What Is the HMRC CEST Tool?
The CEST tool (Check Employment Status for Tax) is HMRC's free online questionnaire for determining IR35 status. You answer a series of yes/no questions about your working arrangement — supervision, control, substitution, financial risk — and CEST gives you a determination: inside IR35, outside IR35, or "unable to determine".
CEST is available at gov.uk/guidance/check-employment-status-for-tax. It's free, anonymous, and takes around 10-15 minutes. HMRC says it will "stand by" CEST results — meaning they won't pursue you for a different status if you answered honestly.
That sounds reasonable. In practice, the tool has serious problems that mean you shouldn't rely on it as your only assessment.
How CEST Works — and Why It Was Built
HMRC launched CEST in 2017 ahead of the public sector IR35 reforms. The idea: give contractors, clients and agencies a definitive inside/outside determination, backed by HMRC's assurance. Employment status law is messy — it turns on case law accumulated over decades, with no single test being conclusive. A digital tool that codified all of that into structured questions would be genuinely valuable.
The tool was updated in April 2025, but the update changed the user interface only — none of the underlying logic was altered. The same fundamental problems remain.
The Specific Problems with CEST
It Ignores Mutuality of Obligation Entirely
Mutuality of Obligation (MOO) — whether there's an ongoing obligation to offer and accept work — is one of the three fundamental tests courts use to determine employment status. HMRC assumes it exists in every engagement and doesn't ask about it. This assumption was directly challenged by the Court of Appeal in the Atholl House decision in 2022, which made clear that MOO cannot simply be assumed. CEST's logic hasn't been updated to reflect this.
Substitution Is Over-Weighted
CEST places enormous weight on whether a contractor has a contractual right of substitution — to the point where having (or not having) this right effectively determines the outcome in many cases. Real courts don't work this way. Judges assess the contract as a whole, and an unfettered right of substitution in a contract that doesn't reflect real practice carries little weight. CEST can't assess whether the substitution clause is genuine or "window dressing".
It Doesn't Assess Real Working Practices
CEST only looks at the contract and what you input about arrangements. HMRC has consistently stated that in any compliance investigation, they'll look at actual working practices, not just the contract. A CEST result based on contract terms that don't match reality offers minimal protection. The tool cannot assess how work is actually performed day-to-day.
20% of Results Are "Unable to Determine"
One in five uses of CEST returns "unable to determine" — meaning the tool simply can't give you an answer. For a tool whose entire purpose is clarity, this is a fundamental failure. Contractors left with an undetermined result must then seek professional advice anyway, defeating the purpose of using CEST.
It Doesn't Keep Pace with Case Law
IR35 case law has evolved significantly since CEST launched. The Atholl House appeal (2022), the PGMOL Supreme Court decision (2023), and other tribunal cases have refined and in some cases reversed HMRC's own stated positions on what determines employment status. CEST's decision logic has not been meaningfully updated to reflect these developments.
HMRC Won't Always Stand Behind It
HMRC says it will "stand by" CEST results provided the information entered was accurate. But "accurate" is doing a lot of work in that sentence. If HMRC opens a compliance investigation and believes the inputs didn't reflect reality, the CEST result is worthless. There are documented cases of HMRC not honouring CEST results during investigations, even where contractors believed they'd answered honestly.
The April 2025 Update — A Facelift, Not a Fix
On 30 April 2025, HMRC released an update to CEST. There was significant anticipation in the contractor community — the tool hadn't received meaningful changes in years, and pressure from the PAC, the House of Lords, and industry bodies had been building.
The update disappointed almost everyone.
HMRC confirmed explicitly: "There is no change to the underlying technical principles." What changed was the language of some questions to make them easier to understand, some new guidance links, and a new pre-requisite question flow. The logic — the weighting of tests, the omission of MOO, the substitution-heavy approach — remained identical.
Dave Chaplin, CEO of IR35 Shield: "As HMRC have stated, 'There is no change to the underlying technical principles'. So, they've basically just updated the User Guide for a piece of software."
Seb Maley, CEO of Qdos: "If it were forwards, then it wouldn't be the case — as HMRC explained to us — that there is no need to rerun previous assessments. That means that, unfortunately, if you didn't trust CEST yesterday, nothing in this update will convince you to trust it today."
Rebecca Seeley Harris, off-payroll specialist: "The new CEST update is definitely more than a facelift... but there is no change to the logic."
HMRC also confirmed that previous CEST results remain valid — contractors who received an "outside IR35" result before the update don't need to rerun the tool. Which implicitly confirms the logic didn't change.
The Data: Contractors Are Walking Away From CEST
Freedom of Information data obtained in 2025 tells the real story. CEST usage peaked at over 800,000 assessments in 2021/22 — when the private sector off-payroll reforms took effect. By 2024/25, that had fallen to under 140,000 — a decline of over 73%.
HMRC's response was to claim this reflects contractors "familiarising themselves" with the rules. But the sharpest decline happened in 2023/24 to 2024/25 — well after any initial familiarisation period. The more plausible explanation: contractors and clients who tried CEST found it unreliable or unhelpful, and stopped using it.
CEST vs Better Alternatives
| Feature | HMRC CEST | IR35 Shield | Qdos Assessment | Specialist Adviser |
|---|---|---|---|---|
| Free to use | Yes | Freemium | Paid | Paid |
| Considers MOO | No | Yes | Yes | Yes |
| Updated for post-2022 case law | No | Yes | Yes | Yes |
| Provides audit trail | Basic | Detailed | Detailed | Yes |
| HMRC will defend result | Sometimes | With insurance | With contract | Yes |
| Reviews actual contracts | No | Partial | Yes | Yes |
| Result type | Inside/Outside/Unknown | Risk score + determination | Full assessment | Professional opinion |
CEST ignores Mutuality of Obligation and doesn't review your actual contract. For most freelancers, an outside result from CEST alone is not sufficient protection. A specialist contract review costs from £99 and gives you a written IR35 opinion based on your actual documents — the kind of evidence that stands up if HMRC investigates.
When CEST Is — and Isn't — Appropriate
When CEST might still be useful
- Quick initial screening — if you're assessing a large volume of contractors and need a rough first-pass filter
- Clear-cut outside IR35 cases — where substitution is genuinely unrestricted and control is minimal, CEST will likely return outside, and it's a documented starting point
- As a starting point only — run alongside other assessments, not instead of them
When you should not rely on CEST
- Any engagement where MOO is genuinely in question
- Public sector or high-profile engagements where the stakes of a wrong determination are high
- Contracts with nuanced substitution rights or control arrangements
- Contractors seeking insurance cover — most IR35 insurers will not cover on CEST alone
- Any situation where you need professional-grade documentation of your status
- Get a contract review from a specialist — Qdos and Kingsbridge both offer written IR35 assessments from ~£99 that review your actual contract against current case law. See our IR35 contract review checklist for what they look at
- Understand the 3 status tests properly — CEST's core weakness is what it measures and ignores. Our guide to SDC, Substitution and MOO explains each test and how HMRC weighs them in practice
- Pair it with IR35 insurance — if the specialist says outside IR35, get insurance that covers investigation costs and any tax liability. Premiums are typically £200–£500/year. Read about what happens in an HMRC IR35 investigation
- Document your actual working practices — keep records of invoices, working arrangements, substitution in practice, project-based working. HMRC looks at reality, not contracts
- Don't use CEST in isolation — if you do use it, treat it as one input among many, not a definitive answer
- Know your numbers — once you know your status, use the IR35 calculator to model the financial impact at your day rate, or freelanceratecalculator.net to work out what rate you need to charge