The Check Employment Status for Tax (CEST) tool is HMRC's free online questionnaire designed to help end clients, agencies, and contractors determine the IR35 status of an engagement. It asks a series of questions about working practices and delivers a determination of inside IR35, outside IR35, or undetermined.
How to use CEST
CEST is available on the GOV.UK website. You answer approximately 15–20 questions about the engagement, covering substitution rights, control, financial risk, and how the worker fits within the client organisation. The process takes around 10–15 minutes if you have a clear understanding of the working arrangements.
Does HMRC stand by the result?
HMRC has stated it will stand by CEST determinations provided the information entered is accurate and reflects the actual working practices. However, this assurance only extends to the specific engagement described. If your actual working practices differ from what was entered, the determination may not protect you.
Known limitations
CEST has been widely criticised by contractor groups and IR35 specialists. It does not adequately consider mutuality of obligation, which is one of the three core IR35 tests. It also tends to deliver a high proportion of "undetermined" results, leaving users without clear guidance. Several tax tribunals have reached different conclusions from CEST on the same set of facts, which undermines confidence in the tool.
Should you rely on CEST alone?
Using CEST is a reasonable starting point, but it should not be your only reference. For engagements where IR35 status materially affects your income, consider obtaining an independent IR35 review from a qualified specialist. These reviews examine your contract and working practices in detail and provide a written opinion that carries more weight than a CEST result.