IR35 in 2026 — A Plain English Guide for UK Contractors and Their Clients

IR35 — the off-payroll working rules — has been one of the most contentious areas of UK tax for the past two decades. For IT contractors, consultants, engineers, and other professionals who operate through their own limited companies, getting IR35 status wrong can result in a large and unexpected tax bill. For the businesses that hire them, the stakes are equally high under the reformed rules that came into force in 2021.

This guide explains how IR35 works in 2026, who is responsible for determining status, what the financial impact of an inside-IR35 determination is, and what genuine steps you can take to protect your position.

What Is IR35?

IR35 (formally the Intermediaries Legislation, now known as the off-payroll working rules) exists to prevent tax avoidance by people who would, in substance, be employees but instead provide their services through a Personal Service Company (PSC) — typically a limited company — to gain the tax advantages of self-employment.

HMRC's concern is the worker who is effectively permanent staff, works solely for one client, is integrated into the client's organisation, is told how and when to do their work, and uses the client's equipment — but pays themselves through dividends and avoids income tax and NI on a large portion of their earnings.

IR35 legislation applies to such workers and treats their income as employment income for tax purposes, even though it is paid through a company.

Who Decides IR35 Status in 2026?

This depends on the size of the end client:

Large and medium private sector clients: The end client (or agency if there is one in the chain) is responsible for determining IR35 status and issuing a Status Determination Statement (SDS) to the contractor. This has been the rule since April 2021.

Small private sector clients: A small company is one that meets at least two of: turnover under £10.2m, balance sheet under £5.1m, fewer than 50 employees. For small clients, the contractor (through their PSC) remains responsible for determining their own IR35 status. The old rules apply.

Public sector: The end client has been responsible for IR35 determination since April 2017.

The Three Key IR35 Tests

IR35 status is not a single test — it is a holistic assessment of the working relationship based on three primary factors established in case law:

1. Substitution: Does the contract allow you to send a substitute to do the work? And is that right real — meaning the client would accept a qualified substitute? A genuine right of substitution is one of the strongest indicators of being outside IR35. A substitution clause that would only allow a substitute with the client's specific approval is less convincing.

2. Control: Does the client control how, when, and where you work? The more control the client has over your working method and schedule, the more employment-like the relationship. Contractors who set their own hours, decide how to achieve deliverables, and use their own equipment are more clearly outside IR35.

3. Mutuality of obligation: Is the client obliged to offer you work, and are you obliged to accept it? In a genuine self-employed relationship, there is no ongoing obligation on either side beyond the current project. If you are automatically moved from project to project without re-engagement, this suggests employment.

Other factors that HMRC and courts consider include: financial risk (do you personally bear the cost of fixing errors?), integration into the client's organisation, equipment provision, and exclusivity (do you work for multiple clients?).

The Financial Impact of an Inside-IR35 Determination

If a contract is deemed inside IR35, the income from that contract is treated as employment income. The practical effect:

• The income must be paid as salary, not dividends
• Income tax and National Insurance (both employee and employer) are deducted
• The tax-efficient salary plus dividend structure is no longer available for that income

For a contractor earning £80,000 from an inside-IR35 contract, the additional tax versus an outside-IR35 structure might be £15,000 to £25,000 per year. This is why the status determination matters enormously.

HMRC's CEST Tool — How Reliable Is It?

HMRC provides the Check Employment Status for Tax (CEST) tool online. It asks a series of questions about the working arrangement and produces a determination. HMRC has committed to stand behind CEST results provided the information entered is accurate.

However, CEST has been widely criticised for not considering mutuality of obligation (a key legal test) and for producing results that do not always align with case law. Many IR35 specialists regard CEST as a useful starting point but not a definitive answer for complex cases.

IR35Shield, Qdos, and other specialist firms provide more comprehensive status assessments and will defend the determination in the event of an HMRC enquiry.

Practical Steps to Protect Your Outside-IR35 Position

• Ensure your contract reflects the genuine working arrangement — substitution clauses, project-based engagement, no ongoing obligation
• Actually exercise your right of substitution at least once if possible
• Work for multiple clients, even if one is primary
• Use your own equipment where possible
• Have your contract reviewed by an IR35 specialist before signing
• Keep a working practices record — notes of how you actually work day to day
• Consider IR35 insurance — available from several providers and provides legal defence costs in the event of an HMRC enquiry

Frequently Asked Questions