The Construction Industry Scheme applies when you operate as a contractor and pay subcontractors for qualifying construction work. It can also apply outside construction: a non-construction business becomes a deemed contractor where its construction expenditure exceeds £3 million in a rolling 12-month period. You can also be both contractor and subcontractor simultaneously — your building company may receive payments from a principal contractor while paying electricians or decorators on the same project.

Getting CIS right means having a clear process at three distinct points: before each payment is made, when the payment is recorded, and when the monthly return is filed. The CIS accounting records you keep form the thread connecting all three. Miss a step and you are either paying the wrong amount, filing incorrect figures, or scrambling to reconstruct information that should already be at hand.

Before paying a new subcontractor, you generally need to verify them with HMRC. You also need to verify a subcontractor you have used previously if they have not appeared on a CIS return in the current or previous two tax years. Verification tells you whether the subcontractor can be paid gross or whether a CIS deduction applies.

What information you need to verify a subcontractor

The details required depend on whether the subcontractor is a sole trader, partnership or limited company. You may need some combination of the following:

• Unique Taxpayer Reference (UTR)
• National Insurance number, for a sole trader
• Company name, UTR and company registration number
• Partnership UTR and nominated partner details
• Trading name, where relevant

The details must match HMRC's records exactly, so obtaining them correctly before the first payment avoids unnecessary delays.

Deduction rates after verification

HMRC tells you which treatment to apply. The rates currently in force are:

• 0% where the subcontractor holds gross payment status
• 20% for registered subcontractors subject to the standard deduction
• 30% where a subcontractor is not registered or cannot be verified

You cannot choose the rate yourself. The verification result determines how the payment must be treated. It is also worth keeping the HMRC verification information alongside your payment records, because if a query arises later you want a clear audit trail showing why a particular rate was applied — not a gap you then have to fill from memory.

Good CIS records provide a clear trail from the subcontractor's invoice through to the payment, deduction and monthly return. Under HMRC's CIS record-keeping requirements, you need to retain those records for at least three years after the end of the tax year they relate to. HMRC can ask to see them at any point, and failing to produce required records can result in a penalty of up to £3,000.

What each payment record should contain

For each relevant payment, you should be able to identify:

• The subcontractor
• The payment date
• The gross amount, excluding VAT
• Relevant materials costs
• The CIS deduction applied
• The net amount actually paid

Where materials are deducted before the CIS calculation is made, they must represent the actual cost of materials paid for directly by the subcontractor to fulfil that specific contract. A materials figure appearing separately on an invoice is not sufficient if it does not reflect the genuine direct cost.

Where to keep your CIS records

CIS works better when it forms part of your normal accounting process rather than sitting in a separate folder visited once a month. Keeping invoices, payments and deduction records within organised bookkeeping services makes reconciliation much easier before a return is submitted, rather than rebuilding the position at the deadline. The aim is simple: if HMRC asks why a figure appeared on a particular return, you should be able to follow it back to the underlying transaction without reconstructing the history from bank statements.

You must report payments made to subcontractors through a monthly CIS return. The return covers the relevant tax month — which runs from the 6th of one month to the 5th of the next — and must reach HMRC by the 19th following that period. So a return covering payments from 6 September 2026 to 5 October 2026 is due by 19 October 2026.

What the return must include

The return covers the subcontractors paid, the payments made and any deductions taken. You must also make declarations about the employment status of subcontractors and confirm that those requiring verification have been verified. These declarations carry weight: CIS does not convert an employee into a self-employed subcontractor simply because deductions are being made.

Nil returns and inactivity requests

If you make no subcontractor payments in a month, you should either submit a nil return or notify HMRC that you have temporarily stopped using subcontractors. HMRC allows an inactivity request where you expect to make no payments for up to six months.

Before you file each month

A quick pre-filing check saves a lot of corrective work. You should confirm that all subcontractor payments for the period are included, that new subcontractors have been verified, that deduction rates agree with HMRC's verification results, that materials have been treated correctly, that deduction statements can be produced, that return totals agree with your bookkeeping records, and that sufficient cash is available for the HMRC liability. That monthly rhythm is why keeping records current throughout the period is far preferable to collecting invoices just before filing.

Where you make a CIS deduction, you must give the subcontractor a payment and deduction statement within 14 days after the end of the relevant tax month. The statement records what you paid and how much CIS was deducted. It matters to the subcontractor because the deduction represents an advance payment towards their own tax and National Insurance position.

When CIS deductions are due to HMRC

CIS deductions are due within 14 days after the end of the tax month, or within 17 days where payment is made electronically — in practice, the 19th or the 22nd for electronic payments. If your average monthly payments to HMRC fall below £1,500, you may be able to pay quarterly instead, but your CIS returns still need to be submitted monthly regardless.

That distinction matters: the return deadline and the payment deadline are separate obligations. You need to distinguish clearly between what is owed and what cash remains available for wages, suppliers and other costs.

CIS when your business is both contractor and subcontractor

If you also receive payments as a subcontractor, you need to track CIS suffered separately from CIS deducted. For a limited company, CIS deductions suffered can be reported through payroll using the Employer Payment Summary and set against qualifying PAYE, National Insurance, student loan and CIS liabilities — they should not simply be treated as a Corporation Tax payment. For sole traders and partners, CIS deductions suffered are dealt with through Self Assessment.

Missing or incorrect CIS records create more than an administrative inconvenience. They lead to incorrect payments, inaccurate liabilities and penalties that a regular monthly process would have avoided.

Late-filing penalties

As of September 2026, HMRC's standard late-filing penalties are:

1. One day late: £100
2. Two months late: £200
3. Six months late: £300 or 5% of the CIS deductions shown on the return, whichever is higher
4. Twelve months late (non-deliberate failure): the greater of £300 or 5% of the liability

Where HMRC considers the withholding of information to be deliberate, or deliberate and concealed, higher penalties apply. Minimum penalties at the 12-month stage can rise to £1,500 or £3,000 depending on the circumstances.

The cash-flow risk of poor records

CIS deductions collected from subcontractor payments represent money that belongs to HMRC, not ordinary cash available for running your business. If your records are behind, it is easy to overestimate what is genuinely available. The same problem arises when CIS suffered on income received as a subcontractor has not been recorded properly. Keeping an accurate running balance of what is owed — and what is already set aside — is a basic discipline that prevents a payment deadline from becoming a cash-flow surprise.

What an incorrect deduction costs you

An incorrect deduction affects both sides of the payment. You may pay the subcontractor too much or too little, report the wrong liability to HMRC, and then need to correct both the bookkeeping and the CIS return. This is why verification, invoice details and materials records need to be checked before each payment is processed, not after.