Answer about your engagement
Answer about the actual day-to-day working pattern, not what the contract says on paper. HMRC and tribunals look at reality, not paperwork.
Verdict
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Factor breakdown
| Factor | Signal |
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How this checker works
IR35 — formally the off-payroll working rules — decides whether HMRC treats your engagement as employment in disguise ("inside IR35") or genuine self-employment ("outside IR35"). The verdict matters because inside-IR35 engagements are taxed like employment: PAYE income tax, employee and employer NI, no expenses, and the company-structure tax efficiency disappears.
HMRC's own tool (CEST) and the case-law tradition both come down to three primary factors:
- Mutuality of Obligation (MOO) — does the client have to offer work and do you have to accept it? Employees do; contractors don't.
- Personal Service — does the client require you specifically, or could you send a competent substitute? Contractors usually can substitute.
- Control — how, when, where, and what work do you do? Employees are told; contractors decide.
Plus secondary factors — financial risk, integration with the client's organisation, equipment, exclusivity, intention.
This tool weights answers by the relative importance UK case law gives each factor. It is not a substitute for HMRC's CEST tool, an IR35 specialist's review, or independent legal advice.
Inside, outside, or borderline?
- Outside IR35: overall pattern looks like genuine self-employment. You pay tax via your own company at the usual contractor rates.
- Inside IR35: overall pattern looks like employment. Tax must be deducted as PAYE.
- Borderline: the factors are mixed. Get a contract review and consider an opinion from an IR35 specialist (Qdos, Kingsbridge, IPSE+) — typical cost £100–£300.
Worked examples
Engagement: A freelance UX designer working on a 6-week branding project. Client agrees the deliverables and the deadline; designer chooses how, where, and when to work. The designer has 3 other clients running concurrently. If the designer was ill, the contract allows them to send a vetted associate. They use their own laptop and tools. Payment is the agreed project fee on completion.
Verdict: Strongly outside IR35. All three primary factors point to self-employment.
Engagement: A contractor developer with a 12-month rolling contract at one financial-services client. They work the client's office hours, attend the daily stand-up, use client-issued kit, follow the client's process. The contract says "no MOO" and "substitution allowed" but in practice the contractor has never refused work and substitution would be refused.
Verdict: Borderline, leaning inside. The paper contract says one thing; the reality says another. A specialist review and probably a re-papered contract are needed.
Engagement: A "contractor" who has worked exclusively at one bank for 4 years, attends all-hands meetings, has a permanent desk, gets a Christmas bonus, can't refuse work, can't send a substitute, uses client equipment, line-managed by a director, no other clients.
Verdict: Inside IR35. This is employment with the tax-efficient label of contracting stripped off the top.
No. CEST is HMRC's official tool — if you use it honestly and accept the verdict, HMRC will stand by it (in most cases). This is a faster informal check based on the same principles. For a real determination, use CEST or get an IR35 specialist review.
For contracts with small private-sector clients (under £10.2m turnover / fewer than 50 employees), you decide. For all public-sector and medium/large private-sector clients, the end client decides under the off-payroll working rules introduced in April 2017 (public) and April 2021 (private).
Your fee is taxed as employment income: PAYE income tax, employee NI, plus the engager pays employer NI on top (often deducted from your gross rate via "umbrella" arrangements). Net take-home typically 20–30% lower than the equivalent outside-IR35 contract.
IR35 specifically applies to contractors working through their own limited company (or via a partnership / intermediary). Sole traders fall under separate employment-status rules — broadly similar tests but a different legal framework.
Does the client have to give you work, and do you have to accept it? Employees have ongoing MOO — your boss can give you any reasonable task and you must do it. Contractors have project MOO only — the client must pay for the agreed work, but can't suddenly ask you to do something different.
Whether you can send someone else (vetted, qualified) in your place to do the work. Genuine self-employment usually allows substitution; employment doesn't. A contract that allows substitution but where in practice it would be refused doesn't save you — tribunals look at reality.
If your verdict here is "Borderline" or you're entering a long engagement, yes. Specialists like Qdos, Kingsbridge, Markel, and IPSE+ review contracts and working practices for £100–£300, often with an insurance-backed opinion you can show your client.
Umbrella companies bypass IR35 by treating you as their employee — you pay full PAYE, employee NI, and the umbrella deducts employer NI from your gross rate. It removes the IR35 risk entirely but it's the same net outcome as being inside IR35 minus the umbrella's margin. Usually only worth it for short inside-IR35 contracts where you don't want to operate your own Ltd.
This quick-check is general guidance, not a binding HMRC determination or legal advice. For any contract material to your income, use HMRC's CEST tool and/or engage an IR35 specialist (Qdos, Kingsbridge, Markel, IPSE+).