IR35 Status Checker for UK Contractors
AI Contract Analysis That Beats HMRC's CEST
Executive Summary
In a nutshell
An AI-powered tool that lets UK limited company contractors upload their contract and answer 10 questions about working practices — returning a plain-English IR35 status verdict, a defensibility score, and specific clause-by-clause fixes. HMRC’s own CEST tool has been described as “hopelessly unreliable” by the House of Lords, has a 58% accuracy rate, and has seen a 73% usage collapse. Existing free tools are basic form-fillers. Professional human review costs £125–£250 and takes 3–5 days. This tool delivers an AI-powered equivalent in under 5 minutes for £9/month.
The Story
Meet the user
Marcus is a senior developer who’s been contracting through his limited company for six years. He knows the work, he knows the clients, and he knows he genuinely operates outside IR35 — he sets his own hours, brings his own laptop, and regularly works for three different clients in the same month. But his current engagement is with a large financial services firm, and his project manager keeps referring to “our contractor” in all-hands emails. When his new contract lands in his inbox, he reads through the clauses — Substitution Rights, Mutuality of Obligation, Control — and suddenly he’s not so sure. He runs it through HMRC’s CEST tool. It takes twelve minutes, asks confusing questions about vehicle expenses, and returns: “Unable to determine employment status.” Great.
A contractor friend mentions IR35Clarity — it took him ten minutes and gave him a clause-by-clause breakdown showing exactly which wording in his contract was creating risk, and what to ask his client to change. Marcus uploads his contract PDF, answers questions about how the day-to-day actually works, and gets back a defensibility score of 78/100, a flagged clause around “day-to-day supervision,” and draft replacement wording he can send to his hiring manager. For the first time in weeks, he knows exactly where he stands.
Scores
How does this idea stack up?
7.4/10
800,000 UK limited company contractors, £40M+ TAM, underserved by AI tools. 9,700/month keyword cluster at extraordinarily low competition (0.05–0.19).
CEST 58% accurate, 73% usage collapse, fails to determine 19% of cases. £125+ for human review. Contractors face five-figure HMRC bills for getting this wrong.
Standard web stack + LLM API for contract analysis. Legal accuracy requires careful prompt engineering, but no regulated activity — it’s a risk tool, not legal advice.
April 2026 IR35 threshold changes bring 14,000 more companies into self-determination scope. MTD for Income Tax links IR35 status to mandatory digital records. New contract season is now.
IR35 has existed since 2000 and has survived every government — it’s a perennial contractor concern, not a one-cycle compliance rush.
Solo-buildable in 4–5 weeks. The hard part is prompt engineering for accurate clause analysis. Domain expertise helps but can be built in.
Strongest
Pain
The CEST tool failure is well-documented at the highest levels — House of Lords, IPSE, court rulings. Contractors face five-figure HMRC bills for getting this wrong. The pain is acute, public, and actively seeking a solution.
Watch out
Feasibility
Giving incorrect IR35 advice has real financial consequences for contractors. The product must be positioned as a risk assessment tool, not legal advice. Clear disclaimers are non-negotiable.
Pain Point
The problem
“Getting your IR35 status wrong can be costly — if HMRC investigates and finds you’ve been incorrectly operating ‘outside IR35,’ they can demand all back-paid Income Tax and National Insurance, interest on the outstanding amount, and significant penalties, which can be a financial nightmare potentially destroying the viability of your limited company.”
— ContractorUK forum, widely cited across contractor media
HMRC’s CEST (Check Employment Status for Tax) tool is the official IR35 determination tool, and it’s catastrophically unreliable. An FOI request revealed that CEST gives correct results in only 14 of 24 test cases (58% accuracy). In 7 cases (29%) it gave flat-out wrong answers. The House of Lords described it as “not fit for purpose.” Over an 18-month period, CEST failed to produce any determination in 210,000 cases (19% failure rate), returning “unable to determine” and suggesting contractors “call HMRC” — a spectacularly unhelpful response when you’re trying to sign a contract.
The financial stakes are severe. HMRC IR35 investigations average £50,000–£150,000 in back-tax liability for contractors who’ve been outside IR35 incorrectly. The market for IR35 insurance (Qdos, Kingsbridge) is itself a £50M+ market — that’s how real the fear is. CEST usage peaked at 800,000 assessments in 2021/22 and fell to under 140,000 by 2024/25 — a 73% collapse in three years — yet there is no modern AI-powered individual contractor tool to replace it.
r/ContractorUK is full of “is my contract inside IR35? Here’s the text…” posts where contractors paste their contracts and ask for human review. The demand for specific, contract-level feedback is clear — and no affordable product provides it.
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