CEST Explained: How to Check Your IR35 Status (and Its Limits)

If you’ve researched IR35, you’ll have come across CEST — HMRC’s official status-checking tool. It’s free, quick, and widely used, but it’s far from the final word. Here’s how it works and how much to trust it.

What is CEST?

CEST stands for Check Employment Status for Tax. It’s HMRC’s free online tool that gives an indicative view of whether a contract falls inside or outside IR35 (or whether someone is employed or self-employed for tax generally).

You answer a series of questions about the engagement, and CEST returns one of:

• Outside IR35 (self-employed for tax)
• Inside IR35 (employed for tax)
• Unable to determine

It’s used by end clients, recruitment agencies and contractors as part of assessing off-payroll status.

How to use it

CEST asks about the things that decide IR35 status:

• Substitution — can you send someone else to do the work?
• Control — does the client decide how, when and where you work?
• Financial risk — do you risk your own money?
• Equipment, integration and other factors

The crucial point: your answers must reflect the real working relationship, not the ideal one. Garbage in, garbage out — an “outside” result based on optimistic answers won’t protect you if your actual practices look like employment. We explain those tests in IR35 explained.

How much does the result count?

HMRC says it will stand by a CEST result — provided the information is accurate and matches reality. So a well-evidenced CEST outcome carries weight.

But there are real limitations:

• It returns “unable to determine” in a meaningful share of cases, giving no clear answer.
• It’s widely criticised for not properly testing mutuality of obligation — one of the key IR35 factors — which means it can give an “outside” result that a deeper analysis might question.
• It only reflects the answers you give, so it’s only as good as your understanding of your own working practices.

Don’t rely on CEST alone

Because of these limits, CEST is best treated as a starting point, not a verdict. Sensible contractors and clients:

• Run CEST and review the actual contract and working practices
• Keep the evidence that supports an outside-IR35 position
• Get a professional IR35 review for borderline or high-value contracts

This matters because the cost of a wrong “outside” determination is a backdated tax bill if HMRC successfully challenges it later.

Get a status you can stand behind

A CEST printout on its own is thin protection. What actually keeps you safe is a status that reflects how you really work, backed by evidence — and pay structured correctly for that status. Our accountants for contractors review your contracts and working practices, help you assess and document your IR35 position properly (beyond just CEST), and structure your pay efficiently where you’re legitimately outside. If you’re consistently inside, we’ll help you weigh up an umbrella company instead.