IR35 has been part of the UK tax system since 2000. Yet in 2026, it remains one of the most commonly misunderstood areas of employment tax for tech founders and growing startups.
Getting IR35 wrong does not just create an HMRC enquiry. It can result in backdated tax, National Insurance, interest, and penalties that significantly damage a company’s finances.
This guide explains what IR35 is, how the off-payroll working rules apply to tech companies in 2026, what mistakes founders commonly make, and what to do to protect your business.
1. What Is IR35?
IR35 is a set of tax rules designed to prevent what HMRC calls disguised employment. In practice, this means preventing contractors from providing services through a limited company when, in substance, they are working as employees.
If a contractor is caught by IR35, the income they receive through their limited company is treated as employment income. This means it becomes subject to income tax and National Insurance contributions at the same rates as a regular salary.
The financial impact can be significant. A contractor earning 100,000 per year through their company who is found to be inside IR35 could face a tax and NIC bill that is tens of thousands of pounds higher than they planned for.
2. How Off-Payroll Working Rules Apply in 2026
Since April 2021, the responsibility for determining IR35 status shifted from contractors to the businesses that engage them. This is known as the off-payroll working rules.
In 2026, the rules work as follows:
- If the end client (your company) is a medium or large business, you are responsible for determining whether each contractor engagement is inside or outside IR35.
- If your company qualifies as a small company under the Companies Act 2006 definition, the responsibility for determination remains with the contractor’s personal service company.
- If you get the determination wrong as a medium or large business, your company, not the contractor, can be held liable for the unpaid tax and NIC.
Many tech startups that began as small companies have grown past the small company thresholds without realising it. This shift in size can change your legal obligations significantly.
3. How to Determine If a Contractor Is Inside or Outside IR35
HMRC uses three primary tests to assess IR35 status. No single test is conclusive. The overall picture of the working relationship matters.
Test 1: Substitution
Can the contractor send a substitute to do the work? If the contract requires the individual personally, with no right to substitute, this points toward employment. If substitution is a genuine right and has been exercised, it points toward contractor status.
Test 2: Control
How much control does your company have over how and when the work is done? If you dictate working hours, methods, and daily tasks, this looks like employment. If the contractor has genuine autonomy over how they deliver the outcome, this points toward contractor status.
Test 3: Mutuality of Obligation
Is your company obliged to offer work and is the contractor obliged to accept it? A continuous flow of work with an expectation of ongoing engagement points toward employment. A defined project with a clear start and end, and no obligation to offer further work, points toward contractor status.
HMRC also provides a free tool called CEST (Check Employment Status for Tax) which gives an indicative determination. However, CEST is not definitive, and HMRC has been known to challenge determinations that relied solely on the tool without proper contract and working practice review.
4. Common Mistakes UK Tech Founders Make
- Assuming small company status without checking: The small company thresholds under the Companies Act 2006 are turnover below 10.2 million, balance sheet below 5.1 million, and fewer than 50 employees. If you have crossed two of these three thresholds in two consecutive years, you are no longer small. Many fast-growing tech startups pass this point quietly.
- Using the same contract for every contractor: A generic contract that has not been reviewed by a tax specialist is not a defence against an HMRC enquiry. Contracts must reflect the actual working relationship, not just what both parties would prefer the relationship to look like on paper.
- Completing a Status Determination Statement but not delivering it: When a medium or large company determines a contractor is inside or outside IR35, they are legally required to issue a Status Determination Statement (SDS) to the contractor and any agency in the supply chain. Not issuing the SDS means the liability stays with the client company regardless of the determination.
- Ignoring working practices: A contract can say the contractor has the right to substitute. But if no substitution has ever occurred and the contractor attends stand-ups every day and uses company equipment, HMRC will look at the actual working relationship, not just what the contract says.
- No appeals process in place: If you make a determination that a contractor disagrees with, they have the right to challenge it. Medium and large companies must have a written disagreement process. If you do not have one, this is a compliance failure in itself.
5. What a Good IR35 Process Looks Like
For tech companies engaging contractors in 2026, a proper IR35 process includes:
- A contract review by a qualified specialist for each new contractor engagement
- A genuine assessment of working practices, not just contract terms
- A completed Status Determination Statement issued to the contractor before work begins
- A written disagreement process available to contractors
- A review process triggered by any material change in working practices
- Clear internal records of all determinations and the reasoning behind them
This does not need to be complex. For most tech startups, a consistent and documented process is enough to demonstrate reasonable care to HMRC if a question is ever raised.
6. IR35 and HMRC Enquiries: What to Expect
HMRC has significantly increased its focus on off-payroll working compliance since 2021. Enquiries can be triggered by payroll data, contractor self-assessment filings, or sector-wide reviews targeting industries with high contractor use, including technology.
If HMRC opens an enquiry into your IR35 compliance, they will typically request contracts, working practice evidence, and Status Determination Statements. Having these ready significantly reduces the time and cost of responding.
If HMRC finds that determinations were incorrect and the company failed to take reasonable care, penalties can be charged on top of any backdated tax and NIC.
Final Thoughts
IR35 is not going away. HMRC has made off-payroll compliance a long-term enforcement priority, and the technology sector remains one of the highest-risk industries for contractor misclassification.
The good news is that compliance is achievable. A clear process, properly reviewed contracts, and accurate Status Determination Statements are enough to protect most UK tech companies from exposure.
The time to build that process is before HMRC asks the question.
Not Sure About Your IR35 Position?
Book a free consultation with our UK tax and employment specialists at SustainEdge Global.
We will review your contractor arrangements, assess your IR35 exposure, and help you build a compliant process that protects your business.
Book your free consultation today: https://sustainedgeglobal.com/uk/contact-us/
