IR35 Explained: A Practical Guide for UK Startups Hiring Contractors

If you’re a startup founder hiring contractors to move fast (without taking on permanent headcount), you’re not alone.

But as soon as you start paying individuals through their limited companies, the IR35 rules can quickly become the “wait… are we doing this right?” moment.

This guide breaks down IR35 in plain English from a small business perspective, so you can hire contractors confidently, reduce tax and employment-law risk, and set up sensible processes from day one.

We’ll keep this practical and plain-English. No legal waffle. (And just a quick note: this article is general information only and isn’t tax or financial advice - IR35 can be fact-specific, so you may also want advice from an accountant or tax specialist.)

What Is IR35 (Explained Simply) And Why Should Startups Care?

IR35 is the common name for the UK’s “off-payroll working” rules. In simple terms, these rules are designed to stop “disguised employment”.

Disguised employment is where someone works like an employee, but is paid like a contractor-often through their own limited company (sometimes called a personal service company or “PSC”).

From a startup’s perspective, IR35 matters because:

• Tax risk can land with your business (depending on your size and the payment chain).
• IR35 often overlaps with employment-law risk (for example, if the working arrangement looks like employment, you may also face worker/employee claims).
• It affects contractor costs (inside IR35 roles can be more expensive because of tax treatment and expectations around rates).
• It affects how you structure the relationship-your contract and your day-to-day working practices need to match.

IR35 is not “just paperwork”. It’s really about whether the relationship is genuinely independent contracting, or essentially employment in practice.

When Does IR35 Apply When You Hire A Contractor?

IR35 generally comes into play when all of the following are true:

• You engage an individual to provide services to your business;
• That individual supplies the services via an intermediary (most commonly their own limited company); and
• If you removed the intermediary, the individual would look like an employee of your business (based on how they work day-to-day).

If you’re paying someone as a sole trader (in their own name), IR35 usually isn’t the same issue. But you still need to think about employment status and misclassification risk.

Common Startup Scenarios Where IR35 Comes Up

• Long-term “contractor” who works 4–5 days a week for you, uses your systems, attends team meetings, and has a company email address.
• Product and engineering contractors who are embedded in squads and managed like employees.
• Fractional roles (CTO, CMO, CFO) where the person is senior, integrated, and subject to significant control.
• “Temp-to-perm” arrangements where someone starts as a contractor but is treated like an employee from day one.

None of these are automatically “inside IR35”, but they’re high-risk if the structure and reality aren’t thought through.

Who Is Responsible For IR35 Compliance (And Does The Small Company Exemption Apply)?

This is the part that trips up a lot of founders, because the answer depends on whether your business is “small” for IR35 purposes-and also on how the contractor is engaged and paid.

If Your Startup Is A Small Company

If you qualify as a small company for off-payroll working, the responsibility for IR35 status (and the tax) will often stay with the contractor’s intermediary (e.g. their PSC). In other words, the contractor typically assesses whether IR35 applies and accounts for the right tax.

However, “small company” is a defined legal test (and can be nuanced in group structures or where linked/partnered businesses are involved). It can also change as you grow. If you scale quickly, you can move out of “small” and into the off-payroll regime where the burden shifts to you.

If Your Startup Is Medium Or Large

If you’re medium or large, your business (as the client) generally needs to:

• Make a status determination (inside or outside IR35);
• Provide a written Status Determination Statement (SDS) and pass it down the chain; and
• Have a process to deal with disagreements about the determination.

Depending on the payment chain (for example, if there’s an agency involved), the “fee-payer” (often the party paying the PSC) may have to operate PAYE and National Insurance for inside IR35 engagements. Getting the chain wrong can create liability and dispute risk, so it’s worth being clear up front on who is contracting with whom and who is paying whom.

Even If You’re Small, You Still Need To Manage The Risk

Startups often assume “we’re small, so IR35 isn’t our problem”. But in practice, you still want to manage:

• Commercial risk (contractors changing rates or walking away if a role is deemed inside IR35);
• Employment status risk (a contractor claiming they were really an employee or worker); and
• Investor and due diligence risk (IR35 and contractor classification can come up in funding rounds or acquisitions).

Getting your contracts right early is a big part of this. For many startups, that starts with a properly structured Contractor Agreement that matches how you actually plan to work together.

IR35 Status Explained Simply: The Key Tests HMRC Looks At

There isn’t one single magic factor. In practice, IR35 status is assessed using a bundle of indicators that point towards either:

• Employment-like (higher risk of “inside IR35”), or
• Genuine independent contracting (more likely “outside IR35”).

Here are the big ones, explained simply.

1) Control: Who Decides How The Work Is Done?

The more your startup controls how, when, and where the contractor works, the more the relationship can resemble employment.

Lower-risk indicators (more “contractor-like”):

• The contractor decides their own working pattern (within reason).
• You specify outcomes/deliverables rather than day-to-day instructions.
• The contractor uses their own methods and professional judgement.

Higher-risk indicators (more “employee-like”):

• You set fixed working hours and require attendance like staff.
• The contractor is managed like an employee with performance reviews.
• The contractor must ask permission for time off.

2) Substitution: Can They Send Someone Else?

A genuine “right of substitution” (where the contractor can send a suitably qualified replacement) can point away from employment.

But it needs to be real. If your contract says substitution is allowed, but in reality you’d never accept it (or the role is inherently “person-specific”), that weakens the position.

3) Mutuality Of Obligation: Is There Ongoing Obligation On Both Sides?

This is often described as:

• Are you obliged to offer work continuously?
• Is the contractor obliged to accept it?

Project-based engagements with clear start/end points, milestones, and the ability to decline additional work tend to look more contractor-like.

4) Financial Risk And “In Business On Their Own Account”

Contractors are usually running a business. Employees usually aren’t.

Things that can support an “outside IR35” position include:

• The contractor provides their own equipment (where sensible for the role).
• The contractor can make a profit or loss (e.g. fixed price project, correcting defects in their own time).
• The contractor markets their services to multiple clients.

5) Integration: Do They Look Like Part Of Your Team?

If the contractor is fully embedded (company email, org chart, managing employees, representing the business externally as “one of you”), that can increase risk.

This is where startups need to be especially careful-because early teams are naturally tight-knit. You can still build a great working relationship, but you want to avoid creating an arrangement that is employee-like in substance.

A Practical IR35 Checklist For Startups Hiring Contractors

Once you understand the principles, the next step is setting up a repeatable process that founders and hiring managers can actually follow.

Here’s a practical checklist you can use each time you engage a contractor.

Step 1: Decide The Engagement Model Upfront

Before you talk rates, get clear on what you’re buying:

• A deliverable/project (e.g. “build feature X by date Y”), or
• Extra capacity in the team (e.g. “a developer to join the squad and pick up tickets”).

Project/deliverable-based engagements are often easier to structure as genuinely independent. Capacity-based engagements can still be legitimate contracting, but you’ll need to be much more careful about control and integration.

Step 2: Put The Right Contract In Place (And Match It In Real Life)

Your written agreement matters, but HMRC (and courts/tribunals, if things escalate into status disputes) will also look at what happens day-to-day.

Depending on the scenario, you might use:

• A Consulting Agreement for advisory/fractional support;
• A Freelancer Agreement for independent creative/marketing/ops services;
• A Contractor Agreement consult where the arrangement is high-value, long-term, or complex.

Key clauses you’ll usually want to think about include:

• Scope and deliverables (what “done” looks like);
• Payment structure (daily rate vs milestone);
• Substitution (if appropriate, and workable in practice);
• IP ownership (so your startup owns the outputs you’re paying for);
• Confidentiality (especially if they’ll see product roadmaps, code, customer data);
• Termination (including short notice if you need flexibility);
• Status wording (confirming independent contractor relationship-while being careful not to rely on labels alone).

If you need help tailoring those provisions to your actual risk profile, a Clause Drafting service can be a practical way to tighten up the areas that matter most for your business model.

Step 3: Avoid “Employee-Like” Working Practices By Default

Even with a solid contract, your processes can accidentally create IR35 and employment-status risk. Common examples include:

• Giving contractors the same benefits/perks as employees (beyond basic access needed for the work).
• Requiring contractors to follow staff policies that don’t apply (or aren’t adapted).
• Managing contractors with the same performance management framework you use for employees.

This doesn’t mean contractors can’t attend meetings or collaborate. It means you should keep the focus on deliverables and outcomes, not “line management”.

Step 4: Get Clear On Data And Systems Access

Startups often need contractors to work inside internal tools (repos, ticketing, CRM, analytics). That’s normal-but it needs to be done safely.

If contractors will access personal data (customer lists, user analytics, marketing databases, HR info), you may also need to think about GDPR compliance and whether a data processing arrangement is required. For businesses building out their compliance foundations, a GDPR package can help set up the right policies and contractual protections.

Step 5: Know When You Should Hire An Employee Instead

Sometimes the “contractor route” feels faster, but it can be the wrong fit. Consider an employment relationship where:

• You need someone full-time and ongoing, indefinitely;
• You need tight control over hours, location, and methods;
• The person will be deeply integrated into management and decision-making; or
• The role is part of your core business operations (not a defined project).

In those cases, using an Employment Contract can be the cleaner way to reduce uncertainty and build a stable team-especially if you’re scaling.

Common IR35 Mistakes Startups Make (And How To Avoid Them)

Founders are busy. Contractors are moving quickly. That’s exactly when mistakes happen.

Here are some of the most common IR35-related pitfalls we see in small businesses-and what to do instead.

Mistake 1: Treating IR35 As A “Finance Problem” Only

IR35 is tax-focused, but the underlying question is about the nature of the working relationship. If the relationship looks like employment, that can have knock-on effects beyond tax (including employment status disputes).

What to do instead: Align finance, legal, and hiring decisions. Your contract, onboarding, and day-to-day management should all point in the same direction.

Mistake 2: Using A Generic Template That Doesn’t Match Reality

If your contract says “no control” and “right of substitution”, but your team treats the contractor like a permanent employee, the contract won’t save you.

What to do instead: Use a contract that reflects how you’ll actually operate, and train managers on the “dos and don’ts” for contractor engagements.

Mistake 3: Rolling Renewals Forever

Extending a contractor for months (or years) without revisiting status and working practices can build risk over time-especially as your startup grows and your “small company” position changes.

What to do instead: Build a simple review point into your process (e.g. every 3–6 months): scope, deliverables, integration level, and whether the role has evolved into an employee-shaped need.

Mistake 4: Forgetting About IP Ownership

From a startup perspective, one of the biggest practical risks of contractor hiring isn’t just IR35-it’s paying for work and then not clearly owning it.

What to do instead: Ensure your contractor documentation properly assigns IP and addresses confidentiality. This is particularly important for code, designs, branding, and content.

Key Takeaways

• IR35 explained simply: it’s about whether someone is really working like an employee, even though they’re paid through an intermediary like their limited company.
• Your IR35 responsibilities depend on your size-the “small company” position can reduce obligations, but you still need to manage commercial and employment-status risk.
• Status is driven by reality, not labels: control, substitution, mutuality of obligation, financial risk, and integration are key indicators.
• Strong contracts help-but only if working practices match, so align hiring, management, and onboarding with the engagement model.
• Use the right legal document for the relationship (contractor/freelancer/consulting) and make sure IP, confidentiality, and termination are properly covered.
• Sometimes the best risk-reduction move is to hire as an employee if the role is truly ongoing, full-time, and tightly controlled.

If you’d like help setting up contractor arrangements or getting the right contracts in place for your startup, you can reach us at 08081347754 or team@sprintlaw.co.uk for a free, no-obligations chat.