IR35 Explained: A Plain English Guide for Contractors
What IR35 is, how it works, and exactly what "inside IR35" means for your take-home pay — explained clearly.
Last updated: April 2026
What is IR35?
IR35 is the common name for Chapter 8 and Chapter 10 of the Income Tax (Earnings and Pensions) Act 2003. It is tax legislation designed to ensure that contractors who work like employees — but through a personal service company (PSC) or intermediary — pay broadly the same income tax and National Insurance as permanent employees.
The legislation targets what HMRC calls "disguised employment" — where a contractor works exclusively for one client, under their direction, and is essentially indistinguishable from a permanent employee, yet pays tax at much lower rates by routing income through a limited company.
The Three Employment Status Tests
IR35 status is determined by the nature of your working arrangements, not the contract wording alone. Courts and HMRC look at three primary factors:
1. Substitution
Key Test"Can you send someone else to do the work in your place?"
Inside IR35
Client must accept you personally — no substitution allowed
Outside IR35
You have a genuine right to send a qualified substitute at your own cost
2. Mutuality of Obligation
Key Test"Is the client obliged to offer work, and are you obliged to accept it?"
Inside IR35
Client must offer work and you must accept it — like an employment relationship
Outside IR35
No obligation on either side — engagement ends when project ends
3. Control
Key Test"Who controls how, when, and where you work?"
Inside IR35
Client dictates your working hours, location, and methods
Outside IR35
You decide how to deliver the agreed outcome — you control your working methods
The 2021 Off-Payroll Working Reforms
Before April 2021, contractors working in the private sector were responsible for determining their own IR35 status. The April 2021 reforms (following similar changes to the public sector in 2017) transferred this responsibility to the end client for medium and large businesses.
Now, the end client must assess each engagement and issue a Status Determination Statement (SDS). If the determination is "inside IR35," the fee payer (usually the recruitment agency) must deduct income tax and NI at source before paying the contractor's company.
Small companies (fewer than 50 employees, under £10.2m turnover, under £5.1m balance sheet) are exempt — contractors working with small clients still self-assess their IR35 status.
Inside IR35: What Does It Mean for Your Pay?
If your contract is inside IR35, your take-home pay is calculated using standard PAYE rates — effectively the same as an employee. Working through an umbrella company is the most common and straightforward way to handle inside-IR35 contracts.
HMRC Resources
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Calculate your exact take-home on an inside IR35 umbrella contract.
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