The £200 You're Handing HMRC Every Friday — Without Knowing It
In the UK construction industry, cash flow isn't just about how much you earn — it's about how much actually lands in your account on Friday. One invoicing habit is quietly draining that figure every single week.
Think about the last invoice you sent. Did it show one total — labour and materials combined as a single figure? If so, your contractor had no choice but to deduct CIS from the full amount. Including the money you'd already spent on materials before you even started the job.
HMRC's rule is clear: CIS deductions apply to labour only. Materials, consumables, and bare plant hire are exempt. But that exemption only exists if your invoice shows them separately. Without that line, the contractor deducts from everything — and you wait until year-end to claw it back through Self Assessment, if you even know to claim it.
The Hidden Friday Shortfall
£2,000 invoice · £1,000 labour / £1,000 materials · 20% CIS rate
It's Not a Tax Problem. It's a Template Problem.
Most subcontractors who are overpaying CIS aren't doing anything wrong on site. They're not misclassifying their work or understating their income. They're just sending the invoice their mate sent them three years ago — one total, no breakdown.
The contractor isn't cheating you either. When there's no material split on the invoice, deducting from the full amount is the legally safe move for them. Their liability to HMRC is minimised. Yours is not.
What Counts as Exempt Materials?
Not everything you buy qualifies. These cost categories are excluded from CIS deductions when correctly itemised on your invoice:
- Building materials: Timber, bricks, cement, cable, pipework — anything permanently incorporated into the finished works.
- Consumables: Screws, nails, drill bits, sealant, tape, and similar items consumed in carrying out the job.
- Bare plant hire: Machinery or equipment hired without an operator — excavators, access platforms, compressors. If the operator is included, it's labour.
- Fuel for hired plant: Fuel you purchase directly for equipment you are hiring, not your own van or tools.
A Real Week: What the Difference Looks Like
Tomasz is laying drainage on a new housing site. He supplies his own aggregate, pipe, and ducting. This week's invoice breaks down as:
- Labour: £1,000
- Materials (aggregate, pipe, ducting, fixings): £1,000
- Total invoice: £2,000
Old way (lump sum): CIS on £2,000 → £400 deducted → Tomasz receives £1,600 on Friday.
Correct way (itemised): CIS on £1,000 labour only → £200 deducted → Tomasz receives £1,800 on Friday. Same job. Same hours. £200 more.
Three Changes That Cost Nothing to Make
| Step | What to Do | Why It Matters |
|---|---|---|
| 01 | Split every invoice Two line items minimum: "Labour" and "Materials & Plant." Never a single total. |
Without the split, contractors are legally entitled to deduct from the full amount. |
| 02 | Keep your receipts Retain purchase receipts or supplier invoices for every material cost you declare. |
HMRC can challenge the split. Without proof, the deduction stands regardless. |
| 03 | Confirm your UTR is verified Make sure your details match HMRC records before your first payment with any contractor. |
An unverified or mismatched UTR triggers a 30% deduction rate instead of 20%. |
The Fastest Pay Rise You Can Give Yourself
You don't need to win a bigger contract, negotiate higher day rates, or work additional hours to increase what you take home on Friday. You need to update a template. If your current invoice has one figure where there should be two, that single change is worth hundreds of pounds a month — and potentially thousands when you account for what you've already overpaid and can reclaim.
Pull up your last three invoices now. If any of them show a single total with no material breakdown, you know what to do.
Do this today: Open your invoice template and add two separate lines — Labour and Materials. Save it. Use it on your next job.
If you've been on lump-sum invoices for more than six months, speak to a CIS-specialist accountant about recovering historic overpayments through your Self Assessment return. The window to reclaim doesn't stay open indefinitely.
Frequently Asked Questions
Common questions from CIS subcontractors
How do I correctly split labour and materials on a CIS invoice?
List them as two separate line items — never combine them into a single total. Label one line "Labour" and the other "Materials & Plant Hire." Your CIS deduction is then calculated by your contractor on the labour figure only. Keep purchase receipts for every material cost you declare, as contractors and HMRC can request proof.
Which specific items are exempt from CIS deductions?
HMRC excludes the following from CIS tax when correctly itemised: building materials (bricks, timber, steel, cable, pipework) permanently incorporated into the works; consumables such as screws, nails, drill bits, and sealant; bare plant hire — machinery or equipment hired without an operator; and fuel purchased specifically for hired plant. Your own tools, van costs, and any hired plant that includes an operator do not qualify and are treated as labour.
How do I reclaim overpaid CIS tax from previous years?
Overpaid CIS is reclaimed through your Self Assessment tax return. You declare the gross income you received, HMRC calculates your actual tax liability, and any CIS already deducted in excess of that liability is refunded — usually within a few weeks of filing. You can reclaim overpayments going back up to four tax years. If you have been submitting lump-sum invoices for some time, a CIS-specialist accountant can help you calculate what is recoverable and ensure the claim is filed correctly.
Why is my CIS deduction rate 30% instead of 20%?
A 30% deduction rate means your contractor was unable to verify your details with HMRC — usually because your UTR (Unique Taxpayer Reference) doesn't match HMRC records, your business name is registered differently, or your UTR hasn't been registered under CIS at all. To fix this, contact HMRC's CIS helpline (0300 200 3210) to confirm your registration and ensure all details match exactly. Once verified, your contractor can update your rate to 20% (or 0% if you qualify for gross payment status).
Can I reclaim CIS overpayments from tax years that are now closed?
Yes — but only within HMRC's four-year window. For example, in the 2025/26 tax year you can still amend returns going back to 2021/22. Once a tax year falls outside that window, the overpayment cannot be reclaimed. If you have been using lump-sum invoices for several years and suspect significant overpayments, act promptly. A CIS-specialist accountant can assess each year, file amended returns where needed, and chase HMRC for any outstanding refunds.