Understanding CEST: HMRC’s employment status tool for IR35

The Check Employment Status for Tax (CEST) is an online tool introduced by HMRC to help determine an individual’s employment status for tax.

For contractors working through their own limited companies, it is commonly used to assess whether an engagement falls inside or outside IR35. Here, we look at how the tool works, who uses it and what its result means in practice.

Who determines the IR35 status of a contract?

Who is responsible for determining IR35 status depends on the size and type of organisation using the contractor’s services.

Under the off-payroll working rules introduced in the public sector in April 2017 and extended to medium and large private sector organisations in April 2021, the end client is normally responsible for determining the contractor’s employment status for tax.

The client must take reasonable care when reaching its decision and issue a Status Determination Statement (SDS), setting out whether the engagement falls inside or outside IR35 and explaining the reasons for that conclusion.

If the engagement is inside IR35, the deemed employer is responsible for operating PAYE and accounting for the relevant Income Tax and National Insurance. In a straightforward contractual chain, this will usually be the fee-payer immediately above the contractor’s limited company.

These off-payroll rules are contained in Chapter 10 of Part 2 of the Income Tax (Earnings and Pensions) Act 2003.

Where the contractor provides services to a small private sector client, responsibility normally remains with the contractor’s own limited company under the original IR35 rules in Chapter 8.

For more information, see our plain-English guide to IR35.

When was the CEST tool introduced?

HMRC introduced the CEST tool in 2017 to coincide with the rollout of the Off-Payroll rules for public sector organisations. An update was released in November 2019 prior to the private sector rollout, with smaller refinements made since then. The wording of the tool was updated again in April 2025 as part of a wider HMRC tax simplification programme.

How does the CEST tool work?

CEST is a digital aid designed to help determine employment status. It asks a series of questions about the contract and the day-to-day working arrangements before producing its result.

You can access HMRC’s Check Employment Status for Tax tool on GOV.UK.

The questions cover areas such as control, substitution, financial risk and the wider relationship between the contractor and the client.

Once completed, CEST will normally provide one of the following outcomes:

• Employed for tax purposes for this work — broadly equivalent to an inside IR35 result;
• Self-employed for tax purposes for this work — broadly equivalent to an outside IR35 result; or
• Unable to make a determination.

An “unable to make a determination” result does not mean that the engagement must be treated as inside IR35. It means the answers entered have not allowed the tool to reach a clear conclusion, and further advice or a more detailed review may be needed.

One limitation of the tool is that it relies on a structured questionnaire. There is no place to add your comments or nuances related to a particular engagement. This means the result won’t reflect every aspect of a complex contract or working relationship.

Will HMRC stand by the CEST result?

HMRC says it will stand by a result produced by CEST, provided the information entered is accurate, remains accurate and the tool has been used in accordance with its guidance.

The answers must reflect what happens in practice as well as the written contract. If the working arrangements change, the assessment should be completed again.

Will I receive confirmation of my IR35 result from CEST?

CEST allows you to review the answers and save or print the completed result. You should retain a copy, together with any documents used to support the answers entered.

There are several tools available – which one should I use?

There are a number of commercial status assessment systems available online. Some ask for more detail than others, but there is no one-size-fits-all approach.

CEST is HMRC’s official tool and is often used by larger organisations making determinations under the Chapter 10 rules. Other services may offer a more detailed assessment or include a professional review of the contract and working practices.

Whichever tool is used, the accuracy of the result can only ever be as reliable as the information entered into it. The answers should reflect the reality of how the contract is carried out, not simply repeating the clauses contained in the contract.

Interestingly, Freedom of Information data published by HMRC show CEST usage has fallen significantly in recent years, from more than 800,000 assessments in 2021/22 to fewer than 140,000 in 2024/25.

The figures suggest that CEST is being used less frequently than during the early years of the private sector reforms, although HMRC has not attributed a specific reason for the decline.

For further information, including an answer to the question “How reliable is CEST in practice?”, see our IR35 status rules FAQ guide.

Have you had your latest contract reviewed?

Where the end client is responsible for determining your IR35 status, you may wonder why you would need to have the contract reviewed separately.

Although CEST can be useful, its result depends on the information entered and how the questions are answered. It may not provide a clear result in every case or give a complete picture of a more complicated engagement.

A professional IR35 review service will consider how the contractor provides their services in reality, and whether the contractual terms match the genuine working practices.

This level of attention should help identify potential problems which can never be identified via an online questionnaire.

A professional contract review takes longer than completing CEST, but it also provides a far more detailed assessment of both the contract and the actual working arrangements. The cost is often modest compared with the potential financial consequences of an incorrect IR35 determination, and it can provide valuable peace of mind before a contract begins.

Would you still like some advice on IR35? Speak to one of our experienced accountants, who can help with questions about IR35 and the off-payroll working rules. Complete our request a call back form and an accountant will contact you at a convenient time.