IR35, also known as the off-payroll working rules, ensures contractors pay broadly the same tax and National Insurance as employees when their working arrangement mirrors employment. If you would have been an employee without your limited company, IR35 applies.
In this guide we’ll explain how IR35 works, who decides your status, and how to reduce risk.
Table of Contents
What Is IR35?
IR35 is UK tax legislation introduced to prevent disguised employment. It applies when a worker supplies services through an intermediary, usually a limited company, but works in the same way as an employee. HMRC looks beyond job titles and focuses on how the work is actually carried out. This is why contractors often seek advice from experienced professionals rather than relying on assumptions or online tools alone.
If you are unsure whether your setup qualifies as genuine self-employment, reviewing it alongside a qualified tax advisor is essential.
Why IR35 Was Introduced
Before IR35, many contractors reduced tax by:
- Taking dividends instead of salary
- Paying lower National Insurance
- Working long-term for one client
HMRC introduced IR35 to create fairness between permanent employees and contractors doing identical work. Today, this affects thousands of contractors across IT, construction, finance, and consultancy.
Who the Off-Payroll Rules Apply To
You may be affected if you are:
- A contractor working through a limited company (PSC)
- A business engaging contractors via intermediaries
- An agency supplying contractors to end clients
IR35 does not apply to sole traders, which is why many self-employed individuals fall under different tax considerations.
When IR35 Applies (Public, Private & Small Clients)
The responsibility for deciding IR35 depends on the client’s size.
- Public sector: client decides (since 2017)
- Medium or large private-sector businesses: client decides (since April 2021)
- Small private-sector businesses: contractor decides
This distinction is critical and often misunderstood. Many contractors wrongly assume the client always decides, which is not true when working with small companies. If you are unsure whether your client qualifies as “small”, professional guidance can prevent costly mistakes.
Inside IR35 vs Outside IR35 (Key Differences)
| Feature | Inside IR35 | Outside IR35 |
|---|---|---|
| Tax method | PAYE | Corporation tax |
| NIC | Employee & employer | None |
| Take-home pay | Lower | Higher |
| Business risk | Minimal | Genuine |
Being inside IR35 can reduce take-home pay by 20–30%, depending on income level.
How IR35 Status Is Determined
HMRC reviews two things:
The Contract
Contracts are checked for clauses on:
- Control
- Substitution
- Mutuality of obligation
Poorly drafted contracts are a common issue, especially when templates are reused across roles.
Actual Working Practices
Even a “perfect” contract fails if reality does not match it.
Examples HMRC looks at:
- Who controls your work?
- Can you refuse tasks?
- Can you send a substitute?
- Do you correct mistakes at your own cost?
What Is a Status Determination Statement (SDS)?
An SDS explains whether IR35 applies and why. Medium and large clients must:
- Issue the SDS in writing
- Share it with the contractor and agency
- Offer a dispute process
Without a valid SDS, tax liability can shift back to the client.
Using the CEST Tool (And Its Limits)
HMRC provides the Check Employment Status for Tax (CEST) tool, but it has limitations and relies heavily on how questions are answered. CEST does not account well for complex or hybrid roles, which is why disputes still arise.
Working Through an Umbrella Company
If you are employed by an umbrella company:
- PAYE already applies
- IR35 usually does not apply directly
However, umbrella arrangements often come with:
- Higher deductions
- Reduced flexibility
Before switching, compare this with limited company contracting.
How IR35 Works
Inside IR35:
A contractor works fixed hours, reports to a manager, uses company equipment, and cannot send a substitute.
Outside IR35:
A contractor delivers project-based work, invoices monthly, uses their own tools, and retains autonomy.
These differences are small on paper but decisive in HMRC enquiries.
What Happens If IR35 Is Applied Incorrectly?
Incorrect IR35 decisions can result in:
- Backdated Income Tax
- National Insurance arrears
- Interest and penalties
Contractors often face these issues years later during compliance checks, similar to late-identified tax errors.
How Path Accountants Help With IR35
We support contractors and businesses with:
- IR35 contract reviews
- Working practice assessments
- SDS dispute support
- HMRC enquiry assistance
The goal is clarity, compliance, and reduced risk.
Conclusion
IR35 is about how you work, not what you call yourself. Understanding your status before signing a contract protects your income, avoids disputes, and ensures long-term compliance. If you work with UK clients regularly, IR35 should be reviewed as carefully as pricing or contract length.
FAQs
How do I know if I’m inside or outside IR35?
You are inside IR35 if your role looks like employment in practice for example, you work set hours, take instructions like staff, and cannot send a substitute. You are outside IR35 if you operate independently, control how work is done, and take genuine business risk.
The contract matters, but HMRC focuses more on what actually happens day to day.
Can I be outside IR35 with only one client?
Yes, having one client does not automatically put you inside IR35. What matters is how you work. Many contractors have a single long-term client but remain outside IR35 because they control their work, invoice monthly, and operate as a genuine business.
Does IR35 apply if I work from home?
Working from home does not affect IR35 status on its own. HMRC cares about control, substitution, and mutual obligations not your location. Remote contractors can be inside or outside IR35 depending on how the engagement is structured.
What happens if my client gets IR35 wrong?
If a medium or large client issues an incorrect Status Determination Statement (SDS), they can become liable for unpaid tax and National Insurance. Contractors can challenge the decision, and clients must respond with reasons. Incorrect decisions often lead to disputes and delayed payments.
Does IR35 apply to fixed-price or project work?
Fixed-price and project-based contracts are more likely to be outside IR35, especially when payment depends on delivery rather than time worked. However, poor working practices can still pull a project inside IR35.
What’s the biggest mistake contractors make with IR35?
The most common mistake is assuming they are outside IR35 without checking. Many contractors only review IR35 after an HMRC enquiry starts when it is already too late to fix contracts or working practices.
