Since IR35 reforms took effect across the UK, checking employment status for tax purposes has become a critical step for contractors, clients and recruitment agencies. Determining whether a contract sits inside or outside IR35 affects how tax is paid, how take-home pay is calculated and whether the contractor is viewed as genuinely self-employed in the eyes of HMRC. With penalties increasing and compliance checks becoming more frequent, understanding how to assess IR35 status accurately is more important than ever.

For UK contractors, the uncertainty around IR35 often creates confusion, especially when roles vary from assignment to assignment. Some individuals also rely on compliant payroll providers, such as The Infinity Group, to help ensure they work under arrangements that meet HMRC rules. However, the responsibility for accurate status determination still requires careful review using reliable methods. Below are the most effective and trustworthy ways to check IR35 status in the UK.

Using HMRC’s CEST Tool

One of the most widely used tools for assessing Check IR35 status is HMRC’s Check Employment Status for Tax (CEST) tool. It is freely available and designed to help contractors, clients and agencies determine whether a role sits inside or outside IR35.

CEST asks questions about working practices, including control, substitution, financial risk and mutuality of obligation. Once completed, the tool provides a result that HMRC claims it will stand by, provided the information entered is accurate and reflects actual working conditions.

Despite some criticism about limitations in how the tool interprets certain scenarios, CEST remains a primary reference point because of its direct link to HMRC and its ability to produce a written outcome that organisations can keep on record.

Reviewing Actual Working Practices

While contracts are important, HMRC places greater weight on real working practices. This means how the contractor behaves day-to-day and the level of control the client exercises over the work.

Key questions to evaluate include:

• Does the contractor decide how, when and where to complete the work?

• Can the contractor provide a substitute if they cannot work?

• Does the contractor supply their own tools, equipment or training?

• Is the contractor exposed to financial risk?

• Does the client treat the contractor differently from permanent employees?

Reviewing behaviour and working conditions is one of the most reliable ways to check IR35 status because it reflects the true nature of the engagement, not just what is written in a contract.

Examining Substitution Rights

Substitution is one of the strongest indicators of being outside IR35. If a contractor has an unfettered right to send someone else to complete the work, it suggests they are providing a service rather than working as an employee.

When checking IR35 status, ask:

• Is substitution allowed in the contract?

• Is the right genuine and workable in practice?

• Has substitution ever been used in previous roles?

• Would the client accept a qualified replacement?

A theoretical substitution clause with no practical possibility of use may not hold weight with HMRC. A real, functional substitution right significantly strengthens the case for being outside IR35.

Evaluating Control and Supervision

The level of control a client has over a contractor’s work is central to an IR35 assessment. To be considered outside IR35, a contractor should have a reasonable degree of autonomy.

When checking status, consider:

• Does the client dictate working hours?

• Does the contractor choose the methods and processes used to complete a task?

• Is the contractor supervised or monitored closely?

• Is the contractor integrated into the client’s internal structure?

High levels of supervision or instruction usually point toward inside IR35. Independence and freedom in how work is executed suggest an outside-IR35 arrangement.

Checking for Mutuality of Obligation

Mutuality of obligation (MOO) refers to the expectation that a client must provide continuous work and the contractor must accept it. In a genuine business-to-business relationship, there should be no ongoing obligation.

Reliable checks include:

• Is the contractor hired for a specific project or deliverable?

• Can the contractor decline work or end the contract early?

• Are there expectations of continuous work without renegotiation?

Where MOO is clearly present, HMRC may classify the role as inside IR35. When engagement is project-based with no expectation of ongoing work, it supports an outside-IR35 determination.

Reviewing the Written Contract Thoroughly

A contract remains a key document in determining IR35 status. However, it must reflect actual working practices to be effective.

When checking IR35 status, examine:

• Is the contractor described as providing services rather than being treated like an employee?

• Are clauses about control, substitution and financial risk clear and realistic?

• Are there terms that contradict the day-to-day working reality?

• Does the contract specify deliverables rather than hours?

A well-structured contract that supports genuine independence helps strengthen the argument for being outside IR35.

Seeking a Professional IR35 Review

Another reliable method for checking IR35 status is obtaining a professional review from specialists. Many UK firms offer detailed assessments that consider all aspects of the contract and working practices. This can be especially valuable for contractors working on high-value assignments or long-term projects where compliance risks are higher.

Professional reviewers analyse contracts, compare them with HMRC guidelines and identify areas that need strengthening. Some also provide insurance-backed assessments to offer additional protection.

Contractors working with large payroll providers, such as The Infinity Group, often receive guidance or signposting toward professional IR35 review services to ensure full compliance.

Using Independent IR35 Assessment Tools

Beyond HMRC’s CEST, several private tools exist that offer more nuanced assessments. These tools often include questions about working reality, risk-taking, independence and business structure. They provide a more detailed analysis than CEST and can be used alongside other methods to support a final determination.

Independent tools also give contractors the opportunity to identify weaknesses in their working arrangements and adjust them before HMRC reviews occur.

Understanding Sector-Specific Considerations

Different industries interpret IR35 factors uniquely due to the nature of the work. For example:

• IT contractors may have more autonomy and project-based deliverables.

• Healthcare contractors may face higher levels of supervision.

• Construction workers under CIS arrangements may require additional checks.

• Creative freelancers might have mixed-income structures.

A reliable IR35 assessment considers the norms and expectations within each sector. Understanding how IR35 applies in your specific field ensures that the status check is meaningful and accurate.

Maintaining Documentation and Evidence

Evidence plays a crucial role during HMRC checks. Contractors should keep detailed records, including:

• Copies of contracts

• Emails showing autonomy and control

• Proof of substitution rights

• Evidence of work delivered

• Invoices and financial documents

Maintaining clear documentation strengthens the reliability of IR35 status checks and supports the contractor if HMRC ever challenges the determination.

Conclusion

Checking IR35 status accurately is essential for contractors and organisations across the UK. With HMRC paying close attention to off-payroll working rules, reliable assessments are key to avoiding penalties, unexpected tax bills and disputes. Using HMRC’s CEST tool, reviewing real working practices, examining substitution and control, evaluating mutuality of obligation and obtaining professional reviews help build a strong and defensible conclusion.

For contractors working through agencies or payroll providers such as The Infinity Group, having proper guidance and understanding the criteria ensures they operate safely and with confidence. Accurate IR35 status checks protect income, stability and long-term career prospects in an evolving contracting landscape.