CIS Explained Simply: What Is CIS Tax?

What is CIS tax?

The first thing to understand is that CIS tax is not a tax. There is no such thing as a CIS rate on your income, no CIS band, no CIS allowance. The Construction Industry Scheme is a withholding mechanism: a way for HMRC to collect tax from an industry with a long history of cash jobs and disappearing subcontractors, by making the person paying you responsible for holding some of it back.

HMRC put it simply — under CIS, contractors deduct money from a subcontractor's payments and pass it to HMRC. Those deductions count as advance payments towards the subcontractor's tax and National Insurance. Nothing more, nothing less. The money is still yours; it is just sitting in HMRC's account instead of your bank until you file your return.

That framing matters, because it explains the two things every subcontractor eventually asks. Why is 20% taken when I only pay 20% tax and 6% NI on part of my income? Because the deduction is flat and ignores your allowances and expenses entirely. And why do I always get a chunk back? For exactly the same reason. The scheme is calibrated to over-collect and settle up later.

Contractor or subcontractor — who does CIS apply to?

Contractors

A contractor, for CIS purposes, is anyone who pays subcontractors for construction work. You do not have to be a big main contractor. If you are a solo spark who subs a day of groundwork or a bit of plastering out to another self-employed trade and pays them for it, you are a contractor for that payment and the scheme's obligations land on you: register as a contractor, verify them, deduct, file a monthly return, issue a statement.

Subcontractors

A subcontractor is anyone who does construction work for a contractor. Registration is technically optional — but not registering simply means you get deducted at the higher rate, so in practice everyone registers.

Deemed contractors

The scheme also catches businesses that are not in construction at all but spend heavily on it. If a business spends over £3 million on construction within 12 months of its first payment, it must register as a contractor even though building is not what it does. That is why a hotel group, a supermarket chain or a large landlord will run CIS on the sparks who maintain their sites.

Can you be both?

Yes, routinely, and in the same tax month. You can be a subcontractor to the main contractor above you and a contractor to the labourer below you. If that is your position, you have to register in both capacities and meet both sets of obligations.

One important exclusion: private householders are not contractors. When you rewire Mrs Doyle's bungalow and invoice her directly, there is no CIS on that job. Domestic work sits outside the scheme entirely.

What work is covered, and what is not

CIS covers construction work on permanent or temporary buildings and structures, and on civil engineering works such as roads and bridges. In practice that means:

• Site preparation — laying foundations, access works
• Demolition and dismantling
• Building work
• Alterations, repairs and extensions
• Installing systems for heating, lighting, power, water and ventilation — which is where electrical work sits
• Decorating, and cleaning the inside of a building after construction work

Work that falls outside the scheme includes:

• Architecture and surveying
• Hiring scaffolding with no labour
• Carpet fitting
• Making materials used in construction, and delivering materials
• Work on a construction site that is clearly not construction — running the canteen, site facilities

CIS for electricians

Installing systems for lighting and power is squarely inside the scheme, so the default answer for a spark working on site is: yes, CIS applies. First fix, second fix, containment, distribution boards, testing and certification as part of an install, fault-finding and remedial work on a site — all in scope when a contractor is paying you.

The dividing line is almost never about the type of electrical work. It is about who is paying the invoice. The same consumer unit change is inside CIS if a builder is paying you as part of a refurb, and outside CIS if the homeowner is paying you directly. Sparks who do a mix of site work and domestic work are effectively running two payment regimes side by side, which is exactly why your invoicing needs to keep labour and materials split on every job rather than only on the CIS ones.

Two grey areas worth flagging with your contractor before you price. Manufacturing or prefabricating materials off site is excluded from the deduction — so if you build up panels or looms in a workshop, that element is treated differently from the labour of installing them. And installing a security or alarm system on its own has its own VAT treatment under the reverse charge rules, covered further down. When in doubt, ask the contractor what they intend to report, and get it in writing before the first application for payment.

Registering and getting verified

You register for CIS with HMRC as a sole trader, a partner, or through your limited company. You will need your Unique Taxpayer Reference and, as a sole trader, your National Insurance number. If you are not yet registered for Self Assessment, do that first — the UTR is the key that everything else hangs off.

Registering is only half the job. Before the contractor pays you for the first time they must verifyyou with HMRC, giving your UTR and NI number (or company UTR and registration number) alongside their own references. HMRC tells them whether you are registered and what rate to deduct at, or whether you can be paid gross. Contractors have to re-verify a subcontractor they have not included on a CIS return in the current or the last two tax years — so if you have had a spell off a firm's books, expect to be verified again.

The practical consequence: a mismatch between the details you gave HMRC and the details the contractor submits is the single most common cause of being wrongly stuck on 30%. Give them your exact registered trading name and UTR, in writing, and check the first statement.

The three CIS rates: 20%, 30% and gross

The gap between 20% and 30% is pure cash flow. On £40,000 of labour it is £4,000 of your own money held by HMRC for up to a year for no reason other than paperwork. If you are being deducted at 30%, fixing it is the highest-value admin available to you.

What is gross payment status and how do you qualify?

Gross payment status — often just called CIS gross status — means contractors pay your invoices in full, with nothing withheld. It does not reduce your tax by a penny. What it changes is when you pay: instead of drip-feeding HMRC through the year at 20% of labour, you keep the cash, run your business with it, and pay the whole bill through Self Assessment or Corporation Tax at the year end.

For a growing firm carrying wages, materials and a van fleet, that is a serious working capital improvement. It is also a serious discipline test, which is why HMRC gates it behind three tests. You have to pass all of them.

1. The business test

You must show that your business does construction work — or provides labour for it — in the UK, and that the business is run through a bank account. Cash in hand out of a personal current account will not get you gross status.

2. The turnover test

HMRC looks at your construction turnover for the last 12 months, ignoring VAT and the cost of materials. That last part catches people out: a firm turning over £120,000 with £70,000 of materials has only £50,000 of qualifying turnover. The thresholds:

3. The compliance test

You must show that you have paid your tax and National Insurance on time in the past. This is the test most applications fail on, and it is unforgiving: late Self Assessment returns, late payments, late monthly CIS returns and late PAYE all count against you. The practical advice is to spend twelve clean months getting everything filed and paid on the day it is due before you apply, rather than applying and being refused.

Applying, and keeping it

You apply to HMRC using the form for your business structure — one for sole traders, one for partnerships, one for limited companies — online or by post. Applying for gross payment status also registers you for CIS if you have not registered already.

Gross status is not permanent. HMRC reviews it and can withdraw it if your compliance slips, at which point contractors go back to deducting 20% and your cash flow changes overnight. Treat it as something you have to keep earning, and build the filing dates into your calendar rather than your memory.

Is gross status actually worth it?

For a one-van sole trader, not necessarily. The 20% deduction is an enforced savings scheme, and plenty of sparks quietly rely on it to cover a January bill they would otherwise have spent. Take gross status and that safety net is gone: the full liability arrives at once, with payments on account on top. If you take it, put the money aside the day each invoice is paid and never touch it. For firms with staff, stock and a real working-capital cycle, the benefit is obvious and worth the paperwork.

What counts as materials

The deduction is never applied to the whole invoice. Before the percentage is worked out, the contractor takes off:

• VAT charged by the subcontractor
• Materials the subcontractor paid for
• Consumable stores — items used up doing the job
• Fuel used, except fuel for travelling
• Plant hire
• The cost of manufacturing or prefabricating materials

For a spark, “materials” is cable, containment, boards, breakers, accessories, fittings, fixings, and hired kit such as a chasing machine or a tower. Your time, your apprentice's time and your testing labour are not materials.

Two rules to respect. First, the materials figure has to be the actual cost you incurred, not an inflated number designed to shrink the labour line. HMRC scrutinises this, and a contractor who accepts an obviously inflated materials split is on the hook too. Second, if you do not itemise, you invite the contractor to deduct from the whole invoice. Every hour spent arguing about that after the payment has been made is an hour you do not get back. Split labour and materials on the quote, carry the split through to the invoice, and there is nothing to argue about.

How to calculate CIS deductions

The method is always the same three steps:

1. Start with the gross amount of the invoice.
2. Take off VAT, materials, consumable stores, fuel other than for travelling, plant hire and any manufacturing or prefabricating costs.
3. Apply 20%, 30% or 0% to what is left.

Worked through on a typical job — say £1,200 of labour and £800 of materials, and you are not VAT registered:

The £240 is not lost. It goes to HMRC against your tax and you reclaim it at the year end. At 30% the same invoice would pay out £1,640, with £360 withheld.

Monthly returns and CIS statements

CIS runs on tax months, which run from the 6th of one month to the 5th of the next. Contractors must send HMRC a monthly return by the 19th of the month following the end of the tax month — so a return covering 6 May to 5 June is due by 19 June. The return declares the payments made and confirms that the subcontractors listed are not employees; getting employment status wrong can cost up to £3,000.

If a contractor made no payments in a month, they must still file a nil return or tell HMRC the business is temporarily inactive. Silence is not an option, and the late filing penalties escalate quickly:

On the subcontractor's side, the document that matters is the payment and deduction statement. The contractor must give you one within 14 days of the end of each tax month. It is your receipt for every pound withheld, and it is what your refund claim is built on. Keep them in one place, digital or paper, and reconcile them against your own invoices monthly rather than in a panic the following January. Chase a missing statement the week it is late, not eight months later when the contractor has changed accounts package.

How you get the money back

Sole traders and partnerships

You reclaim through Self Assessment. Work out your profit — turnover less allowable expenses — then your Income Tax and Class 4 National Insurance on that profit, and enter the total CIS deducted in the CIS box on the return. HMRC nets the two off. Because the deduction ignored your personal allowance and every expense you incurred, the result is usually a repayment.

The dates: the tax year ends 5 April and you can file from 6 April. Register by 5 October if you have never filed before. The online filing deadline and the payment deadline are both 31 January. There is no advantage whatsoever in waiting — if you are owed money, filing in April rather than January gets it to you the best part of ten months sooner.

Limited companies

A company does not reclaim CIS on a Self Assessment return. It offsets the deductions suffered against its own PAYE, National Insurance, student loan and CIS liabilities through the payroll, and claims a repayment of anything left over after the end of the payroll year. If you have incorporated recently, this catches people out — the money is still recoverable, but the route is completely different.

CIS and the VAT domestic reverse charge

If you are VAT registered, there is a second rule sitting on top of CIS that trips up a lot of sparks. The VAT domestic reverse charge applies to supplies of building and construction services that are reported within CIS, between businesses that are VAT registered in the UK. Where it applies, you do not charge VAT on your invoice — the customer accounts for it instead.

It does not apply to everything. Services supplied on their own — professional work by architects or surveyors, manufacturing building components or materials, installing security systems, signage, artistic installations — fall outside it, and normal VAT rules apply. It also does not apply when the customer is an end user, such as a private householder.

The practical upshot is that a VAT-registered subcontractor working under CIS on a commercial site is often issuing invoices with no VAT on them at all, and a note telling the customer to account for the reverse charge. Get this wrong in either direction and you either hand over VAT you should not have charged, or under-declare. Our guide to the domestic reverse charge for electricians goes through it properly, and VAT for electricians covers registration and rates.

Common CIS mistakes

• Not splitting labour and materials. The single most expensive habit in the trade. A £2,000 invoice with no split invites a £400 deduction instead of £240.
• Not registering. Staying on 30% out of inertia costs you a third more cash flow than it needs to, all year, every year.
• Losing the statements. No statement, no easy proof. HMRC matches your claim against what the contractor reported, and a gap stalls the refund.
• Assuming CIS covers your whole tax bill. It usually over-collects — but not always. A year with low expenses and high labour, or income from elsewhere, can leave a balance to pay in January.
• Applying CIS to domestic work. A householder is not a contractor. There should be no deduction on a direct domestic invoice.
• Inflating the materials figure. Tempting, visible, and it puts both you and the contractor in the frame.
• Forgetting you are also a contractor. The moment you pay another self-employed trade for construction work, the monthly return obligations are yours.
• Spending the refund before it lands. It is an estimate until HMRC processes the return.