Understanding how to check IR35 status is important for contractors, freelancers, recruitment agencies and businesses across the UK. IR35 legislation affects how certain contractors are taxed when they provide services through their own limited company or another intermediary.

Getting an IR35 decision wrong can create unexpected tax liabilities and compliance difficulties. Contractors may face changes to their take-home pay, while businesses may become responsible for deducting Income Tax and National Insurance contributions where the off-payroll working rules apply.

Whether you are a contractor accepting a new assignment or a business hiring external professionals, understanding the process can help you make informed decisions.

In this guide, we explain what IR35 status means, how to check it, which factors matter and how UK businesses and contractors can manage their responsibilities.

What Does IR35 Status Mean?

IR35 is the commonly used name for the UK's off-payroll working rules. These rules are designed to ensure that individuals who provide services through an intermediary, such as a personal service company (PSC), pay broadly similar employment taxes to an employee where the working relationship would otherwise be considered employment.

An IR35 assessment normally produces one of two outcomes:

Inside IR35: The contractor is treated as employed for tax purposes for that particular engagement. Where the relevant off-payroll rules apply, the deemed employer or fee-payer is generally responsible for deducting Income Tax and employee National Insurance contributions and paying employer National Insurance where required.

Outside IR35: The engagement is considered self-employment for tax purposes under the relevant rules. The contractor's intermediary generally remains responsible for its own tax obligations.

It is important to understand that IR35 status is assessed for each engagement. A contractor could have one assignment inside IR35 and another outside IR35, depending on the actual contractual terms and 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.

For contractors, an assessment can help them:

• Understand how an engagement may be taxed.

• Review the financial impact of a contract.

• Identify potentially unsuitable contractual arrangements.

• Discuss working practices with a client.

• Reduce the risk of unexpected tax liabilities.

For businesses, checking IR35 status can help them:

• Understand their responsibilities when engaging contractors.

• Make appropriate employment status decisions.

• Prepare accurate payroll arrangements where required.

• Reduce the risk of tax compliance problems.

• Maintain clear records of status assessments.

A proper assessment should consider the complete working relationship rather than relying only on the job title or the wording of a contract.

How to Check IR35 Status in the UK

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

1. Review the Contract

Start by examining the contract between the contractor's intermediary and the client. Look at the services being provided, responsibilities, payment arrangements, duration and termination conditions.

However, a written contract is only one part of the assessment. The actual working practices must also be considered.

For example, if a contract describes someone as an independent contractor but the client controls their daily activities in a similar way to an employee, the real working arrangement may create an employment status concern.

2. Consider Control

Control is an important factor when assessing employment status.

Consider who decides:

• What work must be completed.

• How the work should be carried out.

• When the work should be performed.

• Where the contractor must work.

A contractor who has genuine independence over how they deliver an agreed service may have different status indicators from someone who works under close client supervision.

No single factor determines the result. Control must be considered alongside the other relevant circumstances.

3. Examine the Right of Substitution

The right of substitution concerns whether a contractor can send another suitably qualified person to complete the work instead of personally carrying it out.

A genuine and workable substitution arrangement may indicate that the contractor is operating independently.

However, simply including a substitution clause in a contract is not enough. The arrangement must reflect the actual agreement and be realistic in practice.

4. Consider Mutuality of Obligation

Mutuality of obligation looks at the commitments between the client and the contractor.

For example, consider whether the client is required to offer ongoing work and whether the contractor must accept it.

A relationship involving continuing obligations can be an important factor when assessing employment status. The full circumstances must still be considered rather than treating this factor as a decision on its own.

5. Review Financial Risk and Business Responsibilities

Genuine businesses often take financial risks when providing services. A contractor may need to correct defective work at their own expense, provide equipment or manage operating costs.

These arrangements can help demonstrate commercial independence, depending on the wider circumstances.

Review whether the contractor is responsible for delivering an agreed result, managing their own business expenses and handling the financial consequences of their work.

Using HMRC's CEST Tool to Check IR35 Status

HMRC provides an online service called Check Employment Status for Tax (CEST). It helps users assess whether an individual should be treated as employed or self-employed for tax purposes and whether the off-payroll working rules apply to an engagement.

The tool can be used by contractors, clients, agencies and other interested parties.

Before using CEST, prepare information about:

• The written or verbal contract.

• The contractor's responsibilities.

• Who controls the work and how it is completed.

• Payment arrangements.

• Substitution arrangements.

• Business expenses and equipment.

• Any relevant employment benefits.

The questions should be answered accurately and reflect the real or expected working arrangements.

HMRC states that it will stand by CEST results where the information supplied is accurate and the result is used in accordance with its guidance. If the working arrangements change, the assessment may need to be reviewed.

You can access the official tool here:

https://www.gov.uk/guidance/check-employment-status-for-tax

Who Is Responsible for Making an IR35 Decision?

Responsibility depends on the type and size of the client.

For public sector organisations and medium or large private sector clients, the client is generally responsible for determining the contractor's employment status for tax purposes when the off-payroll working rules apply.

These clients should take reasonable care when making their decision and provide a Status Determination Statement (SDS) explaining the outcome and the reasons behind it.

For a small private sector client, responsibility generally remains with the contractor's intermediary, such as their personal service company.

Recruitment agencies and other organisations in the labour supply chain may also have responsibilities, particularly where they act as the fee-payer.

Contractors should therefore establish who is responsible for the decision before accepting an assignment.

Common IR35 Mistakes to Avoid

Businesses and contractors can make mistakes when assessing IR35 status. Some common examples include:

Relying only on contract wording: A contract may describe someone as self-employed, but the actual working relationship is equally important.

Ignoring changes in working practices: If responsibilities, supervision or working arrangements change, the original assessment may no longer reflect the engagement.

Assuming every contract has the same status: IR35 applies on an engagement-by-engagement basis. One assessment should not automatically be used for every client.

Failing to keep records: Businesses should retain relevant contracts, assessments, supporting evidence and Status Determination Statements where required.

Using incorrect information in CEST: Inaccurate answers can produce an unreliable result. Always check the facts before completing the assessment.

Avoiding these mistakes can help improve the quality of IR35 decisions and support better tax administration.

How The Infinity Group Supports UK Businesses

Managing contractor arrangements, payroll responsibilities and tax compliance can be challenging for growing businesses. Understanding IR35 is particularly important for organisations that regularly work with freelancers, consultants and contractors.

The Infinity Group provides business-focused services and information for organisations looking to manage their business and financial responsibilities. Businesses can visit its website to explore the available services and find out more about the support relevant to their needs.

Visit https://theinfinitygroups.com/ to learn more about The Infinity Group.

Taking a careful approach to contractor assessments, maintaining accurate records and seeking appropriate professional guidance can help businesses manage their responsibilities more effectively.

Final Thoughts

Knowing how to check IR35 status is essential for UK contractors and businesses that use intermediary arrangements. A reliable assessment should consider the contract, actual working practices, control, substitution, mutuality of obligation and financial responsibilities.

HMRC's CEST tool can provide useful guidance, but the information entered must accurately reflect the engagement. Businesses should also understand whether they or the contractor's intermediary are responsible for making the status decision.

By reviewing contracts carefully, keeping supporting records and checking working arrangements regularly, contractors and businesses can make more informed decisions and manage IR35 responsibilities with greater confidence.