IR35 Explained — Off-Payroll Working Rules for UK Contractors 2026
IR35 — formally known as the off-payroll working rules — is one of the most significant pieces of tax legislation affecting UK contractors and freelancers. Getting it wrong can result in large, unexpected tax bills. This guide explains what IR35 means in 2026, how to work out your status, and the practical steps you can take to protect yourself.
What Is IR35?
IR35 was introduced in 2000 to tackle disguised employment — a situation where a worker operates through an intermediary (usually a personal service company, or PSC) but is, in substance, an employee of the end client. HMRC's concern is that the arrangement allows workers to pay less tax and National Insurance than an equivalent employee.
The name comes from Inland Revenue press release 35, the document that first announced the rules. Today the legislation sits in Chapter 10 of ITEPA 2003 (private sector) and Chapter 8 (public sector).
If IR35 applies to your engagement, you are described as being inside IR35. Your income from that contract is treated as employment income and is subject to PAYE income tax and employee plus employer National Insurance Contributions (NICs). Being outside IR35 means you can continue to take a mix of salary and dividends from your PSC in the normal way — the tax-efficient approach covered in our corporation tax guide.
Who Decides Your IR35 Status?
The rules differ depending on the size of your end client.
Medium and Large Private-Sector Clients (and All Public-Sector Bodies)
Since April 2021, the end client is responsible for making the IR35 determination for private-sector engagements where the client is medium or large. Public-sector bodies have had this responsibility since April 2017. The client must issue a Status Determination Statement (SDS) setting out their conclusion and the reasons for it. The SDS must be passed down the supply chain (e.g., to the agency and to your PSC).
If the client concludes you are inside IR35, the fee-payer (usually the agency paying your PSC) must operate PAYE on your fees before paying you.
Small Private-Sector Clients — The Small Company Exemption
If your end client is a small company, the old pre-2021 rules still apply: your PSC is responsible for deciding its own IR35 status and accounting for any tax due.
A company qualifies as small if it meets at least two of the following three conditions in its most recent financial year:
| Threshold | Limit |
|---|---|
| Annual turnover | Not more than £10.2 million |
| Balance sheet total | Not more than £5.1 million |
| Number of employees | Not more than 50 |
Note that the small company test looks at the client, not your own PSC. Also be aware that connected or associated companies can be aggregated when measuring size, so a subsidiary of a large group is unlikely to qualify as small.
The Three Key Employment Tests
Whether you are inside or outside IR35 ultimately comes down to whether a court would regard the working arrangement as employment if there were no intermediary. Three factors carry the most weight:
| Factor | Points towards outside IR35 | Points towards inside IR35 |
|---|---|---|
| Substitution | You have a genuine, unfettered right to send a substitute to do the work | The client expects you personally to carry out the work |
| Control | You decide how, when, and where the work is done | The client directs what you do and how you do it day-to-day |
| Mutuality of Obligation (MOO) | No obligation on either side once the project ends; the client is not obliged to offer further work | The client regularly offers — and expects you to accept — ongoing work |
Courts and tribunals also consider other factors such as financial risk (do you bear the cost if you have to redo defective work?), whether you provide your own equipment, and whether you are integrated into the client's organisation (a "part and parcel" test).
HMRC's CEST Tool
HMRC provides a free online tool called Check Employment Status for Tax (CEST) at gov.uk/guidance/check-employment-status-for-tax. Medium and large clients often use it to produce their SDS.
CEST is not without controversy — tax professionals have criticised it for failing to consider MOO and for producing inconsistent results in edge cases. HMRC has said it will stand behind a CEST result provided the information entered is accurate and complete, which provides some protection. However, a CEST result is not legally binding.
What Happens If You Are Inside IR35?
For medium/large clients and public-sector bodies, the fee-payer deducts income tax and employee NICs via PAYE before paying your PSC. The fee-payer also pays employer NICs (13.8% in 2026) on top of your gross fee. This is a significant cost — one reason some clients now refuse to engage PSCs at all.
For small clients (where your PSC self-assesses), you must calculate a deemed payment at the end of the tax year, pay the tax and NICs due, and report them on your Self Assessment return. You can deduct a 5% allowance from income to cover administration costs, a salary equivalent to the secondary threshold for NICs, pension contributions, and genuine business expenses.
How to Protect Your Outside-IR35 Status
If you believe a contract is genuinely outside IR35, take the following practical steps:
1. Review Your Contract
Your written contract must reflect the real working arrangements. Key clauses to include:
- A genuine right of substitution (and remove any clause requiring personal service)
- No obligation on the client to offer, or on you to accept, further engagements
- Clear project-based scope of work rather than a rolling job description
- Responsibility clauses placing the risk of defective work on your PSC
Many contractors use a specialist contractor legal firm to review or draft contracts. The cost is usually modest relative to the risk.
2. Ensure the Reality Matches the Contract
HMRC will look beyond the written contract at the actual working practices. If your contract says you can send a substitute but you have never done so, that weakens the substitution argument. Keep evidence such as email trails showing you negotiated the project scope, invoices for equipment you purchased, and correspondence about project deliverables rather than working hours.
3. Obtain an IR35 Review or Insurance
Specialist tax advisers — and some contractor insurance providers — offer IR35 contract reviews and ongoing status opinions. Some policies provide cover for HMRC investigation costs and, in some cases, the tax liability itself if you followed the advice given. This is often referred to as IR35 insurance or tax investigation insurance. For general business insurance considerations as a contractor, see our business insurance guide, which covers professional indemnity and cyber cover alongside EL and PL.
4. Challenge an Incorrect SDS
If a medium or large client issues an SDS placing you inside IR35 and you disagree, you have the right to use the client's client-led disagreement process. The client must respond within 45 days, providing reasons. Keep records of all correspondence. If the process fails, you can ultimately raise a formal dispute with HMRC, though this is rarely necessary if you have engaged constructively from the outset.
IR35 and Umbrella Companies
Some contractors working inside IR35 operate through an umbrella company rather than a PSC. The umbrella employs you directly, operates PAYE on your fees, and pays you a net salary. While this removes the administrative burden of running your own limited company for that engagement, margins are thin and you should compare costs carefully, including the employer NICs that are effectively deducted from your gross rate.
Be wary of umbrella companies that claim to offer unusually high take-home pay — many such schemes have been challenged by HMRC and are listed on the HMRC tax avoidance schemes list.
Summary: Key Points for 2026
- IR35 applies contract by contract — assess each engagement individually.
- For public-sector and medium/large private-sector clients, the client determines your status and must issue an SDS.
- For small private-sector clients, your PSC self-assesses.
- The three main tests are substitution, control, and mutuality of obligation.
- Ensure your written contract and actual working practices are consistent.
- Consider a specialist contract review and IR35 insurance for high-value or long-running contracts.
- If you receive an inside-IR35 SDS you disagree with, use the formal disagreement process promptly.