IR35 Rules Explained for Businesses in 2026

Updated with the latest legal and practical insights as of 2026

IR35 legislation, also known as the intermediaries legislation, has undergone significant reform in recent years. For businesses engaging contractors, understanding the off payroll working rules is now a core compliance requirement.

This comprehensive guide to IR35 explains in simple terms what IR35 means, when IR35 applies, who is responsible for issuing IR35 status in 2026, and what the rules mean for contractors and businesses alike.

If your organisation works with limited company contractors, personal service companies, or contractors and freelancers, this guide will help you understand your responsibilities under UK tax legislation.

What Is IR35?

The term IR35 refers to UK tax legislation introduced over two decades ago to prevent tax avoidance through intermediaries, typically limited companies or personal service companies.

IR35 targets situations where a contractor working through a limited company would be regarded as an employee for tax purposes if that intermediary did not exist.

In simple terms, if a contractor looks and operates like an employee, HMRC may treat them as an employee for tax purposes, even if they invoice through their own company.

IR35 rules apply to both the private sector and the public sector, but responsibility for determining IR35 status depends on the size and type of the end client.

Why IR35 Matters to Businesses and Contractors

From a business perspective, IR35 is about risk management.

If IR35 applies and the engagement is deemed inside IR35, PAYE income tax and National Insurance contributions must be deducted. Employer National Insurance contributions may also be payable.

If handled incorrectly, HMRC may transfer tax liabilities to the business.

For contractors, working inside IR35 means reduced take home pay and operating under tax rules similar to employment.

Understanding whether IR35 applies protects both contractors and businesses.

How IR35 Has Changed

IR35 has undergone major reform in recent years.

Since April 2021, medium and large private sector organisations have been responsible for implementing  a contractor’s IR35 status. This aligned the private sector with earlier public sector reform.

From April 2026, updated small business thresholds will again shift responsibility for determining IR35 status in certain cases which is following alongside the Employment rights act.

Understanding these changes to IR35 is critical for compliance.

What Is a Status Determination Statement

A Status Determination Statement (SDS) is a formal document confirming the IR35 status determination for a contractor.

If you are responsible for determining IR35 status, you must:

• Conduct an IR35 assessment
• Provide a written SDS
• Explain your reasoning
• Offer a disagreement process
• Take reasonable care

Failure to take reasonable care can shift tax liabilities to the end client.

How HMRC Assesses IR35 Status

HMRC doesn’t use a single formula but instead it looks at the real working relationship between the contractor and client.

The tests are built around common law status factors:

1.Supervision, Direction & Control (SDC)

SDC looks at how much control the client has over the contractor’s work:

• Supervision:Are you being overseen in how you do your work?
  Example: A manager constantly checks your progress or tells you exactly how to do each task.
• Direction:Are you being told what work to do and when?
  Example: You are given strict instructions to complete tasks in a set order or timeline.
• Control:Are you being controlled in the way you perform your work?
  Example: You have to use certain methods, tools, or follow exact processes dictated by the client.

The more SDC exists, the more likely HMRC will see you as effectively an employee, which could put you inside IR35.

How HMRC Applies This

HMRC asks questions like:

• Do you decide how and when to do the work, or is it dictated by the client?
• Can you delegate the work to someone else if you choose?
• Are you required to work on-site under supervision, or can you work independently?
• Are there detailed rules you must follow, or just objectives to achieve?

Key principle: Independent contractors should have freedom over how the work is done, even if the client sets deadlines or outcomes.

2. Substitution

One of the strongest indicators to HMRC that you’re genuinely operating as a contractor is the right to provide a substitute, the ability to send someone else to do the work if you’re unavailable.

A genuine contractual right of substitution strongly supports an outside IR35 status. Conversely, if your contract either doesn’t allow a substitute or lets the client unreasonably refuse one, it points toward an employee-like arrangement.

Many contracts include a substitution clause requiring the client to confirm they’re happy for a substitute to step in when needed. However, simply having this clause isn’t enough on its own. HMRC will expect it to be practically feasible: could someone else realistically take over your tasks, and how would that work in practice?

Evidence that a substitute has actually been used during the contract is a strong sign of self-employment. When a substitute is used, it’s typically at your cost, and you remain responsible for training them and making the necessary arrangements.

The client also has the right to reasonably veto a substitute if they’re unqualified or unsuitable for the role, and this does not undermine your outside IR35 position.

While substitution clauses and practices are powerful indicators of self-employment, not having them does not automatically mean you fall inside IR35. HMRC considers a range of other factors when assessing status.

3. Mutuality of Obligation (MOO)

A contract of service requires an ‘irreducible minimum of mutual obligation’. This means that the client is obliged to remunerate the contractor, and the contractor is obliged to provide their services.

A self-employed person would expect to be hired to undertake a task, with no expectation of further work once the contract is completed.

A genuine contract for services normally lacks continuous mutual obligations, whereas employment has them.

Recent cases suggest MOO alone no longer carries as much defensive weight unless the whole relationship shows true independence.

If, once a contract is completed, another is offered, this may raise questions. If your contract is renewed multiple times, this could be viewed as bypassing a contract of employment. In HMRC’s words, “where work is regularly offered and accepted over a period of time a continuous contract of employment may be created.”

Other Factors That Matter

In addition to the “holy trinity” above, HMRC will consider several nuance factors:

✔ Financial risk – Do you bear risk of loss?
✔ Provision of equipment – Do you use your own tools?
✔ Part and parcel – Are you part of the organisational hierarchy?
✔ Business On Own Account – Are you trading as a real business?

These aren’t standalone tests, but they help build a holistic picture.

Inside or Outside IR35 What It Means

Understanding inside or outside IR35 is essential.

Inside IR35

• The contractor is treated as an employee for tax purposes
• Income tax and National Insurance contributions are deducted
• Employer National Insurance contributions may apply
• The engagement follows off payroll working rules

Contractors inside IR35 are taxed similarly to employees, even if operating through limited companies.

Outside IR35

• The contractor is genuinely self employed
• They operate as a business to business supplier
• They manage their own IR35 tax affairs
• The outside IR35 rules allow greater tax efficiency

Whether you are inside or outside IR35 significantly affects cost models and contractor engagement strategy.

IR35 Compliance checklist

An organised compliance approach keeps contractors safe during HMRC investigations and status determinations. Use the following checklist to confirm your IR35 position and maintain strong documentation

For Outside IR35 contractors

• Have a written contract that includes a genuine substitution clause
• With clear project deliverables and end dates
• Demonstrate control over how, when, and where you work
• Use your own equipment and take on financial responsibility where appropriate
• Maintain professional business insurance, such as PI or PL
• Operate as a legitimate business, with a website and marketing materials to reflect your status
• Work with multiple clients where possible to show business independence
• Invoice for deliverables or milestones, rather than simply hours worked
• Take on financial risk for mistakes, delays, or rework
• Keep detailed records of contracts, correspondence, and actual working arrangements
• Document your IR35 assessment and reasoning, particularly if you self-assess from April 2026

For Inside IR35 contractors:

• Familiarise yourself with your Status Determination Statement (SDS) and the reasoning behind it
• Check who is responsible for PAYE deductions whether that be client, agency, or umbrella company
• Evaluate umbrella company options if you must work through one
• Use a reliable inside IR35 calculator to estimate your actual take-home pay
• Assess whether the contract terms and fee make it worthwhile to continue under inside IR35 rules
• Ensure payslips clearly show Income Tax and National Insurance deductions
• Keep detailed records of all payments, taxes deducted, and any expense claims
• File a Self-Assessment or personal tax return if needed for additional income or reconciliation
• Consider your client’s size to understand if you’ll be responsible for self-assessing from April 2026

Who Is Responsible for Determining IR35 Status from April 2026

From April 2026, the rules around IR35 compliance are changing, and responsibility for determining a contractor’s status will depend on the size of the end client.

Public Sector

All public sector organisations remain responsible for determining IR35 status and issuing a Status Determination Statement (SDS). They must ensure that engagements comply with the rules.

Private Sector

In the private sector, responsibility depends on the size of the business:

• Small businesses: Contractors will now self-assess their IR35 status and maintain detailed records showing how their work is carried out. Small companies themselves are not responsible for determining status.
• Medium and large businesses: The client remains responsible for assessing IR35 status and issuing an SDS.

A business qualifies as small if it meets two or more of the following criteria:

1. Turnover of £15 million or less
2. Balance sheet total of £7.5 million or less
3. 50 employees or fewer

If a business exceeds two of these thresholds, it will continue to be responsible for determining IR35 status for contractors it engages.

New Small Company Thresholds (from 6 April 2026)

From 6 April 2026, the criteria for what counts as a small company in the UK will change. A company will be considered small if it meets at least two of the following:

• Annual turnover:£15 million or less (up from £10.2 million)
• Balance sheet total:£7.5 million or less (up from £5.1 million)
• Number of employees:50 or fewer (unchanged)

These thresholds affect who is responsible for determining IR35 status:

And broken down by client type:

Contractors working with businesses that are newly reclassified as small companies will need to self-assess their IR35 status from April 2026, while medium and large organisations, and all public sector bodies, will continue to handle assessments and issue Status Determination Statements (SDS).

Industry-specific considerations

As we specialise in the IT and Tech space we wanted to highlight how IR35 affects the sector.

IT and Technology contractors

Tech contractors often face unique challenges due to project-based work and remote working arrangements. Clear documentation of project scope, deliverables and working practices is essential. Many IT roles naturally suit outside IR35 status due to specialist skills, autonomy and the project-based nature of engagements.

What Happens if You Get It Wrong?

It’s not clear who “you” is when referring to who pays the tax bill. It is the recruitment business or the end client, not the contractor. This puts even more empathises on the end client to get it right because it might come back to bite them, especially is the end client didn’t take reasonable care in undertaking the Status Determination Statement.

If HMRC deems you inside IR35 on review:

• You may owe unpaid tax and NICs.
• Penalties/interest can apply.

Because of these risks, many contractors consult specialists and IR35 insurance providers.

Supply Chain Liability and Umbrella Companies

In addition to IR35 compliance, contractors and businesses should also be aware of Joint and Several Liability (JSL) rules affecting umbrella company arrangements, which are expected from April 2026.

These rules strengthen HMRC’s ability to recover unpaid tax if an umbrella company fails to correctly operate PAYE or National Insurance contributions. Previously, the umbrella company itself was generally the main party responsible for payroll compliance. Under the new framework, however, HMRC may pursue other parties in the supply chain, including recruitment agencies and, in some cases, the end client receiving the contractor’s services.

For contractors working inside IR35 through an umbrella company, this change highlights the importance of knowing how your pay is processed and ensuring your umbrella provider is fully compliant. For businesses and agencies, it emphasises the need to:

• Conduct thorough checks on umbrella companies before engagement

• Ensure payroll arrangements are transparent and PAYE/NIC compliant

• Review contracts and indemnities with recruitment partners or intermediaries

While JSL rules do not change IR35 status itself, they form part of the broader regulatory landscape governing contractor engagements. Understanding these responsibilities helps both contractors and businesses avoid unexpected tax liabilities and strengthens confidence in the supply chain.

Best practices for 2026 Relating To The Changes to IR35

Navigating IR35 successfully requires proactive planning, thorough documentation and regular updates. Implementing these best practices helps contractors stay compliant, manage risks and maximise financial returns.

Prepare for April 2026 responsibility shift

• Check if your current client qualifies as small under the new April 2025 thresholds
• If yes, conduct a professional IR35 assessment before April 2026 to understand your position
• Update contracts and working practices now to ensure they align with your intended status
• Consider professional IR35 insurance if you’ll be responsible for own determination from April 2026
• Build comprehensive documentation to support your status determination

Regular status reviews

• Review your IR35 status whenever circumstances change significantly.
• This includes new contracts, changed working arrangements or updated legislation.
• Annual reviews are good practice even without changes – regular assessment helps identify potential compliance issues early.
• With the April 2026 changes, conduct a specific review of any clients who may be reclassified as small.

Professional advice

• Consult accountants, tax advisors or IR35 specialists for complex situations.
• Professional advice helps ensure compliance and optimises your contracting arrangements.
• Many contractors use specialist services for contract and working practice reviews, as well as formal status determinations

Documentation and evidence

Maintain thorough records of all contracts, correspondence, client communications and actual working practices. Well-organised evidence supporting your IR35 status determination proves invaluable during HMRC investigations or disputes. Consistent documentation demonstrates your genuine business operations and ongoing compliance.

Stay informed

As of early 202, IR35 legislation remains a significant factor for contractors and clients alike. Improved assessment processes and recent legal developments provide clearer guidance on key IR35 aspects. Staying informed of changes helps contractors adapt their working practices and contracts, maintaining compliance and minimising risk.

How Mexa Solutions Supports Contractors

At  Mexa Solutions, we understand the complexities of contracting and are here to support you every step of the way. Whether you’re a seasoned contractor or considering making the leap, we offer a wide range of services to ensure you’re successful:

• IR35 Guidance: We help contractors understand the intricacies of IR35 and ensure their contracts are compliant, giving you peace of mind that you’re working under the right terms.
• Limited or Umbrella Setup Advice: We can guide you through setting up as a limited company contractor or choosing an umbrella company based on your individual needs and future goals.
• Rate Negotiation: We make sure you’re paid what you’re worth by handling rate negotiations, ensuring you receive fair compensation for your skills and experience.
• CV Review: Contracting often means working in multiple roles. We help you streamline your CV to showcase the most relevant experience and achievements, avoiding unnecessary length and repetition. You can find more tips on how to thrive as a contractor in our latest blog.
• Hassle-Free Payroll: With our partnership with an industry-leading finance provider, you can get paid within just three days of timesheet approval. No more chasing payments – just a simple, efficient payroll process.

Final Thoughts

IR35 remains one of the most important considerations for UK contractors. Understanding how the tests apply in practice and updating both contracts and working practices reduces risk and improves your financial outcomes.

As with any tax rule, professional advice tailored to your circumstances is strongly recommended.

Further Reading / Resources

• Understanding off-payroll working (IR35) – HMRC

Our summary above is just that, and isn’t intended to be used as advice. Please refer to the above resources and do your own research!

FAQ’S

What does it mean to be inside IR35?

Inside IR35 is something the HMRC treats you as an employee for tax purposes, requiring PAYE tax and National Insurance deductions from your earnings.

What does it mean to be outside IR35?

Outside IR35 means you’re a genuine business owner, paying tax through your company via salary and dividends, retaining tax efficiency.

How often should IR35 status be reviewed?

Review IR35 status with each new contract, significant changes in working arrangements or annually as best practice. From 2026, also review if your client’s company size changes or may be reclassified as small.

What happens from April 2026 with the company size changes?

From April 2026, contractors working with newly reclassified small companies (under the new April 2025 thresholds) will take responsibility for their own IR35 determinations, ending the client’s responsibility. Contractors must prepare now by conducting professional assessments and maintaining robust documentation.

This blog was written by Bob Bath, Director and Founder of Mexa Solutions.