Understanding how to check IR35 status is important for contractors, recruitment agencies and businesses across the UK. IR35 legislation, also known as the off-payroll working rules, determines whether a contractor should be treated as employed or self-employed for tax purposes when providing services through an intermediary, such as a personal service company.

Getting IR35 status wrong can lead to unexpected tax liabilities, financial penalties and compliance difficulties. For contractors, an incorrect assessment may affect take-home pay and the way they manage their business. For companies, it can create additional responsibilities and potential costs.

Whether you are a contractor starting a new assignment or a business engaging independent professionals, understanding the rules can help you make informed decisions.

This guide explains how to check IR35 status, which factors HMRC considers and how UK businesses can manage their responsibilities.

What Is IR35?

IR35 is UK tax legislation designed to prevent individuals from avoiding employment taxes by providing services through an intermediary when their actual working relationship is similar to employment.

For example, a contractor may operate through a limited company and provide services to a client. If the contractor would have been considered an employee for tax purposes had they worked directly for that client, the engagement may fall inside IR35.

There are two main outcomes:

Inside IR35: The contractor is treated as employed for tax purposes for that particular engagement. Income Tax and employee National Insurance are generally deducted through PAYE by the responsible fee-payer.

Outside IR35: The engagement is treated as self-employment for tax purposes under the off-payroll rules. The contractor's intermediary generally remains responsible for its tax obligations.

IR35 status is assessed on an engagement-by-engagement basis. A contractor can have one contract inside IR35 and another outside IR35, depending on the actual working arrangements.

Why Is It Important to Check IR35 Status?

Checking IR35 status before starting an assignment can help contractors and businesses understand their tax responsibilities.

1. Avoiding Unexpected Tax Liabilities

An incorrect employment status assessment can result in unpaid Income Tax and National Insurance contributions. Checking the position carefully helps reduce the risk of unexpected liabilities.

2. Understanding Take-Home Pay

A contractor's IR35 status can affect how payments are processed and how much money they receive after deductions.

Understanding the likely tax treatment before accepting an assignment makes financial planning easier.

3. Supporting HMRC Compliance

Businesses that fall within the off-payroll working rules must take reasonable care when determining employment status. A clear assessment and suitable records can help demonstrate compliance.

4. Protecting Business Relationships

Clear communication between contractors, agencies and end clients can reduce disagreements about employment status, payment arrangements and contractual responsibilities.

How to Check IR35 Status in the UK

There are several practical steps contractors and businesses can follow when checking IR35 status.

Step 1: Review the Contract

Start by examining the written agreement between the contractor's intermediary and the client, along with any relevant agreements in the supply chain.

Look for details about responsibilities, working hours, supervision, payment arrangements and the services being provided.

However, a contract alone does not determine IR35 status. The actual working relationship must also be considered.

Step 2: Examine the Right of Substitution

One important factor is whether the contractor can provide a suitably qualified replacement to complete the work.

A genuine and practical right of substitution may support a conclusion that the contractor is operating independently. However, the wording of a contract is not enough if substitution is not realistically permitted or used in practice.

Step 3: Consider Control

Control is another important factor when assessing employment status.

Consider who decides:

• How the work must be completed.

• When the contractor works.

• Where the services are delivered.

• Which tasks and responsibilities the contractor must undertake.

A high level of client control may indicate an employment-like relationship, although the full circumstances must be considered.

Step 4: Assess Mutuality of Obligation

Mutuality of obligation considers whether the client is expected to provide work and whether the contractor is expected to accept and complete it.

The nature of the obligations during the assignment can help determine whether the relationship resembles employment or an independent business arrangement.

Step 5: Review Other Employment Status Factors

Other relevant factors may include financial risk, provision of equipment, integration into the client's organisation and whether the contractor operates independently.

No single factor automatically determines IR35 status. The overall picture of the working relationship is what matters.

Using HMRC's CEST Tool to Check IR35 Status

HMRC provides an online tool called Check Employment Status for Tax, commonly known as CEST.

The tool helps workers, clients and agencies assess whether an individual should be treated as employed or self-employed for tax purposes.

To use CEST effectively, prepare information about:

• The contract and services being provided.

• The contractor's responsibilities.

• Who controls the work and how it is completed.

• Working hours and location.

• Payment arrangements.

• Substitution arrangements.

• Relevant expenses and benefits.

HMRC states that it will stand by CEST results where the information supplied is accurate and reflects the actual or expected working arrangements.

However, CEST cannot replace a proper understanding of the contract and working practices. If the information is incomplete or circumstances change, the assessment may need to be reviewed.

Contractors and businesses should keep a copy of the answers and outcome for their records.

Who Is Responsible for Checking IR35 Status?

Responsibility depends on the type of client and the engagement.

Public Sector Organisations

Public sector clients are generally responsible for determining the employment status of contractors providing services through their own intermediaries.

Medium and Large Private Sector Businesses

Medium and large private sector clients are generally responsible for making the status determination and providing a Status Determination Statement (SDS).

The statement should explain the conclusion and the reasons behind it.

Small Private Sector Businesses

Where a contractor provides services through their own intermediary to a qualifying small private sector client, the contractor's intermediary is generally responsible for deciding whether the original IR35 rules apply.

Businesses should check the applicable size criteria and any relevant exceptions rather than assuming they qualify as small.

What Is a Status Determination Statement?

A Status Determination Statement is a written decision explaining whether an engagement falls inside or outside the off-payroll working rules.

Where the client is responsible for the determination, the statement should:

• Clearly explain the employment status decision.

• Include the reasons supporting that decision.

• Be provided to the worker and the relevant organisation in the contractual chain.

• Reflect the actual working arrangements.

The client must take reasonable care when making the assessment. If the contractor disagrees with the outcome, they can use the client's disagreement process to raise their concerns.

Common IR35 Mistakes Businesses and Contractors Should Avoid

Even experienced contractors and businesses can make mistakes when assessing employment status.

Common problems include:

• Relying only on contract wording.

• Assuming every limited company contractor is outside IR35.

• Ignoring actual working practices.

• Using incorrect information in the CEST tool.

• Failing to provide a Status Determination Statement when required.

• Not reviewing a decision when working arrangements change.

• Treating every contractor engagement as having the same IR35 outcome.

A careful, evidence-based approach can help businesses avoid these problems and maintain better records.

How The Infinity Group Can Support UK Businesses

Managing tax responsibilities, payroll processes and business compliance can be challenging for organisations working with contractors.

The Infinity Group provides business-focused information and support through its website, helping businesses explore services relevant to their financial and operational requirements.

Businesses looking to improve their administration, understand their compliance responsibilities or explore available business support can visit The Infinity Group.

Maintaining clear contracts, accurate records and suitable professional guidance can help organisations manage contractor arrangements more effectively.

Conclusion

Knowing how to check IR35 status is essential for UK contractors, recruitment agencies and businesses engaging professionals through intermediaries.

The assessment should consider the contract and the actual working relationship, including control, substitution, mutuality of obligation and other relevant employment status factors.

HMRC's CEST tool can help, but accurate information and proper record keeping remain essential. Businesses must also understand who is responsible for making the determination and issuing a Status Determination Statement.

By reviewing each engagement carefully and seeking professional advice where necessary, contractors and businesses can make better decisions, reduce compliance risks and manage their tax responsibilities with greater confidence.