Construction Industry Scheme (CIS): A Guide for Contractors and Subcontractors

Summer tends to be peak season for building work, with more projects running simultaneously than at any other point in the year. For anyone operating in construction, that also means the Construction Industry Scheme, commonly known as CIS, is likely to be more active in your business right now than usual. Whether you're a contractor engaging subcontractors or a subcontractor working under CIS yourself, getting the rules right matters, and the mistakes we see tend to repeat themselves year after year.

What CIS Actually Is

CIS is a scheme that requires contractors to deduct money from a subcontractor's payments and pass it directly to HMRC as an advance payment towards the subcontractor's own tax and National Insurance. It applies to most construction work in the UK, covering everything from groundworks and demolition to alterations, repairs and decorating, though certain activities such as architecture, surveying and pure scaffolding hire without labour are excluded. If your business pays subcontractors for construction work, or you're a subcontractor being paid by a contractor, CIS almost certainly applies to you in some form.

Registration and Deduction Rates

Contractors must register for CIS before taking on any subcontractors. Subcontractors can also register, and doing so directly affects how much is deducted from their payments. Registered subcontractors have tax deducted at the standard rate, while those who haven't registered face a significantly higher deduction rate on everything they're paid. Subcontractors with a strong compliance history and a good track record can apply for gross payment status, meaning no deduction is made at all and they handle their own tax through Self-Assessment or Corporation Tax instead - this is worth working towards if your business qualifies, since it significantly improves cash flow.

Verifying Subcontractors Properly

Before paying a new subcontractor for the first time, contractors are required to verify their CIS status with HMRC, which confirms the correct deduction rate to apply. This step is easy to overlook when work needs to start quickly, but skipping it is a common source of compliance problems - deducting the wrong rate, or none at all, because verification wasn't completed properly before the first payment was made.

Materials Versus Labour

One of the most common errors we see is contractors deducting CIS tax from the full invoice value, including the cost of materials, rather than just the labour element. CIS deductions should only apply to the labour part of a subcontractor's invoice - genuine material costs, provided they're clearly itemised and reasonable, are excluded from the deduction. This means invoices need to separate labour and materials clearly; a vague, lump-sum invoice makes it far harder to apply the deduction correctly and can lead to over-deduction, effectively giving the subcontractor an interest-free loan to HMRC that only gets resolved when their tax return is filed.

Monthly Returns and Deadlines

Contractors need to submit a monthly CIS return to HMRC, even in months where no payments were made to subcontractors, reporting the deductions taken and confirming subcontractor details. These returns are due by the 19th of each month following the tax month they relate to, and penalties apply for late submission, starting at £100 and increasing the longer a return remains outstanding. Given how easy it is to lose track of a monthly deadline alongside everything else running through a busy summer construction schedule, this is an area where a missed deadline often isn't noticed until a penalty notice arrives.

For Subcontractors: Reclaiming What You're Owed

If you're a subcontractor having CIS deducted from your payments, it's worth remembering that those deductions are advance payments towards your own tax bill, not a final tax charge. When you file your Self-Assessment return, your actual tax liability is calculated properly, taking into account your real expenses and allowances, and any excess CIS deducted during the year is refunded. Many subcontractors are due a refund every year simply because CIS deductions, taken at a flat rate on gross labour income, tend to overshoot their actual tax liability once genuine business expenses are accounted for - filing promptly after the tax year end means that refund arrives sooner rather than sitting with HMRC unclaimed.

Keeping CIS Simple

The businesses that manage CIS with the least friction tend to be the ones with clear processes: subcontractors verified before the first payment, invoices that separate labour and materials properly from the outset, and monthly returns submitted on a fixed date rather than remembered at the last minute. If your current process feels more chaotic than that, particularly during a busy season like this one, it's worth getting it properly set up now rather than carrying the same stress into next summer.