Failing to separate materials from labour on your invoices is a common and expensive mistake. Under CIS rules, tax should only be deducted from the labour portion of your work. Proper itemisation can save you hundreds of pounds in immediate cash flow every month.

CIS Invoicing: The Single Line That's Costing You £160+ Every Week

CIS Tax · Cash Flow · UK Construction

The Invoice Line You're Missing Is Costing You £160 Every Single Week

Under CIS, your contractor doesn't deduct tax on materials — only on labour. Yet most subcontractors write one lump-sum figure and hand HMRC a tax deduction they were never owed.

You've finished a job. Materials cost you £800 out of pocket. Labour was £1,200. You send an invoice for £2,000, your contractor deducts 20% CIS, and you receive £1,600.

The problem? That 20% should only apply to your labour. HMRC's own rules are clear: CIS deductions do not apply to the cost of materials. By sending a lump-sum invoice, you've just paid £160 in unnecessary tax — money that was yours, sitting in HMRC's account until you reclaim it at the end of the tax year.

Multiply that by 48 working weeks and you've given the government a £7,680 interest-free loan. Not because you owed it. Simply because your invoice had one line instead of two.

The Cost of a Lump-Sum Invoice

£2,000 invoice · £1,200 labour / £800 materials · 20% CIS rate

Lump-sum invoice

£400 deducted

Tax applied to full £2,000

Itemised invoice

£240 deducted

Tax applied to labour only

Immediate gain per invoice: +£160 cash in hand · Up to £7,680/year on weekly work

Why Contractors Won't Fix This for You

When your invoice doesn't separate labour from materials, the contractor faces a choice: calculate the correct split themselves — or deduct from the full amount to be safe. In almost every case, they'll choose the safer option. Their liability to HMRC is reduced, their admin is simpler, and the cost falls entirely on you.

This isn't malicious. It's structural. The CIS scheme places the burden of proof squarely on the subcontractor. If you can't demonstrate what the materials cost was, the contractor has no obligation to assume one exists.

A vague invoice isn't just a paperwork issue — it's capital frozen in the tax system, unavailable to you until year-end, earning nothing, whilst your supplier bills sit unpaid.

What HMRC Considers "Materials"

Not everything qualifies. The following costs are excluded from CIS deductions when correctly itemised:

Building materials: Bricks, timber, steel, cabling, pipework — anything permanently incorporated into the works.
Consumables: Drill bits, sandpaper, screws, fixings, and similar items used in carrying out the work.
Bare plant hire: Equipment hired without an operator — excavators, access towers, compressors. If the operator is included, it becomes labour.
Fuel for hired plant: Fuel you purchase specifically for equipment you are hiring.

VAT Reverse Charge: If you are VAT-registered and working for a VAT-registered contractor, the Domestic Reverse Charge applies. CIS is calculated on the net labour figure — before VAT. Getting this wrong can trigger an HMRC compliance check and result in significant penalties or overpayments.

A Real Scenario: The Week You Stop Leaving Money Behind

Example · First Fix Electrician · 20% CIS Rate

Marek has just completed a week's first-fix on a new build. He supplies his own cable, back-boxes and containment. His invoice this week:

Labour: £900
Materials (cable, trunking, fixings): £620
Total invoice: £1,520

Old way (lump sum): CIS deducted on £1,520 → he receives £1,216.

Correct way (itemised): CIS deducted on £900 only → he receives £1,340. £124 more in his account that Friday.

Checklist: A Compliant, High-Yield Invoice

Step	Action Required	Why It Matters
01	Separate Labour from Materials Use two distinct line items on every invoice, not a single total figure.	Without this split, the contractor can legally deduct CIS from everything.
02	Keep Your Receipts Retain purchase receipts or supplier invoices for every material cost you itemise.	HMRC can challenge the split. Without proof, the deduction stands.
03	Apply VAT Reverse Charge Correctly CIS is calculated on net labour. Do not apply it to the VAT amount.	Miscalculation here is one of the most common triggers for a compliance check.
04	Verify Your UTR Is Registered Confirm your details match HMRC records before the first payment is made.	An unmatched or unverified UTR results in a 30% deduction rate instead of 20%.

How Much Are You Actually Owed?

If you've been submitting lump-sum invoices with significant material costs — and most subcontractors in groundworks, electrical, plumbing, and fit-out trades carry substantial material values — you have almost certainly overpaid CIS tax. That overpayment sits in your HMRC account and can be reclaimed through your Self Assessment return.

This is not a grey area, and it's not aggressive tax planning. It is the correct application of HMRC's own rules. The deduction was never supposed to apply to materials. You are simply taking back what was always yours.

Action today: Open your most recent invoice. If there is one total figure and no separate materials line — that invoice cost you money. Update your template before your next job. If you need to review historic overpayments, speak to a CIS-specialist accountant about what's recoverable through Self Assessment.