IR35 has a reputation for being impenetrable, and the name doesn't help — it tells you nothing about what it actually does. Strip away the jargon and the underlying question is simple: when you engage someone through their own limited company rather than employing them directly, are they genuinely working like an independent contractor, or are they really working like an employee in all but name? The tax rules follow the reality of the relationship, not what the paperwork calls it.
The question underneath the jargon
If a contractor works to your instructions, at your times, at your premises, using your equipment, integrated into your team like any other staff member, and can't send someone else to do the work in their place — that starts to look like employment, whatever the contract says. If they control how and when the work gets done, could reasonably send a substitute, carry their own business risk, and work for other clients too, that looks like genuine self-employment. IR35 exists to stop the tax advantages of self-employment being used for a relationship that's actually employment in every practical sense.
Why it matters to you, not just the contractor
The important shift for small business owners to know: for engagements with medium and large businesses, it's usually the client — you — who's responsible for assessing the status and can be on the hook for the tax if it's got wrong, not just the contractor's company. Even where the smaller-business exemption applies and the responsibility sits with the contractor, getting caught out by a status dispute further down the line is still disruptive and costly to unwind. It's not a problem you can assume is entirely someone else's.
IR35 doesn't ask what your contract says. It asks what actually happens on a Tuesday — who tells them what to do, and could someone else show up and do it instead.
Getting the working relationship right, not just the paperwork
A contract that says 'self-employed contractor' throughout doesn't protect you if the day-to-day reality looks like employment — HMRC and tribunals look past the wording to how the relationship actually functions. If you want a genuine contractor relationship, and want it to hold up if questioned, build in real independence: let them decide how the work gets done rather than directing every step, allow a genuine right of substitution where practical, avoid folding them into your internal structures and benefits like a de facto employee, and make sure they're genuinely free to work for other clients. If none of that's realistic for the role you need filling, you may simply need an employee, not a contractor — and that's a legitimate, often simpler, answer.
Where this bites hardest
This matters most for the kind of small business that leans on contract or freelance help regularly — agencies bringing in specialist skills project to project, consultancies scaling up for a big engagement, businesses covering a skills gap without a full-time hire. It's worth a genuine, honest look at your working contractor relationships, not just your contract templates, because the templates are rarely where the risk actually lives.
The status determination in practice
For engagements where you're responsible for the assessment, that means actually completing a status determination for the role — not just assuming it's fine because the contractor's been doing similar work elsewhere for years. Do it honestly, using how the role actually operates rather than how you'd like it to look on paper, and keep a record of your reasoning. If HMRC ever queries it, having genuinely thought it through and documented why — even if a determination later turns out to be debatable — puts you in a far better position than never having asked the question at all.
Where owners get caught out without realising
A common trap is letting a genuinely independent contractor relationship drift into something closer to employment over time, without anyone deciding it should. A contractor brought in for a single project ends up working exclusively for you for two years, attending every team meeting, using your email address, effectively indistinguishable from staff — while everyone involved still calls it 'contracting' out of habit rather than accuracy. IR35 status isn't fixed at the start of a relationship; it's worth re-checking periodically, especially for long-running engagements that have quietly grown well beyond their original scope.
The cost of getting it wrong in either direction
It's worth being honest that there are two ways to get this wrong, not one. Treating an inside-IR35 engagement as outside exposes you to the tax and penalties if HMRC disagrees. But the opposite mistake is common too, and quietly expensive in its own way: being so cautious that you push every contractor determination inside IR35 regardless of the actual facts, adding cost and admin to engagements that were genuinely self-employed, and losing good contractors to businesses willing to assess it properly rather than defensively. Blanket policies in either direction usually cost more than doing the assessment role by role.
When to get proper advice
IR35 status isn't always obvious, and getting it wrong has real cost either way — misclassifying an employee as a contractor, or over-cautiously treating a genuine contractor as inside IR35 and losing good people to competitors who assess it correctly. If you regularly engage contractors and haven't had the actual working relationships checked recently, rather than just the contracts, it's a worthwhile hour with an accountant or employment specialist — considerably cheaper than an HMRC dispute after the fact.
Common questions
Is my business small enough to be exempt from assessing IR35 status?
Almost certainly, and the exemption got wider on 6 April 2026. You count as a small client if you meet at least two of three tests: turnover of £15 million or less, a balance sheet total of £7.5 million or less, and 50 employees or fewer. The first two rose from £10.2 million and £5.1 million, moving thousands of UK businesses back out of the regime. If you are small, you do not determine anybody's status — that duty, and the PAYE risk that goes with getting it wrong, stays with the contractor's own limited company. The exemption is not permanent, though: it is measured against your accounts, so a business growing quickly should know which side of the line its next set of figures puts it on.
What is the difference between IR35 and the off-payroll working rules?
They ask the identical question and put the bill in different places. The original IR35 rules, in force since 2000, leave the contractor's own limited company to decide whether the engagement is really employment and to pay the tax if it is. The off-payroll working rules — public sector from 2017, private sector from April 2021 — move both the decision and the liability onto the client, but only where the client is medium or large. Nothing about the underlying employment status test changes; only who carries the risk. Since April 2024 HMRC has also been able to offset tax the contractor and their company already paid against a client's assessment, which removed most of the double-taxation problem that made these rules so feared.
Will HMRC actually find out if I have got a determination wrong?
They might, and the data trail is better than most owners assume — real-time payroll submissions, contractor company accounts, VAT returns and CIS returns all land in the same place, and HMRC has run compliance campaigns targeted sector by sector. An off-payroll enquiry normally opens with a polite information request rather than anything dramatic. The protection that works is not secrecy, it is a status determination you made honestly at the time and can show. Penalties for an inaccurate return turn on behaviour: nothing at all where you took reasonable care, up to 30% where HMRC decides you were careless, and 70% or more where it concludes the error was deliberate. 'We never thought about it' is the worst available answer.
Should I use HMRC's CEST tool?
Yes, as a starting point — HMRC says it will stand by the result provided your answers reflect the actual working arrangements and were given in good faith, which makes a saved CEST output genuinely useful evidence. Check Employment Status for Tax is free on GOV.UK, takes about a quarter of an hour, and produces a printable determination you should keep with the engagement file. Its weaknesses are well documented: it handles mutuality of obligation differently from the courts, and it returns 'unable to determine' in a meaningful minority of cases. Complete it from what happens on an ordinary Tuesday rather than from the contract wording, and treat an outside-IR35 result as evidence rather than armour on any large or borderline engagement.
What do I actually have to give the contractor?
A Status Determination Statement — your conclusion plus the reasons for it — passed to the worker and to every agency in the chain before the work starts. This applies only where you are a medium or large client responsible for the assessment. You must also run a disagreement process: if the contractor or agency challenges the determination, you have 45 days to consider it and reply with either a revised statement or your reasons for standing by the original. The trap worth knowing is procedural rather than technical. If you fail to take reasonable care, or fail to pass the statement down the chain, the tax liability stays with you even where the determination itself was completely correct.
