Tax & Self-Employment

IR35 Explained — Off-Payroll Working Rules for Contractors (2025 Guide)

26 May 2025 ⏱ 12 min read 🇬🇧 England & Wales Last reviewed: May 2025

IR35 — officially known as the off-payroll working rules — is one of the most debated and misunderstood areas of UK tax law. For contractors working through a limited company, getting it wrong can mean a tax bill worth tens of thousands of pounds. This guide cuts through the jargon and explains who IR35 applies to, how to determine your status, what the rules mean for your take-home pay, and how to protect yourself from an HMRC investigation.

What Is IR35?

IR35 is a piece of anti-avoidance tax legislation — introduced in 2000 — designed to ensure that workers who are functionally employees but work through an intermediary (typically a personal service company or limited company) pay broadly the same income tax and National Insurance contributions as employees doing the same job. The name comes from the HMRC press release number that originally announced the legislation: Inland Revenue 35.

The problem IR35 was designed to address is sometimes called "disguised employment." A worker who would otherwise be an employee sets up a limited company, contracts their services to the client through that company, and extracts money as dividends rather than salary — paying significantly less tax and NI as a result. IR35 says: if you would be an employee if the intermediary did not exist, you must pay tax as if you were an employee.

IR35 does not prevent you from working through a limited company. It determines how the income is taxed. If you are "inside IR35," the income from that contract is treated as employment income and taxed at income tax and NI rates. If you are "outside IR35," you remain a genuine contractor and can continue to extract profits through a more tax-efficient salary-and-dividends structure.

Who Does IR35 Apply To?

IR35 applies to workers who provide their services through an intermediary — usually a personal service company (PSC) or limited company they own and control — rather than directly as an employee or sole trader. It is most commonly relevant to IT contractors, management consultants, engineering contractors, locum doctors and lawyers, and other professionals who contract their services to clients on a project or fixed-term basis.

IR35 does not apply to sole traders, partnerships, or umbrella company workers (who are already treated as employees for tax purposes). If you are self-employed and invoice clients directly without a limited company structure, IR35 is not relevant to you — though separate employment status rules may determine whether you are genuinely self-employed.

Inside IR35 vs Outside IR35 — What Does It Mean?

🔴 Inside IR35

Tax treated as employment income
Income tax + employee NI deducted at source
Employer NI also payable (by fee-payer)
Limited tax-efficient dividend extraction
No Apprenticeship Levy offset
Higher effective tax rate — often 40–50%+

🟢 Outside IR35

Genuine contractor / self-employed
Take income as salary + dividends
Corporation tax at 25% (or 19% for small profits)
Dividend tax at lower rates
Significantly more tax-efficient
Effective rate often 25–35%

Use our IR35 Take-Home Pay Calculator to compare your net income inside and outside IR35 based on your contract rate.

The Off-Payroll Working Rules — Who Determines IR35 Status?

Before April 2017, it was entirely the contractor's own company that decided whether IR35 applied. Contractors (understandably) tended to conclude they were outside IR35, and HMRC's enforcement was minimal. This changed significantly with the introduction of the off-payroll working rules, introduced in stages:

Public Sector — April 2017

From April 2017, public sector clients (NHS trusts, central government departments, local councils, universities, etc.) became responsible for determining the IR35 status of contractors they engaged. If the client decided the contractor was inside IR35, the fee-payer (usually the agency) became responsible for deducting income tax and National Insurance before paying the contractor's limited company.

Private Sector — April 2021

From 6 April 2021, the same rules were extended to medium and large private sector clients. A "medium or large" client is one that meets at least two of the following: turnover over £10.2 million, balance sheet total over £5.1 million, and more than 50 employees. Small private sector clients are exempt — contractors working for genuinely small businesses still determine their own IR35 status.

The Key Tests — How IR35 Status Is Determined

There is no single definitive test for IR35 status. HMRC and the courts look at the overall picture of the working relationship, taking into account all relevant factors. The key tests — established through decades of employment status case law — are:

1. Substitution

Can you send a substitute to do the work in your place? A right of substitution — particularly an unrestricted right to substitute any appropriately skilled person — is one of the strongest indicators of genuine contractor status. If the client insists on personal service and would refuse a substitute, that points towards employment. The right must be genuine, not just a contractual clause inserted to defeat IR35 — HMRC looks at whether the right is actually exercised or capable of being exercised in practice.

2. Control

How much control does the client exercise over how, when, and where you work? Employees are typically directed by their employer in all these respects. A genuine contractor has significant autonomy over how they carry out the work and may set their own hours, work remotely, and choose their own methods. If the client dictates every aspect of how you work, that points towards disguised employment.

3. Mutuality of Obligation

Is there an obligation on the client to offer work and on you to accept it? In an employment relationship, there is typically an ongoing obligation on both sides. A genuine contractor is engaged for specific projects and has no expectation of being offered further work when a project ends. If there is an expectation on both sides that the relationship will continue indefinitely, that points towards employment.

4. Other Factors

Additional factors considered include: financial risk (does the contractor bear financial risk if they do the job badly or more slowly than expected?), provision of equipment, exclusivity, integration into the client's organisation, length of engagement, and whether the contractor is in business on their own account (do they have multiple clients, their own premises, employees?).

The CEST Tool — HMRC's Check Employment Status for Tax

HMRC provides a free online tool — Check Employment Status for Tax (CEST) — at gov.uk to help determine IR35 status. If CEST gives an "outside IR35" result and the information entered was accurate and the working practices genuinely reflect what is in the contract, HMRC will stand by that result in an investigation.

However, CEST has been widely criticised for producing inaccurate results, particularly because it does not include any direct questions about mutuality of obligation — one of the key tests under employment law. The courts have repeatedly found workers to be employees (inside IR35) in cases where CEST would have given an outside result. CEST is a useful starting point but should not be the sole basis for an IR35 assessment, particularly for higher-value or longer contracts.

Status Determination Statements

When a medium or large private sector client makes an IR35 determination, they are required to provide you with a Status Determination Statement (SDS) setting out their conclusion and the reasons for it. If you disagree with the SDS, you have the right to use the client's disagreement process to challenge it. The client must respond to the challenge within 45 days. If they fail to do so, responsibility for the unpaid tax liability shifts back to the client — making this process worthwhile even if you do not expect to win the challenge.

Blanket Determinations — Are They Legal?

Some clients responded to the April 2021 changes by issuing blanket "inside IR35" determinations for all contractors, or by refusing to engage contractors through PSCs at all, forcing everyone through umbrella companies. HMRC has been clear that blanket determinations are not compliant with the off-payroll rules — status must be determined on a contract-by-contract basis. Contractors who receive a blanket determination have strong grounds to challenge it via the SDS disagreement process.

Beware of "zero rights employees": Being assessed as inside IR35 does not make you an employee for employment law purposes. You pay tax as an employee but receive none of the employment rights — no sick pay, no holiday pay, no redundancy pay. Many contractors end up in this worst-of-both-worlds situation. If this is your position, you may want to consider whether contracting via an umbrella company would give you any additional rights.

Umbrella Companies — Are They a Solution?

Many contractors working inside IR35 or for public sector clients have moved to umbrella companies. An umbrella company employs you directly, paying you through PAYE after deducting tax and NI, and charging the client a mark-up on your rate to cover employer's NI and their admin fee. This simplifies the tax position — you receive a payslip like any other employee — but the cost of the employer's NI (13.8% on earnings above the secondary threshold) is typically absorbed by your day rate, significantly reducing your net income.

The umbrella company market has been plagued by disguised remuneration schemes that claim to deliver "more take-home pay" through loans, annuity structures, or similar arrangements. HMRC and HM Treasury have taken a hard line against these schemes, and contractors who have used them can face significant tax demands years later. If an umbrella company promises take-home pay significantly above what PAYE would produce, that is a major warning sign.

Protecting Yourself — Practical Steps

Get your contract reviewed — an IR35 specialist solicitor or accountant should review your contract before you start work to ensure it accurately reflects genuine contractor working practices, not employment.
Ensure working practices match the contract — a contract that says you have a right of substitution is worthless if no substitution is ever possible in practice. Your actual day-to-day working must match what the contract says.
Obtain an IR35 insurance policy — specialist insurers offer "IR35 investigation insurance" that covers the cost of an HMRC investigation and any tax liability found, provided your status assessment was reasonable. This is relatively affordable and provides significant peace of mind.
Keep records of each contract — retain copies of all contracts, SDS statements, and any documentation of your working practices for at least seven years, as HMRC can open an investigation going back six years.
Diversify your client base — having multiple clients simultaneously (even small ones) is a strong indicator of genuine contractor status and weakens HMRC's argument that you are economically dependent on a single client.

Frequently Asked Questions

Does IR35 apply to sole traders?+

No. IR35 applies only to workers operating through an intermediary — usually a personal service company or limited company. Sole traders who invoice clients directly are not subject to IR35. However, they may still be subject to employment status rules that determine whether they are genuinely self-employed for tax purposes — the tests are similar but the legal framework is different.

Can I work inside IR35 for one client and outside for another?+

Yes. IR35 status is determined contract by contract. You can legitimately have some contracts that are inside IR35 and others that are outside, operating through the same limited company. You must account for the income from inside-IR35 contracts as "deemed employment income" and pay tax accordingly, while income from outside-IR35 contracts can be extracted tax-efficiently as salary and dividends.

What happens if HMRC opens an IR35 investigation into me?+

For contracts before April 2021 in the private sector, liability rests with your personal service company. HMRC can open an investigation going back six years (or 20 years in cases of fraud). If they conclude you should have been inside IR35, you face a demand for unpaid income tax, NI contributions, and interest and penalties. The amounts can be substantial — an investigation covering several years can produce a six-figure liability.

What is the "small companies exemption"?+

If the end client is a small company (meeting the small companies test under the Companies Act 2006), the off-payroll rules do not apply and the responsibility for determining IR35 status remains with the contractor's own company. The small companies test requires the client to meet at least two of: fewer than 50 employees, turnover not exceeding £10.2 million, and balance sheet total not exceeding £5.1 million. If the client does not share its size information, it is treated as medium or large — so always request a formal statement of size.