IR35 guide for contractors in 2026.

IR35 decides whether a contractor working through a limited company is taxed as an employee. Since 6 April 2021 medium and large private sector clients make that call and issue a Status Determination Statement, and the fee payer deducts PAYE. Small clients leave the decision, and the liability, with the contractor's own company.

What is IR35 and who does it apply to in 2026?

IR35 is the shorthand for the off-payroll working rules in Chapters 8 and 10 of the Income Tax (Earnings and Pensions) Act 2003. It applies when someone provides their work through an intermediary, almost always their own limited company, in circumstances where they would have been an employee if they had been engaged directly. HMRC's landing page for the regime is Understanding off-payroll working (IR35).

Two chapters run side by side, and confusing them is the single most common error we see. Chapter 8 is the original rule from 2000: the contractor's own company assesses status, calculates a deemed employment payment, and pays the tax. Chapter 10 is the off-payroll regime that reached the private sector on 6 April 2021: the client assesses status, and the party that pays the contractor's company (the fee payer, often an agency) operates PAYE. Which chapter you are in depends entirely on the size of the end client.

The rules bite hardest on IT contractors, interim finance staff, engineering consultants, locum clinicians and self-employed barristers who invoice through a company. If you are a genuine sole trader with no intermediary, IR35 does not apply to you at all, although employment status still does. Our sole trader accountants page covers that separate question.

Inside vs outside IR35: what is the actual difference?

Outside IR35 means the engagement is a business-to-business supply. The contractor's company invoices, pays Corporation Tax on profit, and the director extracts a mix of salary and dividends. Inside IR35 means the engagement is treated as employment for tax: income tax and employee National Insurance come off at source, and employer National Insurance plus the Apprenticeship Levy sit on top of the fee.

The last row in that table is the point most rate negotiations miss. An inside IR35 payment reaches the company having already suffered PAYE, so it is not company profit and cannot be paid out again as a dividend. A company with only inside IR35 work is an expensive envelope for money that has already been taxed.

Who decides your IR35 status in 2026?

For engagements with medium and large clients, the client decides. It must issue a Status Determination Statement to the worker and to the party it contracts with, state the conclusion, give reasons, and take reasonable care in reaching it. A blanket determination applied to every contractor in a department without looking at individual contracts is the classic failure of reasonable care, and it moves the liability back up the chain to the client.

The client must also run a status disagreement process. If you disagree with an SDS, you have the right to make representations, and the client has 45 days to respond with either a changed determination or reasons for keeping it. Missing that 45 day window is treated as a failure, and the client becomes the deemed employer.

For engagements with small clients, nothing moved in 2021. Your own company assesses status under Chapter 8, and if the answer is inside, your company operates PAYE on a deemed employment payment. Chapter 8 still carries the 5 per cent allowance for the cost of running the company, which Chapter 10 does not.

What is the small client exemption?

A client is small if it meets the Companies Act 2006 small companies regime, which turns on two of three conditions: annual turnover, balance sheet total, and average number of employees. The monetary thresholds in that regime were uplifted for financial years beginning on or after 6 April 2025, so a figure you were quoted in 2022 is no longer the test. Confirm the current numbers against HMRC's off-payroll guidance and the Companies House filing regime before you rely on it, because a client that was small last year may not be small this year.

Two practical consequences follow. First, client size can change mid-contract, and the rules give a transition point rather than an immediate switch, so the assessment obligation can move to the client from the start of the following tax year. Second, you can check the client's own filed accounts on the Companies House register rather than taking a project manager's word for it. We do this on every new engagement we review.

How does HMRC's CEST tool work, and should you trust it?

The Check Employment Status for Tax tool asks about substitution, control, financial risk and how the work fits the client's business, then produces a determination. HMRC has said it will stand behind a CEST result where the information entered is accurate and reflects the actual working practices. That conditional is doing a lot of work: a CEST run that describes a substitution right nobody would ever exercise is not accurate, and HMRC is not bound by it.

Use CEST, keep the printable output with the signed contract, and re-run it whenever the engagement changes shape. Then treat it as one piece of evidence rather than the whole case. The underlying tests come from case law, not from the tool: the personal service and substitution question, control over what, how, when and where, and whether there is mutuality of obligation. HMRC's reasoning is set out at length in the Employment Status Manual, which is the document that actually gets cited at tribunal.

What does being inside IR35 cost a contractor?

The honest answer is that it depends on your day rate and on who absorbs employer National Insurance. Employer NIC and the Apprenticeship Levy are a cost of the engagement, and in practice they come out of the assignment rate rather than being added to it. Current employer rates and thresholds are published by HMRC under rates and thresholds for employers, and they moved materially from 6 April 2025, so any comparison built on pre-2025 employer NIC is out of date.

A worked example, illustrative rather than a real client. A contractor on a 500 pound day rate for 220 days invoices 110,000 pounds outside IR35. The company pays Corporation Tax on profit after a small director salary and allowable costs, and the director draws the rest as dividends. Move the same engagement inside IR35 and the fee payer first covers employer NIC and the levy out of the assignment rate, then applies PAYE and employee NIC to what is left. The take-home gap on a mid-five-figure engagement is routinely five figures, which is why the determination is worth arguing about properly rather than accepting by email.

If your engagements are mostly inside, the case for keeping a limited company weakens and the case for an umbrella arrangement or direct employment strengthens. We model the comparison before anyone incorporates, which is one half of the decision covered on our company incorporation service page. The other half, the salary and dividend split when you are outside, sits with our accountants for freelancers and contractors.

How do you protect an outside IR35 position?

Contracts matter less than working practices, and working practices are what a tribunal examines. The clauses worth fighting for are a genuine and unfettered right of substitution, an absence of any obligation on the client to offer further work, and control that sits with you over how the work is done. The behaviours worth auditing are whether you appear on the client's internal org chart, whether you are managed through the client's line management process, whether you take company perks, and whether you are asked to cover work outside the statement of work.

• Keep a project-shaped statement of work. Deliverables and milestones, not a job description with hours.
• Invoice on delivery where you can. A rate per day worked, paid monthly in arrears with no notice period, reads as employment.
• Carry real financial risk. Fixed-price elements, your own equipment, your own professional indemnity cover, and rectification of defects at your own cost.
• Run more than one client where the work allows. Not decisive on its own, but it is evidence of being in business on your own account.
• Keep the paper. The SDS, the CEST output, the contract, the statement of work and any substitution correspondence, filed together for at least six years.

Locum medics and self-employed barristers face the same tests through a different lens, and the sector detail matters: see accountants for doctors and GPs and accountants for lawyers and barristers. Construction is different again, because payments there run through the Construction Industry Scheme first, which we cover on our construction accountants page and in the CIS scheme explained guide.

What happens if HMRC challenges a determination?

An enquiry usually opens with a request for contracts, invoices and the status determination for a named engagement. Where HMRC succeeds under Chapter 10, the deemed employer owes PAYE, employee NIC and employer NIC on the payments, plus interest and, where behaviour warrants it, penalties. Since 6 April 2024 HMRC can set off tax and NIC already paid by the worker and their company against that liability, which removes the double taxation that made pre-2024 settlements so punishing. It does not remove the employer NIC, the interest or the penalty exposure.

Two defensive habits pay for themselves. Re-paper the engagement whenever the scope changes, because a determination made against a contract that no longer describes the work is worth very little. And keep the tax cash separate: an inside determination applied retrospectively lands as a bill, not as a rate cut. Our Self-Assessment filing service and the MTD for Income Tax guide cover the personal return side of that, and the UK accounting service page sets out how we handle the company side.

IR35 guide for contractors: key dates and thresholds

One opinion, from doing this work: the biggest avoidable losses we see are not lost tribunals. They are contractors who accepted an inside determination without reading it, on an engagement that would have passed a proper review, and then priced the next three renewals off that number. Read the statement, use the disagreement process, and get the position on paper before the first invoice goes out. Terms you have not met before are defined in our accounting and tax glossary.