Comprehensive Guide for Contractors: Understanding CIS and Tax Obligations

Contractors working in the construction industry or other sectors where the Construction Industry Scheme (CIS) applies. This page provides practical guidance on CIS deductions and compliance, along with risks to be aware of.

A clear explanation of how CIS works, what contractors need to know about deductions, reclaiming overpaid CIS, and avoiding penalties for non-compliance.

Failing to comply with CIS obligations can result in significant penalties, delays in payments, and a higher tax burden. Understanding the scheme is crucial for contractors to stay compliant and avoid unexpected costs.

How does the Construction Industry Scheme (CIS) work for contractors?

The Construction Industry Scheme (CIS) requires contractors to deduct tax at source from payments made to subcontractors. These deductions are then paid to HMRC. Depending on the subcontractor’s status, the rate of deduction can vary:

  • 20% for registered subcontractors – the standard rate of deduction.
  • 30% for unregistered subcontractors – applied to subcontractors who are not registered under CIS.
  • 0% (Gross Payment Status) – available to subcontractors who meet specific criteria and are approved by HMRC to receive payments gross, without deductions.

If deductions exceed what is owed, subcontractors can reclaim overpaid CIS through their Self-Assessment tax return.

What happens if you don’t comply with CIS?

Contractors and subcontractors who fail to comply with CIS obligations risk the following:

  • Penalties for late registration or missed payments: Contractors who do not register with HMRC or fail to make timely deductions may face fines and interest charges.
  • Late filing penalties: Subcontractors who fail to submit required CIS documents on time can incur additional penalties from HMRC, increasing the tax burden and administrative work.
  • Non-compliance risks: Businesses that fail to operate CIS correctly may also be subject to audits or further scrutiny by HMRC, potentially leading to reclassification of workers and backdated tax liabilities.

HMRC’s approach is strict, and contractors must ensure their payments and paperwork are accurate to avoid these costly errors. Learn more about CIS registration and your obligations on the official HMRC CIS guidance page.

Common mistakes contractors make under CIS

Contractors often overlook key areas when dealing with CIS. Some of the most common mistakes include:

  • Failing to check whether subcontractors are registered with HMRC under CIS.
  • Not verifying the subcontractor’s gross payment status.
  • Not submitting the monthly CIS returns on time, resulting in late penalties.
  • Incorrectly applying the deduction rates or missing necessary documentation.

Correcting these mistakes can be costly, but they are preventable with careful attention to detail and a clear understanding of CIS rules.

In practice: what contractors need to know

In practice, many contractors encounter difficulties with CIS because of confusion around which deductions apply, especially when working with new subcontractors or unfamiliar projects. We regularly see subcontractors who think they are working under gross payment status but are actually subject to 20% deductions. Getting it wrong can result in payment delays or unexpected tax liabilities, making it crucial to check your subcontractor’s status regularly and stay on top of paperwork.

Local support for contractors

If you’re a contractor based in Kingston upon Thames or nearby areas such as Tolworth and Chessington, experienced accountants at CIGMA Accounting can help you stay on top of your CIS obligations. We support contractors and businesses with CIS registration, accurate deduction calculations, and timely submissions, helping ensure compliance is maintained and issues are dealt with before they escalate.

Review your CIS status and avoid penalties

If you are unsure whether your CIS status is correct — or if you need help reviewing your deductions, reclaiming overpaid CIS, or ensuring your compliance with HMRC — it’s important to act now. A short review can save you significant tax liabilities, penalties, and administrative costs.

Need Help With CIS Compliance for Your Construction Business?

The Construction Industry Scheme (CIS) sets out specific rules for how contractors and subcontractors must handle tax deductions, verify registrations, file monthly returns and avoid HMRC penalties. Mistakes can lead to costly fines or compliance issues, so having specialist guidance ensures your CIS reporting and deductions are handled correctly.

Speak to a CIS Tax Specialist

Trusted guidance from London-based accountants, focused on accuracy, clarity, and compliance. 


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CIGMA Accounting
CIGMA Accounting Ltd is a forward-thinking accounting and tax firm based in London, dedicated to delivering high-quality compliance, tax planning, and business advisory services to entrepreneurs, landlords, and growing SMEs. With offices in Wimbledon and Farringdon, we combine local expertise with a tech-driven approach to simplify accounting. Our services include corporation tax filing, VAT compliance, HMRC investigation support, R&D tax credit claims, capital allowances optimisation, and bookkeeping automation. What sets CIGMA apart is our ability to blend traditional accounting rigour with AI-powered systems that reduce errors, save time, and provide real-time financial insights. Our team ensures that every client - from startups to high-net-worth individuals - receives a bespoke solution aligned with their growth goals. Whether you need strategic tax planning, help with HMRC disclosures, or a full outsourced finance function, CIGMA Accounting delivers clarity, compliance, and confidence.
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