If you run a construction business — whether you are the main contractor engaging subcontractors or a subcontractor being paid by one — the Construction Industry Scheme (CIS) is probably costing you time, cash flow headaches, and occasionally a penalty letter you did not see coming. Contractors worry about deducting the wrong amount and facing HMRC scrutiny. Subcontractors worry about having 20%, or worse 30%, of their invoice withheld with no clear idea of when they will get it back. If you have ever stared at a subcontractor invoice wondering exactly how much to actually pay, or found cash sitting with HMRC that you cannot reclaim until the end of the tax year, this article is for you. We will strip CIS back to plain English, show you exactly how the numbers work on a real invoice, and give you a checklist you can use from your very next payment run.
What the Construction Industry Scheme Actually Does
CIS is HMRC’s way of collecting tax upfront from people working in construction, in much the same way PAYE collects tax upfront from employees. If you are a contractor paying a subcontractor for construction work, in most cases you are legally required to deduct money from that payment and send it to HMRC on the subcontractor’s behalf. The subcontractor then gets credit for that deduction against their eventual tax bill — Corporation Tax if they trade through a limited company, or Income Tax and National Insurance if they are a sole trader or partnership. It helps to think of CIS as a tax instalment, not an extra cost. The money is not lost; it is tax paid early, on the subcontractor’s behalf, by the contractor. It only runs smoothly, though, if the contractor deducts the right amount, from the right part of the invoice, after properly verifying the subcontractor with HMRC first.
Verifying a Subcontractor Before You Pay Them
Before you pay a new subcontractor for construction work, you must verify them with HMRC — either through HMRC’s online CIS service or through your payroll or accounting software. This tells you which deduction rate applies. Get this step wrong, or skip it, and you risk under-deducting (which HMRC will chase you for) or over-deducting (which damages your relationship with subcontractors who rely on that cash). Verification takes a few minutes and should become a standing part of your onboarding process for every new subcontractor, not an afterthought once the invoice lands.
| Verification status | Deduction rate | When it applies |
|---|---|---|
| Gross payment status | 0% | Subcontractor has applied to HMRC and been approved to receive payments with no deduction at all |
| Verified — standard rate | 20% | Subcontractor is matched on HMRC’s CIS records but does not hold gross payment status |
| Not matched or unverified | 30% | Subcontractor cannot be matched on HMRC’s system, or you have not verified them before paying |
Gross payment status is a real cash flow advantage. Subcontractors who qualify (based on turnover, compliance history, and business structure) receive invoices paid in full, with no deduction at all, and settle their tax through the normal Self Assessment or Corporation Tax process instead. If you are a subcontractor with a strong compliance record, it is worth checking whether you qualify — it can make a meaningful difference to monthly cash flow.
Worked Example: Paying a Subcontractor’s Invoice
Let us make this concrete. ABC Build Ltd, a main contractor, receives an invoice from Dave’s Groundworks Ltd for £5,000, covering £3,500 of labour and £1,500 of materials (excluding VAT). Dave’s Groundworks Ltd has been verified with HMRC and sits on the standard 20% deduction rate — it does not hold gross payment status. A crucial, often-missed rule: CIS deductions apply only to the labour element of an invoice, never to the direct cost of materials, provided the materials cost is genuinely itemised and reasonable. If ABC Build Ltd deducted 20% from the full £5,000, it would be over-deducting and effectively taking £300 that belongs to Dave’s Groundworks Ltd.
| Labour element (CIS deduction base) | £3,500 |
| Materials element (excluded from CIS) | £1,500 |
| CIS deduction (20% × £3,500) | £700 |
| Net payment to subcontractor | £4,300 |
| Account | Dr | Cr |
|---|---|---|
| Subcontractor costs (P&L) | £5,000 | |
| Bank | £4,300 | |
| CIS tax deducted (amount owed to HMRC) | £700 |
Records the £5,000 invoice from Dave’s Groundworks Ltd, the net payment of £4,300 after 20% CIS deduction on the labour element only, and the £700 now owed to HMRC.
What Happens to the £700 You Deduct
The £700 does not simply disappear into general tax paid — it must be reported and paid over to HMRC through the monthly CIS return (form CIS300), alongside details of every subcontractor paid in that tax month, the gross amount, and the deduction made. The return is due by the 19th of the month following the end of each tax month (which runs from the 6th of one month to the 5th of the next), and payment is due by the 22nd if paying electronically (or the 19th if paying by post). Crucially, a CIS return must be filed even in a month where no subcontractors were paid — a ‘nil return’ — unless you have notified HMRC in advance of an inactivity period, otherwise HMRC’s system will issue an automatic late filing penalty. ABC Build Ltd also needs to provide Dave’s Groundworks Ltd with a written payment and deduction statement within 14 days of the end of the tax month, showing the gross payment, materials, and deduction made, because that statement is the subcontractor’s proof of tax already suffered.
The three most common CIS mistakes: deducting 20% or 30% from the materials element of an invoice rather than labour only; paying a new subcontractor before verifying their status with HMRC, which forces the 30% unverified rate or leads to under-deduction liabilities; and missing the monthly filing or payment deadlines, which triggers automatic penalties even if no tax was due. All three are entirely avoidable with a simple monthly checklist.
Reclaiming CIS Deducted From Your Own Income
Now flip to the subcontractor’s side. If the subcontractor is a sole trader (for instance, an unincorporated contractor trading under their own name), the £700 deducted is simply offset against the tax bill calculated through Self Assessment at the end of the year — it reduces the balance owed, or generates a refund if deductions exceed the final liability. If the subcontractor trades as a limited company (like Dave’s Groundworks Ltd), the process is different and often misunderstood: CIS deductions suffered by the company can be offset against its own PAYE, National Insurance, and CIS liabilities as an employer, reported through the Employer Payment Summary (EPS) each month. If the company has no employees or its PAYE liabilities are smaller than the CIS suffered, the unused balance can only be reclaimed from HMRC after the tax year ends, which means cash can sit tied up for months if it is not tracked carefully. Keeping a running schedule of CIS suffered — invoice by invoice, month by month — makes it far easier to reconcile against statements from contractors and to support a repayment claim if one becomes necessary.
Key Takeaways
- Verify every new subcontractor with HMRC before the first payment — this determines whether you deduct 0%, 20%, or 30%, and getting it wrong causes disputes and penalties.
- Only apply CIS deductions to the labour element of an invoice, never to the direct cost of materials — over-deducting damages trust and ties up a subcontractor’s cash unnecessarily.
- File the monthly CIS return (CIS300) by the 19th of each month following the tax month end and pay HMRC by the 22nd (electronically), filing a nil return when no payments occur unless HMRC is notified of inactivity.
- If you operate through a limited company and suffer CIS deductions, keep a running schedule of amounts deducted so you can offset them against PAYE/NIC each month and claim any surplus back promptly at year end.
Still unsure whether your CIS deductions are correct?
Our team helps contractors and subcontractors get CIS verification, deductions, and monthly returns right first time — so your cash flow and compliance both stay on track.
