IR35 and Invoicing: What Freelancers Need to Know

What Is IR35 and Why Does It Matter for Invoicing?

IR35 — formally known as the off-payroll working rules — is HMRC legislation designed to prevent "disguised employment." The idea is straightforward: if you work for a client and the arrangement looks like employment (a single client, working defined hours, little financial risk), HMRC believes you should pay employment taxes, not lower self-employed rates.

Getting IR35 wrong can result in substantial back-tax bills. Getting it right means you can continue invoicing as a legitimate self-employed professional.

Who Does IR35 Apply To?

IR35 applies to contractors who provide services through a personal service company (PSC) or similar intermediary. It does not directly apply to sole traders who invoice clients directly — though HMRC may still scrutinise arrangements that look like disguised employment.

The rules changed significantly in 2021. For medium and large private-sector clients (and all public sector clients), the client is now responsible for determining your IR35 status, not you. They issue a Status Determination Statement (SDS) declaring whether your engagement falls inside or outside IR35.

For small private-sector clients (fewer than 50 employees and annual turnover under £10.2m), you are still responsible for your own IR35 determination.

The Key Tests: Are You Inside or Outside IR35?

HMRC uses several factors to determine status:

Substitution: Can you send a substitute to do the work instead of yourself? Genuine contractors can; employees cannot. If your contract includes a meaningful right of substitution, this points toward outside IR35.

Control: Does the client control how, when, and where you work? Employment-level control indicates inside IR35. Contractors are typically told what to deliver, not how to do it.

Mutuality of obligation: Is the client obliged to offer you work and are you obliged to accept it? An ongoing expectation of work on both sides looks like employment.

Part and parcel of the organisation: Are you treated like an employee? Attending internal meetings, having a company email address, and appearing on org charts all point toward inside IR35.

Financial risk: Do you bear financial risk — fixed-price contracts, your own equipment, the possibility of having to redo work at your own cost? Genuine contractors have financial risk.

How IR35 Affects Your Invoicing

If you are outside IR35: You invoice normally. You are genuinely self-employed, pay your own tax via self assessment, and can claim business expenses.

If you are inside IR35: The fee you invoice is treated as employment income. The client (or the agency) must deduct income tax and National Insurance before paying you, similar to payroll. You pay employer's NI on top. Your take-home is considerably lower.

Inside IR35 also affects what you can claim as expenses. The "deemed salary" calculation limits deductions to a 5% allowance for business costs (previously available to PSC contractors), which has now been removed for most inside-IR35 arrangements.

Protecting Your Outside-IR35 Status

If your work genuinely falls outside IR35, protect that status through:

• A robust contract: Ensure substitution, limited control, and financial risk are clearly drafted. Consider a contract review from a specialist IR35 consultant.
• Working practices match the contract: A contract saying you can substitute is undermined if you never could in practice.
• Multiple clients: Working for several clients simultaneously is strong evidence of genuine self-employment.
• Your own equipment and insurance: Using your own tools and carrying professional indemnity insurance reinforces contractor status.
• Clear project deliverables: Being engaged for a specific outcome (a website, a report, a design system) rather than being available as a resource looks more like self-employment.

Invoicing as a Sole Trader vs. PSC

Most freelancers invoicing as sole traders face a simpler version of IR35 — HMRC cannot use the IR35 rules directly against sole traders, but they can investigate arrangements that look like disguised employment and reclassify them.

The practical protection is the same: genuine self-employment characteristics, multiple clients, clear project-based work, and your own working practices.

For managing invoices, payment reminders, and keeping a clear record of your client work, tools like InvoicePulse make it easy to demonstrate you are running a professional self-employed business — multiple clients, systematic billing, and clear records.