The Construction Industry Scheme (CIS) sets the tax rules that bind contractors: the businesses that engage and pay subcontractors for construction work in the UK. A CIS contractor registers with HMRC, verifies every subcontractor before the first payment, deducts 20%, 30% or 0% from each payment, files a monthly return by the 19th, and passes the deductions to HMRC alongside its PAYE tax and National Insurance.
This guide covers the contractor’s side of the scheme end to end: who must register, including the £3 million deemed contractor rule; how verification and payment work; the return and payment deadlines; the penalty ladder for late filing; and the records HMRC expects. Subcontractors receiving deductions face a separate set of duties on their own side of the scheme; a contractor who understands both sides runs a cleaner payroll and fewer HMRC queries.
Who Must Register as a CIS Contractor?
A business must register as a CIS contractor when it pays subcontractors for construction operations, or when its construction spend passes £3 million under the deemed contractor rules. HMRC applies 2 registration triggers, and either one creates the full set of contractor duties.
The first trigger covers any business that pays subcontractors to do construction work. The business structure is irrelevant: sole trader, partnership and limited company all register identically. Registration runs through HMRC’s CIS online service and requires the business’s Unique Taxpayer Reference (UTR). Registration belongs before the first subcontractor is engaged, not after the first payment is made.
The second duty sits before both triggers. Check employment status before engaging anyone. Treating a worker as a subcontractor when the engagement meets HMRC’s employment tests risks penalties and back-dated PAYE liabilities. The check takes minutes; the record of it belongs in the contractor’s CIS file.
What is the deemed contractor £3 million rule?
The deemed contractor rules make a non-construction business a CIS contractor once it spends more than £3 million on construction in the 12 months since its first payment. The rule catches businesses whose core trade is not construction but whose construction spend is substantial: property-owning businesses and infrastructure-spending businesses are the 2 categories HMRC most often pulls into the scheme this way.
Any business form counts under the rule: sole trader, partnership, limited company. Below £3 million of construction spend, and outside construction work itself, CIS contractor duties do not attach. The £3 million threshold is measured on a rolling basis from the first payment, so a growing business re-tests its spend as each month closes.
Registration deadlines, employment-status calls and the £3 million test are standing items for our contractor accountants in Newcastle, who handle CIS registrations for North East businesses across every sector the deemed rules reach.
How Do You Verify and Pay Subcontractors?
Subcontractors are verified with HMRC before their first payment, then paid net of a CIS deduction at the rate HMRC confirms: 20%, 30% or 0%. Verification is a data check, not an approval process; HMRC confirms whether the subcontractor is registered and which deduction rate applies to the engagement.
Verification runs through the HMRC CIS online service. The result, including the rate and the date, is recorded and kept. One repetition rule applies: re-verify any subcontractor who has not appeared on one of your CIS returns in the current or last 2 tax years. HMRC treats a lapsed engagement as unverified until the check is run again.
Which CIS deduction rate does HMRC confirm?
HMRC confirms one of 3 rates at verification: 20% for a registered subcontractor, 30% for an unregistered subcontractor, and 0% for a subcontractor holding gross payment status. The table below defines each rate and what it means for the subcontractor receiving the payment.
| Rate | Applies to | Effect for the subcontractor |
|---|---|---|
| 20% | Registered subcontractors, verified with HMRC | Deduction counts toward the subcontractor’s tax and National Insurance bill |
| 30% | Unregistered subcontractors | Higher deduction, repayable through the subcontractor’s own tax affairs |
| 0% | Subcontractors with gross payment status | Paid gross; tax settles through the subcontractor’s normal returns |
For the contractor, the rate changes the deduction figure only; the payment mechanics stay identical at every rate. The deduction is an advance payment toward the subcontractor’s tax and National Insurance, not an extra tax on the contractor. The contractor deducts, reports, and hands the money to HMRC; the subcontractor’s own position settles the final bill.
How do materials change the deduction?
The deduction applies to the payment excluding the cost of materials the subcontractor paid for directly. Materials are deducted from the figure first, the CIS rate then applies to the labour remainder, and material receipts are kept available on request.
A worked example: a subcontractor invoices £2,000, of which £600 covers materials purchased directly. The 30% rate applies to £1,400, producing a £420 deduction. The contractor pays £1,580 in total: £980 net labour plus the £600 materials. At the 20% rate the same invoice produces a £280 deduction and a £1,720 payment.
Each month, every subcontractor paid receives a payment and deduction statement showing the gross amount, the cost of materials, the deduction, and the net paid. Because CIS deductions run alongside PAYE, many contractors fold the statements and the deduction calculations into outsourced payroll services.
When Are CIS Returns and Payments Due?
CIS monthly returns are due by the 19th of the month following each tax month, and the deductions reach HMRC with PAYE tax and National Insurance by the 22nd electronically or the 19th by post. Two clocks run in parallel: the return deadline and the payment deadline.
Tax months run from the 6th of one month to the 5th of the next. A return covering 6 May to 5 June is due by 19 June. The return lists every subcontractor paid in the tax month and the deductions made, and is filed through the HMRC CIS online service. A month with no subcontractor payments still requires a nil return; the obligation to file never pauses.
How are CIS deductions paid to HMRC?
CIS deductions join PAYE tax and National Insurance in one payment per month or quarter. Electronic payments clear by the 22nd; postal payments reach HMRC by the 19th. Late payment attracts interest and penalties on top of the CIS figures themselves, and the interest clock starts the day after the deadline.
What penalties apply to a late CIS return?
A late CIS return attracts £100 at 1 day late and climbs a fixed ladder to £3,000 or 100% of the deductions. The table below lists each step of HMRC’s penalty ladder and the amount charged.
| Return filed | Penalty |
|---|---|
| 1 day late | £100 |
| 2 months late | £200 |
| 6 months late | £300 or 5% of the deductions on the return, whichever is higher |
| 12 months late | A further £300 or 5%, whichever is higher |
| Beyond 12 months | Up to £3,000 or 100% of the deductions |
The ladder stacks: a return 12 months late carries the earlier charges plus the later ones. Appeals go through HMRC’s online service within 30 days of the penalty notice, and the appeal states the grounds directly against the charge.
What Records Must a CIS Contractor Keep?
A CIS contractor keeps complete records for each subcontractor covering verification, payments, materials and deductions. HMRC reviews these records against the monthly returns, so each item connects to a figure already filed.
The record set for each subcontractor contains 6 elements:
- Verification results returned by HMRC, with the rate and the date
- Gross amounts paid in each tax month
- Cost of materials included in each payment, supported by receipts
- Deductions made, at the rate verified
- Copies of the monthly payment and deduction statements issued
- Proof of the employment-status checks made before engagement
Changes to the business are reported to HMRC as they happen: address changes, changes to the business structure, and changes of ownership all go through the CIS service. Corrections to a filed return are made through the HMRC CIS online service rather than by filing a second return for the month.
Records that survive an HMRC review without gaps are the point of structured bookkeeping services: the verification trail, the statements, the material receipts and the status checks sit together, month by month, ready for inspection.
Common Questions Answered
Do I register as a CIS contractor if I am not a construction firm?
Yes. A non-construction business registers as a CIS contractor once it spends more than £3 million on construction in the 12 months since its first payment, under HMRC’s deemed contractor rules. Any business form counts: sole trader, partnership, limited company. Below £3 million of construction spend, and outside construction work itself, CIS contractor duties do not attach.
What is the CIS monthly return deadline?
The CIS monthly return deadline is the 19th of the month following each tax month, and tax months run from the 6th to the 5th. A return covering 6 May to 5 June is due by 19 June. Nil returns are still required in months when no subcontractors were paid.
How are CIS deductions paid to HMRC?
CIS deductions are paid to HMRC together with PAYE tax and National Insurance in one payment per month or quarter. Electronic payments clear by the 22nd; postal payments arrive by the 19th. Late payment attracts interest and penalties.
What happens if a CIS return is late?
A late CIS return attracts £100 at 1 day, £200 at 2 months, and £300 or 5% of the deductions at 6 months, whichever is higher. A further £300 or 5% applies at 12 months, and delays beyond that reach £3,000 or 100% of the deductions. Appeals go through HMRC’s online service within 30 days of the notice.
How Aqua Accounting Can Help
Aqua Accounting runs CIS compliance for contractors as an ICAEW Registered Member Firm of Chartered Accountants, with 13+ years serving North East businesses from a UK-based team in Newcastle upon Tyne.
The work follows the scheme’s own sequence. Registration, including the deemed contractor assessment against the £3 million test. Verification routines that re-check subcontractors after a lapse. Monthly returns filed through the 19th deadline, every tax month, nil months included. Deduction payments aligned with PAYE by the 22nd, penalty appeals lodged inside the 30-day window, and record systems that answer an HMRC review without reconstruction.
Register once, verify every subcontractor, file by the 19th, and the Construction Industry Scheme runs as routine. Speak to Aqua Accounting today to put your CIS duties, from registration to the final monthly return, under management.
Disclaimer:
The information provided in this blog is for general informational purposes only and does not constitute professional advice. While every effort is made to ensure accuracy, Aqua Accounting accepts no responsibility for any actions taken based on this content. You should seek professional advice tailored to your individual circumstances.
Omar Ahmed is an ICAEW Chartered Accountant and the Director of Aqua Accounting, a UK-based accountancy practice providing expert accounting and tax services to individuals, sole traders, and small to medium-sized businesses. As a trusted accountant in Newcastle, he offers expertise in annual accounts, self-assessment tax returns, company accounts, VAT, payroll, bookkeeping, and company formation.
With a strong focus on delivering clear and practical financial advice, Omar helps clients stay compliant while improving their understanding of their finances. Through Aqua Accounting, he works closely with business owners to simplify accounting processes, meet tax obligations, and support informed financial decision-making.