What Is CIS Tax and Who Does It Apply To?

There is a tax scheme running underneath every construction site in the UK, and most of the people it applies to either don't fully understand it or are quietly getting parts of it wrong every month.

That scheme is CIS. The Construction Industry Scheme. And HMRC did not design it to be convenient.

CIS is a HMRC payroll deduction scheme that applies to contractors and subcontractors in the UK construction sector. When a contractor pays a subcontractor for construction work, they are legally required to deduct a percentage of that payment before handing it over — and pass that deduction to HMRC as an advance against the subcontractor's tax and National Insurance bill.

It exists because construction has historically been a sector where cash moved fast, records moved slow, and tax had a habit of disappearing entirely. HMRC introduced CIS to put the liability upstream — onto the contractor — so the money gets collected before it ever reaches the sub's pocket.

Simple in principle. Genuinely complicated in practice.

Who Does CIS Apply To?

CIS applies to any business or sole trader operating in the UK construction sector — either as a contractor paying others, or as a subcontractor receiving payment.

The contractor is the one with the legal obligation. They verify. They deduct. They file. They pay HMRC. The subcontractor has a different obligation: register, invoice correctly, and reconcile the deductions against their tax bill at year end.

If you pay anyone to do construction work on your behalf, you are a contractor under CIS. It does not matter how you pay them — cash, bank transfer, BACS. The obligation is triggered by the nature of the work and the relationship, not the payment method.

Businesses that must register as contractors include builders, groundworkers, landscaping companies doing construction-related work, property developers, and any company that spends more than £3 million annually on construction operations — including some local authorities and housing associations.

What Counts as "Construction Work"?

HMRC's definition is deliberately wide.

Covered: site preparation, excavation, foundations, building and structural work, alteration, extension, repair, demolition, installation of heating systems, electrical systems, air conditioning, water and drainage, roofing, plastering, painting and decorating where part of a construction contract.

Not covered: architecture, surveying, scaffold hire without labour, carpet fitting as a standalone job, furniture installation, work on residential properties done directly by the homeowner.

The grey areas are real. Landscape gardening is sometimes in, sometimes out, depending on whether it's classified as civil engineering. Security systems depend on installation context. When in doubt, the default assumption should be that CIS applies — the penalty for not deducting when you should is worse than the inconvenience of deducting when you didn't need to.

The Three Deduction Rates

This is where the money is. Or isn't.

20% — the standard rate for subcontractors who are registered with HMRC and have been verified. Most subs sit here.

30% — the rate for subcontractors who cannot be verified. Either they haven't registered, their details don't match HMRC's records, or you haven't gone through the verification process before paying them. This is where the costly errors live.

0% — gross payment status. The sub has applied to HMRC, met the compliance and turnover thresholds, and been approved to receive full payment without deduction. A contractor must still verify that the sub holds gross payment status — it doesn't just happen automatically because the sub says so.

The 30% rate is the one that causes real pain. Not because it's HMRC taking too much — they'll reconcile it through the sub's tax return — but because no subcontractor wants to receive 70p in the pound when they expected 80p. The call that follows is not a pleasant one. And if you've been paying someone without verifying them for months, you've been making that error every single time.

The Monthly Return — What It Is and When It's Due

Every contractor must submit a CIS monthly return to HMRC by the 19th of each month, covering the previous tax month. The return lists every subcontractor paid in that period, the gross payment, any materials deduction, and the CIS amount withheld.

No exceptions. No quarters. Every month. Even if you paid no subcontractors that month — you still file a nil return, or you take the penalty.

The penalty for missing the return starts at £100. After two months it's £200. After six months it's £300. After twelve months HMRC determines a penalty based on the amount of CIS deductions that should have been made — which can be significantly higher.

HMRC also charges interest on late payments of CIS deductions. The current rate sits above base rate and compounds.

Gross Payment Status — the Subcontractor's Goal

Gross payment status is the thing every established subcontractor wants and not all of them get.

To qualify, the subcontractor must demonstrate to HMRC that their tax and National Insurance obligations are up to date, that they run a genuine business, and that their net construction turnover exceeds the relevant threshold — currently £30,000 for sole traders and higher for companies and partnerships.

HMRC reviews gross payment status annually. It can be revoked if the subcontractor's compliance record slips. When it's revoked, they go back to 20% deductions and have to reapply to get it reinstated.

For a high-turnover subcontractor, the cash flow difference between 0% and 20% deductions is substantial. It is a commercially significant status. Contractors should verify it before every payment, not just once — because it can be removed without notice.

The Verification Process — Not Optional

Before you pay a new subcontractor for the first time, you must verify them with HMRC.

Verification tells you three things: whether the subcontractor is registered for CIS, what deduction rate applies, and whether they hold gross payment status. You cannot determine the correct rate any other way. Accepting the subcontractor's word is not verification. Having their UTR number is not verification. Seeing their CIS registration certificate is not verification.

You verify through HMRC's CIS online service, or through your payroll software, or through a bureau like bookd. that handles it as part of the monthly compliance cycle. You keep a record of the verification reference. You keep it in case HMRC ever asks.

If you skip verification, you default to 30%. Every time. With no route to retrospective correction unless you can demonstrate the sub was entitled to a lower rate — which requires the verification you didn't do.

What Actually Goes Wrong

Most CIS errors fall into three categories.

Not verifying before the first payment. The sub is known. There's trust. The work starts on Monday and the admin gets done later. Later becomes never. The deductions go out at the wrong rate and reconciling it six months down the line is a headache nobody needed.

Materials versus labour split. CIS deductions apply to labour. They don't apply to the materials element of an invoice — but only materials that are directly incorporated into the work. If a subcontractor includes materials in their invoice and a contractor deducts CIS on the whole amount, they've over-deducted. If the sub inflates the materials figure to reduce the deduction, that's a different problem. Getting the split documented and consistent is not optional.

Missing the monthly return. The return goes in late, or doesn't go in at all, because whoever was responsible assumed someone else was handling it. HMRC doesn't assume. They send a penalty notice.

bookd. manages CIS verification, deduction calculation, deduction statements, and monthly returns as a fixed-fee managed service for contractors across the UK.

If you're running CIS yourself and you're not completely certain the verification is happening before every first payment, the rates are right, and the monthly return is filed by the 19th — the gap between what you think is happening and what HMRC will find in a compliance check is worth closing before they come looking.