CEST — "Check Employment Status for Tax" — is HMRC's free online tool that gives a view on whether a worker should be treated as employed or self-employed for tax on a particular engagement. It works by asking about the real arrangement and weighing the same factors the courts use: control (how, when and where the work is done), personal service (whether you must do the work yourself or can send a genuine substitute) and mutuality of obligation (an ongoing duty to offer and accept work), alongside others like financial risk and equipment — with no single factor decisive. HMRC will generally stand by a CEST result, provided the answers are accurate and reflect the actual working practices. Who runs that check, though, depends on the client: for public-sector and medium or large private-sector clients, the client decides and issues a Status Determination Statement (SDS); for small private-sector clients, your own intermediary remains responsible.
This is general information about how UK employment-status checks work, not legal or tax advice. CEST and IR35 are UK rules and do not apply in the US or elsewhere; your status depends on your actual working arrangement, and the rules change. Take professional advice before acting on your own situation.
What is the CEST tool and what does it do?
CEST stands for Check Employment Status for Tax, and it is HMRC's own free online tool for working out how a particular engagement should be treated for tax (gov.uk). It asks a series of questions about the work — who controls it, whether you have to do it personally, what financial risk you carry, how you're integrated into the client's business — and returns a view on whether the worker should be treated as employed or self-employed for that engagement. It is built to be used by either side: a contractor checking their own position, or a client deciding the status of someone it engages.
Two things about CEST are easy to get wrong. First, it answers a tax question, not an employment-law one (more on that distinction below). Second, the result is only as good as the inputs. HMRC will generally stand by a CEST outcome where the information given is accurate and reflects the actual or expected working practices — but a careless or contrived set of answers is not something HMRC relies on. In other words, CEST is not a guarantee you can engineer by ticking the convenient boxes; it reflects what you tell it, and HMRC can look behind a result that doesn't match reality. Run honestly against a real arrangement, it's a useful, sourced starting point. Run as a wish-list, it's worth nothing.
What does HMRC look at to decide employment status?
HMRC's check — and the courts' approach behind it — rests on a small set of established factors, weighed together rather than scored individually. The three that do most of the work are control, personal service (the right of substitution) and mutuality of obligation. The table below shows what each points towards.
| Factor | Points to employment | Points to self-employment |
|---|---|---|
| Control (how, when, where) | The client directs how, when and where you work | You decide how the work is delivered |
| Personal service / substitution | You must do the work personally | You have a genuine right to send a substitute |
| Mutuality of obligation | An ongoing duty to offer and accept work | Engaged for a defined task or outcome |
Around these sit other factors — financial risk, who provides the equipment, and how far you're integrated into the client's organisation (do you look like part of the furniture, or like an outside supplier?). The crucial point, stated plainly by HMRC, is that no single factor is decisive: a strong substitution right doesn't automatically settle it, and one employment-like feature doesn't automatically sink it. HMRC and the courts look at the whole picture of how the engagement genuinely operates. This is also why the written contract only helps when it matches the day-to-day reality — if the paperwork and the practice diverge, the practice usually wins.
Who decides your IR35 status — you or the client?
For many contractors this is the part that surprises them: under the off-payroll working rules (IR35), you often don't make the determination yourself. Responsibility depends on the type of client you're working for (gov.uk).
For public-sector clients, and medium or large private-sector clients, the client is responsible for deciding the worker's status. It must then issue a Status Determination Statement (SDS) — a written decision setting out the outcome and the reasons for it — and pass that statement down the contractual chain so everyone involved knows the basis on which the engagement is being treated. These rules took effect for the public sector from April 2017 and for the private sector from April 2021.
For small private-sector clients, the position is different: the responsibility stays with the worker's own intermediary — usually their personal service company — as it did before the reforms. Whether a client counts as "small" is determined under the Companies Act size test; the exact thresholds change and should be confirmed on gov.uk (last updated 26 February 2026) before you rely on them. The practical consequence of the split is worth understanding: a cautious medium or large client may default an engagement to "inside" to limit its own risk, even where the working reality points the other way. Knowing how the factors actually work lets you read an SDS critically and have an evidenced, professional conversation about it — and it sets up the related question of what inside versus outside IR35 actually means for your tax and take-home.
Tax status vs employment-law status — and what you can actually do
A point that trips up even experienced contractors: a CEST or IR35 outcome is about your tax status, not your employment-law status. HMRC may regard someone as self-employed for tax while their status in employment law is something else — the two systems use overlapping but separate tests, and a decision in one doesn't automatically settle the other (gov.uk). So when you talk about "your status", be clear which one you mean: tax status (the CEST/IR35 question) or employment-law status (which governs rights like unfair-dismissal protection). Getting a clean read on either one starts from the same place — the real working arrangement.
That is also where the genuinely useful work lives. Because both checks follow reality, the way to stand on solid ground is to operate as a genuine business: keep real control over how you deliver, work to defined deliverables rather than an open-ended role, carry your own financial risk and equipment, and — where it fits — maintain a genuine right of substitution you could actually exercise. Substitution and control aren't form-filling tricks; they're features of how a real one-person firm runs.
This is the practical ground the IFA's standards and B2B contract framework are built on — helping members evidence that they operate as genuine independent businesses, with a substitution network and contracting standards behind the position rather than just words in a clause. To be absolutely clear, because it matters: IFA membership does not change your status, does not produce an "outside IR35" result, and cannot guarantee any CEST or IR35 outcome. Membership gives you frameworks, standards, support and access — not a status. Your status always depends on the real arrangement. What good structure does is help a genuine position be a defensible one when it's checked.
Frequently asked questions
What is the CEST tool? CEST stands for "Check Employment Status for Tax". It's HMRC's free online tool that gives a view on whether a worker should be treated as employed or self-employed for tax on a particular engagement. It asks about the real working arrangement — control, personal service, financial risk and so on — and returns a result based on those answers. It's a UK tool, used by contractors and clients alike.
How does HMRC check employment status? By weighing established factors together rather than scoring any one in isolation. The main three are control (how, when and where the work is done), personal service or the right of substitution (must you do the work yourself), and mutuality of obligation (an ongoing duty to offer and accept work), alongside others like financial risk and equipment. No single factor is decisive; HMRC looks at the whole working reality.
Who decides if I'm inside or outside IR35? For public-sector clients and medium or large private-sector clients, the client decides and issues a Status Determination Statement — these rules took effect from April 2017 (public sector) and April 2021 (private sector). For small private-sector clients, your own intermediary, usually your personal service company, remains responsible for the decision.
What is a Status Determination Statement? An SDS is the written decision a public-sector or medium/large private-sector client must produce when it determines a worker's status under the off-payroll rules. It sets out the outcome and the reasons for it, and must be passed down the contractual chain so everyone in the engagement knows the basis being applied.
Is the CEST result legally binding? It isn't binding in the abstract — it reflects the inputs you give it. HMRC will generally stand by a CEST result where the information is accurate and reflects the actual working practices, but a careless or contrived set of answers isn't something HMRC relies on. Treat it as a sourced check on a genuine arrangement, not a guaranteed outcome, and take professional advice on your own position.