turnover thresholds and pass compliance tests around your tax payment history miss deadlines or have outstanding tax debts, you won’t qualify, or you could lose it if you already hold it.
What Contractors Actually Need to Do
If you’re on the contractor side, your obligations are more involved than most people expect.
Before paying any subcontractor, you need to verify them with HMRC, which confirms their registration status and tells you what deduction rate applies. Skip this step, and you risk deducting the wrong amount, which creates problems for both sides down the line.
Each month, you’re required to submit a CIS return to HMRC, detailing every payment made to subcontractors and the deductions taken. This is due by the 19th of the month following the tax month it covers, and missing it triggers automatic penalties that build up the longer it’s left.
You also need to provide subcontractors with a payment and deduction statement each time you pay them, showing what was deducted. They need this for their own records and their Self Assessment return, so it’s not optional paperwork; it genuinely matters to the person on the other end.
What Subcontractors Need to Do
If you’re the one being deducted from, your responsibilities look different, but they’re just as important.
Keep every payment and deduction statement you receive. These are your proof of tax already paid, and without them, reconciling your Self Assessment return properly becomes a genuine headache.
File your Self Assessment tax return as normal each year, but here’s the bit that catches people out: you report your full income before deductions, then claim back the CIS deductions already taken as tax already paid. Get this backwards, and you can end up either overpaying or under-claiming what you’re actually owed.
The Repayment Situation Most Subcontractors Don’t Realise
Here’s something I explain constantly, because it genuinely surprises people. A huge number of subcontractors are owed a refund at the end of the tax year, not an additional bill.
Why? Because CIS deductions are taken as a flat 20% (or 30%) regardless of your actual expenses, allowances, or true tax position. If your legitimate business expenses bring your taxable profit down below what’s been deducted, you’re due money back.
In my experience, this is where proper bookkeeping throughout the year makes a genuinely significant financial difference. Subcontractors who track their expenses properly tools, travel, materials, protective equipment, insurance often reclaim substantial amounts they’d have simply missed with sloppy records. Are you actually tracking your allowable expenses through the year, or just hoping it works out at tax return time?
A Real Example Worth Sharing
I worked with a groundworker who’d been registered under CIS for years, having 20% deducted from every payment, and assumed that was just “his tax done.”
When we actually went through his full year-properly: fuel, tool purchases, van costs, insurance, and a chunk of home office use for admin his real tax liability came out considerably lower than the amount already deducted at source. He was due a refund of just over £3,200 that he’d never claimed in previous years because nobody had ever properly gone through his expenses against his CIS deductions.
That’s not an unusual story, honestly. It’s one of the most common situations I come across in this line of work, and it’s exactly why CIS subcontractors benefit so much from proper year-round bookkeeping rather than a rushed exercise every January.
CIS and VAT Where It Gets More Complicated
If you’re VAT registered, there’s an additional layer called the domestic reverse charge, and this trips up even experienced contractors.
Under the reverse charge, for most CIS-related supplies between VAT-registered businesses, the subcontractor doesn’t charge VAT on their invoice at all. Instead, the contractor accounts for that VAT directly to HMRC themselves. It shifts where the VAT gets declared, specifically to reduce fraud within the sector.
Get this wrong either charging VAT when you shouldn’t, or failing to account for it as a contractor when you should and it creates a genuine mess to untangle later. This is an area where I’d strongly recommend proper advice rather than guessing based on how things used to work before the reverse charge came in.
Common CIS Mistakes I See Regularly
A few patterns come up again and again, worth flagging plainly.
Subcontractors who don’t register and lose money unnecessarily to the 30% rate. Contractors who forget monthly returns, racking up entirely avoidable penalties. Subcontractors who don’t track expenses properly and miss out on legitimate refunds. And businesses that misunderstand the VAT reverse charge and either overcharge or undercharge, creating problems that take real time and cost to unpick.
My Honest Take
I think CIS gets treated by a lot of contractors and subcontractors as something to just endure: deductions happen, paperwork gets filed, and everyone moves on without really understanding the mechanics behind any of it.
But there’s real money at stake here, on both sides. Subcontractors who understand the scheme properly, keep good records, and claim what they’re actually owed end up meaningfully better off than those who just accept whatever’s deducted without question. Contractors who stay compliant avoid penalties that are entirely preventable with a bit of organisation.
Don’t just endure CIS. Understand it properly, keep your records tight, and get proper advice where the rules genuinely get complicated, because in a scheme built around percentages taken off every single payment, the details matter more than most people ever realise.