IR35 Factors Checklist
A guided walkthrough of the main factors HMRC and tribunals weigh for IR35 status — control, substitution, mutuality of obligation and more — for education, not a legal determination.
Leans outside IR35
Your answers score 4 on a scale from -3 (strongly employee-like) to +4 (strongly self-employed-like) — landing in the "outside IR35" zone.
- Factor Score4
This is an educational guide to the main factors HMRC and tribunals weigh (control, substitution, mutuality of obligation, financial risk, equipment, integration, and working for multiple clients) — it is NOT a status determination.
No online tool — including this one and HMRC's own CEST tool — can give a legally binding answer. CEST itself has been widely criticized by tax and legal commentators as oversimplified.
For a real engagement, use HMRC's CEST tool as a starting point and get a professional IR35 assessment — the financial consequences of getting this wrong (unpaid tax, NI, penalties) can be significant.
About the IR35 Factors Checklist
Contractors reach for this before agreeing a new engagement, or when a client's working practices have changed enough that last year's assumptions no longer feel safe. IR35 status isn't decided by a single question — it's built from a handful of factors that HMRC and employment tribunals have weighed in case after case, and this walkthrough puts the main ones in front of you in plain language instead of legal phrasing.
None of the individual factors is decisive on its own; what matters is the overall picture they build together, which is exactly why HMRC's own CEST tool and this checklist both work by combining several answers rather than asking one yes/no question. This tool gives you an indicative lean, not a verdict — think of it as a way to spot which factors are working against you before you commit to a contract structure.
IR35 status touches genuinely sensitive territory — your working relationship with a specific client, named or not. Every answer you give here stays in your browser only; nothing is submitted, logged, or tied to an account, so you can think through your actual working practices honestly.
How it’s calculated
The factors fall into two groups. Employee-like indicators (working under detailed client control, being obliged to accept ongoing work with no genuine right of refusal, and being integrated into the client's organisation as if you were staff) push toward 'inside IR35'. Self-employed-like indicators (a genuine, unrestricted right of substitution, bearing real financial risk, providing your own equipment, and working for multiple clients concurrently) push toward 'outside IR35'.
This checklist weights your answers across those factors and produces an indicative lean rather than a score with legal meaning — case law has repeatedly shown that these factors are weighed together and in context, not simply added up, so a strong showing on one factor can be outweighed by a weak one elsewhere.
Mutuality of obligation and control are generally treated as the two factors courts return to most often, but substitution rights have also proven decisive in several leading cases — which is part of why no automated tool, including HMRC's own CEST, can turn this into a guaranteed answer.
Frequently asked questions
What is IR35 and who does it affect?
IR35 is UK tax legislation aimed at contractors who work through their own limited company but whose actual working relationship with the client resembles employment. If an engagement is caught by it, income from that engagement is taxed broadly as if it were employment income, rather than benefiting from the salary/dividend structure of a limited company.
What's the single biggest factor in determining IR35 status?
There isn't one — tribunals have repeatedly stressed that no single factor is decisive on its own. Control, substitution, and mutuality of obligation tend to carry the most weight, but the full working picture, taken together, is what actually determines status.
Who decides my IR35 status — me, my client, or HMRC?
Under current off-payroll working rules, medium and large private-sector clients (and all public-sector clients) are generally responsible for determining status and issuing a Status Determination Statement; for engagements with small private-sector clients, the contractor's own limited company typically remains responsible.
Is HMRC's CEST tool reliable?
CEST is HMRC's own tool and its outcome is generally accepted by HMRC where the questions are answered accurately, but it has been widely criticised by tax professionals and tribunals for oversimplifying factors like mutuality of obligation. It's a reasonable starting point, not a substitute for a full assessment on a complex engagement.
Can I be inside IR35 on one contract and outside on another?
Yes — IR35 status is assessed per engagement, based on that specific contract's terms and actual working practices, not as a general label attached to you or your company. The same contractor can be outside IR35 on one client's terms and inside on another's.
What happens if I get my IR35 status wrong?
If HMRC later determines an engagement should have been treated as inside IR35 and wasn't, the consequences can include backdated tax and National Insurance, interest, and penalties — which is why a borderline result here is worth following up with a professional assessment before signing.
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