IR35 Explained 2026/27: Inside vs Outside, Risk, and Protecting Yourself

IR35 Explained 2026/27

IR35 is HMRC's framework for identifying contractors who work like employees but use limited companies to reduce their tax and NI burden. Named after the 2000 Inland Revenue press release that introduced it, IR35 has been significantly reformed and remains one of the most contentious areas of UK tax law for contractors and freelancers.

Why IR35 Exists

When a worker provides services through a personal service company (PSC) or limited company rather than as a direct employee, they can take salary plus dividends — paying significantly less tax than an equivalent employee. IR35 aims to ensure that workers who are effectively employees cannot use a limited company structure to avoid the tax and NI that employment attracts.

If HMRC determines you are "inside IR35," the income from that contract is treated as deemed employment income — taxed as salary with full income tax and NI, eliminating the advantage of the company structure.

The Three Key Tests

HMRC uses a multi-factor assessment based on established employment case law. Three tests carry the most weight:

1. Substitution Can you send a substitute to do the work in your place? If yes, and the client would genuinely accept the substitute without needing to approve them individually, this strongly indicates a genuine business-to-business relationship (outside IR35). If the client requires you personally to show up, this indicates employment.

2. Control Does the client control how, when, and where you work — or are you free to determine your own working methods? High control (set hours, must use client equipment, supervised daily) points to employment. Low control (you determine approach, work wherever, unsupervised) points to outside IR35.

3. Mutuality of Obligation (MOO) Is the client obliged to offer work and are you obliged to accept it? Mutual obligation is the hallmark of employment. If there's no obligation on either side — you complete a specific project and neither party is obliged to continue — this points away from employment.

Other Relevant Factors

Financial Impact: Inside vs Outside IR35

Scenario: £600/day rate, 220 days/year = £132,000 gross

Being inside IR35 costs approximately £28,480/year in additional tax on this example.

Who Determines Your IR35 Status?

Since April 2021, the responsibility for determining IR35 status shifted from contractors to their clients (end-users):

• Medium and large private sector clients must assess status and provide a Status Determination Statement (SDS)
• Small companies (under 50 employees, under £10.2m turnover, under £5.1m balance sheet) — contractor's limited company remains responsible for its own status determination
• Public sector — client has always determined status since April 2017

If You're Assessed as Inside IR35

Your client's payroll deducts income tax and NI from your contract rate via PAYE, treating the payment as deemed employment income. The company "wrapper" provides almost no benefit — you incur corporation tax on any amounts not extracted as deemed employment income.

Options when placed inside IR35:

1. Negotiate a higher day rate to compensate (clients sometimes pay a "gross-up")
2. Work through an umbrella company instead of a PSC
3. Genuinely change your working practices to move outside IR35
4. Challenge the SDS (you have the right to dispute)

Protecting Yourself Outside IR35

1. Written contracts: Ensure your contract clearly reflects genuine outside-IR35 working practices. A strong substitution clause, clear project scope, and no specification of working hours are key.

2. Practice matches contract: HMRC looks at actual working practices, not just contract wording. If you're required to work 9–5 at the client's office every day, your contract's substitution clause won't save you.

3. Get an SDS in writing: From medium/large clients, always receive the Status Determination Statement before starting. If you disagree, raise a formal dispute within the 45-day window.

4. HMRC CEST Tool: HMRC's Check Employment Status for Tax (CEST) tool at tax.service.gov.uk is HMRC's preferred assessment method. If CEST returns "outside IR35," keep the result as evidence.

5. IR35 insurance: Specialist insurers offer policies covering HMRC investigation costs and any tax liability found — typically £300–£1,500/year depending on cover level.

6. Multiple clients simultaneously: Working for multiple clients at the same time strongly evidences business operation rather than disguised employment.

Frequently Asked Questions

Q: My client says I'm inside IR35 — can I appeal? Yes. You have the right to dispute the Status Determination Statement. Submit a written disagreement; the client must respond within 45 days. If the response is unsatisfactory, escalate to HMRC or seek legal advice.

Q: Can I be inside IR35 for one client but outside for another? Yes. IR35 status is assessed contract-by-contract. A contractor can be inside IR35 for one engagement and outside for another simultaneously.

Q: HMRC's CEST tool returned "undetermined" — what does that mean? It means CEST cannot determine your status from the information provided. Seek independent advice from an IR35 specialist. Do not assume this is a safe result.

Q: Does IR35 apply to sole traders? No. IR35 specifically applies to workers providing services through a personal service company or similar intermediary. Sole traders are taxed as self-employed directly and IR35 is not relevant.