Construction Industry Scheme (CIS) Explained: Deductions, Verification, Monthly Returns and Refunds

What is the Construction Industry Scheme?

The Construction Industry Scheme (CIS) is a UK tax mechanism for specified payments by construction contractors to subcontractors. A contractor normally deducts an HMRC-specified percentage from the part of a payment subject to CIS and pays it to HMRC. The deduction is an advance payment towards the subcontractor’s tax obligations, not a separate tax charged on top of the invoice.

The scheme affects far more than large building firms. It can cover main contractors, subcontracting trades and some businesses whose principal trade is not construction. Its rules depend on the work actually performed, who makes the payment and the tax status of the subcontractor.

This guide is written for UK contractors and subcontractors who want to verify people correctly, calculate deductions accurately, manage the 19th-of-the-month return deadline and recover deductions where appropriate. It does not replace a contract-specific employment status or VAT review.

Who must register as a CIS contractor or subcontractor?

A business paying subcontractors for construction work normally needs to register as a CIS contractor before engaging them. HMRC also has a deemed contractor rule: a business outside construction can enter CIS where qualifying construction expenditure exceeds £3 million under the relevant rolling 12-month test.

Subcontractors can be sole traders, partnerships or limited companies providing covered construction operations to contractors. Subcontractor registration is not the same as contractor registration: failure to register as a subcontractor generally leads to higher deductions rather than making the relationship disappear from CIS. Some businesses occupy both roles, receiving payments under deduction while making their own payments to subcontractors.

Private householders paying for work on their own homes generally are not treated as CIS contractors solely because of that work. However, developers and businesses building or repairing premises for business purposes should consider the detailed coverage rules.

Which types of construction work are covered — and what is excluded?

Typical covered operations include building, altering, repairing, extending and demolishing structures, site preparation, civil engineering work and certain installation work. Examples often include groundworks, bricklaying, plastering, roofing, electrical work and plumbing undertaken as part of relevant construction operations.

Work that is purely architectural, surveying or consultancy can be outside CIS when considered on its own; however, mixed contracts may still fall within the scheme. The label “consultancy” or “maintenance” on an invoice does not settle the issue. Identify the actual services, the scope of the contract and who is supplying them.

The authoritative starting point is HMRC’s overview of CIS and its detailed CIS340 guidance.

CIS deductions: 20%, 30% or gross payment

A contractor must use the subcontractor status confirmed by HMRC, rather than choosing a rate based on preference or invoice wording. The common statuses are:

A “gross payment” subcontractor is still within the scheme and relevant payments are generally included on the contractor’s monthly return. The percentage does not apply indiscriminately to the whole invoice; VAT and the qualifying cost of certain materials and items must be considered.

How to verify a subcontractor before making payments

Contractors normally verify a new subcontractor with HMRC before paying them. Verification confirms whether the subcontractor is registered and which deduction status applies. Reverification may also be required for a previously used subcontractor who has not been included on a return in the current or previous two tax years.

Typical details include the subcontractor’s legal/trading name, UTR and, depending on business type, National Insurance number or company registration number. Inaccurate names or UTRs can lead to unsuccessful verification and a 30% deduction rate. Maintain a verification reference and the date/status returned by HMRC.

1. Check that the proposed worker is genuinely self-employed for the engagement; CIS does not override employment-status rules.
2. Gather identifying information and relevant company or partnership details.
3. Verify through HMRC or compliant commercial software.
4. Record the confirmed deduction status and reference.
5. Review subsequent HMRC status changes and only then calculate payment.

See HMRC: verify subcontractors.

Worked example: labour, materials and a 20% deduction

Assume a registered subcontractor invoices for £12,000 before VAT, consisting of £9,000 of labour and £3,000 of directly purchased qualifying materials. The contractor has verified the subcontractor at 20%. The relevant CIS deduction base is £12,000 − £3,000 = £9,000, producing a deduction of £1,800. Ignoring VAT for this illustration, the cash payment to the subcontractor is £10,200 and £1,800 is paid to HMRC.

If HMRC instead confirms 30% status, the deduction on the same £9,000 base would be £2,700. If the subcontractor has gross-payment status the CIS deduction is £0. VAT treatment needs to be checked separately: whether VAT appears on the invoice and who accounts for it can depend on the domestic reverse-charge rules.

Materials, plant hire, VAT and common calculation mistakes

HMRC says the CIS deduction is computed after excluding VAT and certain permitted direct costs, including qualifying materials paid for by the subcontractor and relevant plant-hire/consumable costs. Contractor-supplied materials or arbitrary “material allowances” should not be subtracted simply because the invoice includes a materials line.

Ask for evidence such as supplier invoices and receipts. The materials amount must reflect actual direct costs qualifying under the rules. Subcontractor travel and subsistence are not generally excluded from the CIS deduction base in the same way. A spreadsheet that deducts CIS from the invoice grand total, including VAT, is a frequent source of errors.

CIS and VAT are separate systems. Under the construction domestic reverse charge, a qualifying supplier does not charge VAT in the normal way and the customer accounts for it, provided the detailed conditions are satisfied. This is not automatic for every construction transaction: check VAT registration, CIS reporting, tax status of the supply and end-user or intermediary-supplier notification. See HMRC’s construction VAT reverse-charge guidance.

Monthly CIS returns: the tax month and the 19th deadline

A CIS tax month generally runs from the 6th of one calendar month to the 5th of the next. Contractors must submit their monthly return to HMRC by the 19th following the end of that tax month, listing relevant gross payments, materials and deductions, including payments to those with gross-payment status.

The return includes declarations about employment status and verification. From 6 April 2026, HMRC’s guidance reinstates the requirement for mainstream contractors with no subcontractor payments to make a nil return or notify HMRC of a period of inactivity; check the circumstances rather than assuming “no payments means no filing”.

Under current published guidance, payment of CIS deductions to HMRC is generally due by the 22nd when paying electronically or the 19th if paying by post. These payment deadlines and the monthly return deadline are not the same obligation.

If deductions have been made, payment-and-deduction statements must normally reach subcontractors within 14 days after the tax month ends. Source: HMRC CIS monthly returns and HMRC paying deductions.

CIS late filing penalties: how they really accumulate

Missing the return deadline can trigger an initial £100 fixed penalty. If the return remains outstanding two months later, a further £200 may apply. At six months, the additional penalty is generally the higher of £300 or 5% of CIS liability; at 12 months a further penalty is due with greater amounts possible for deliberate withholding.

This is more precise than claiming every late month costs a fixed £300. The actual penalty amount, appeal rights, any reasonable excuse and whether a first-return cap applies depend on HMRC’s rules. Review the authoritative CIS late-return penalty factsheet.

A timely nil return or valid inactivity notification is preferable to leaving the filing status unresolved. Penalties for failing to maintain payment statements or materially incorrect returns can also arise independently.

How subcontractors claim CIS deductions back

CIS is an advance tax payment, so the method of getting credit depends on whether the subcontractor is an individual or operates through a company. Sole traders and partners normally report gross income and CIS deductions on Self Assessment, where the deductions are credited against the relevant tax liability and any excess may be repaid.

A limited-company subcontractor follows the separate HMRC procedure for offsetting CIS deductions suffered against PAYE and other permitted liabilities, generally via the Employer Payment Summary where appropriate, and claiming any eligible balance through the approved process. Do not attempt to deduct suffered CIS payments directly from Corporation Tax on the CT600 as if it were a Corporation Tax payment.

Keep monthly deduction statements, invoices, payroll records and supporting reconciliations. Without that audit trail, refunds can be delayed or questioned. Official guidance: HMRC paying tax and reclaiming CIS deductions.

CIS and IR35: two separate questions

Being registered under CIS does not conclusively establish that a worker is self-employed. Contractors must assess employment status on the actual working arrangements. A person employed for tax purposes should not simply be pushed through CIS to avoid PAYE or employment-law responsibilities.

Where workers supply their services through a personal service company, the off-payroll working regime may also require a separate IR35 analysis. The fact that a construction business has correctly verified a subcontractor for CIS does not decide every tax-status issue.

Britvex’s construction workflow should therefore connect subcontractor verification, contracts and actual working practice to payroll decisions and record keeping—not only to the monthly return.

Construction bookkeeping: beyond the CIS return

A compliant CIS return does not mean the project is profitable. Construction businesses need costs attached to jobs: direct labour, subcontractor payments, materials, plant, vehicles, subcontractor retentions, staged applications, VAT and overhead. If these remain in separate spreadsheets, annual accounts may be accurate but management may have no reliable view of margin by project.

For example, receiving £30,000 of cash at a milestone does not mean £30,000 is free to spend. Part of the balance may relate to unpaid materials, retentions, PAYE/CIS, VAT liabilities or committed subcontractor costs. A job-level ledger and cash-flow forecast help directors distinguish project cash from available company funds.

Britvex can connect construction accounting, contractor and CIS services, bookkeeping and VAT support where applicable.

A practical CIS contractor checklist

Use this routine before making the first payment and before the monthly deadline:

1. Decide whether the work and the payer fall inside CIS, including any deemed-contractor test.
2. Check genuine employment/self-employment status on actual working practices.
3. Register and verify each subcontractor using accurate identification details.
4. Obtain reliable evidence for qualifying direct materials and plant costs.
5. Calculate deductions from the correct base and record gross payments, materials and tax withheld.
6. Issue deduction statements on time and pay HMRC through the PAYE/CIS account.
7. File the monthly return by the 19th or make a valid nil/inactivity declaration as required.
8. Reconcile CIS to VAT, project costs, payroll, bank payments and the general ledger.

Businesses with incomplete records or historic missed returns should address the position promptly rather than wait for another penalty. A focused Britvex consultation can determine whether the immediate requirement is a filing correction, a refund reconciliation, a reverse-charge review or a full construction accounting workflow.