How IR35 affects contractors is one of the most common questions I get, and honestly, it’s not surprising. The rules are genuinely complicated, the official guidance can feel like it was written in a different language, and the financial consequences of getting it wrong are real.

What IR35 Actually Is (In Plain English)

IR35, or the off-payroll working rules, exists because HMRC wants to make sure contractors who work like employees pay broadly the same Income Tax and National Insurance as employees. The question it tries to answer is this: if you took away your limited company and provided your services directly to the client, would you look like an employee? If the answer is yes, HMRC says the IR35 rules apply to you.

The rules sit under what HMRC calls the off-payroll working rules, and they’ve been around in some form since 2000. They were tightened significantly for public sector contractors in 2017, then extended to medium and large private sector clients in April 2021. If your client is a small business outside the public sector, the responsibility for assessing your status falls on your own intermediary, usually your limited company.

Inside vs Outside IR35: What the Difference Costs You

If a contract is outside IR35, you’re treated as a genuine contractor. You can take a salary and dividends through your limited company in the usual way, keeping your tax bill lower than if you were employed. If a contract is inside IR35, the rules say you should be taxed more like an employee, which means more Income Tax and National Insurance is deducted from the fees your company receives.

The financial gap between inside and outside IR35 can be significant. Research from the contracting sector shows that 81% of contractors increase their day rates when they accept inside IR35 engagements, which tells you everything about the real-world cost. It’s worth knowing that if you’re inside IR35, the party paying your company (the deemed employer) has to deduct Income Tax and employee National Insurance from those fees, and also pay employer National Insurance on top.

How Your IR35 Status Gets Decided

Three key tests sit at the heart of any IR35 determination. The first is supervision, direction, and control: does the client control how you do your work, or just the end result? The second is mutuality of obligation: is there an expectation that the client will keep offering work and you’ll keep accepting it? The third is the right of substitution: could you send a suitably qualified replacement to do the job if you weren’t available?

HMRC has its own online tool called CEST (Check Employment Status for Tax), and while it can be a useful starting point, it has well-documented limitations. Courts and tribunals have decided cases differently to CEST in the past. The honest truth is that both the contractual wording and your actual working practices matter, and the two have to line up. A contract that says you have a right of substitution but you’ve never once exercised it, and the client would never accept it, won’t hold up under scrutiny.

What’s Changed in 2026 and Why It Matters

From 6 April 2026, new PAYE rules apply to labour supply chains that include umbrella companies. If you’re operating through an umbrella company, the agency or end client in the chain now carries liability for ensuring the umbrella runs PAYE correctly. HMRC can recover unpaid tax from them if the umbrella fails, which has made many clients and agencies nervous about umbrella arrangements.

A survey of 700 contractors found that 69% couldn’t confirm whether their umbrella company was compliant, and 50% reported unexpected deductions. The good news on the IR35 side is that the picture has actually improved: recent data suggests 78% of Status Determination Statements result in outside IR35 outcomes, and the Supreme Court has resolved some of the case law uncertainty that had been hanging over the sector for years. If you’ve been worrying that IR35 has made contracting pointless, that’s not the picture on the ground for most contractors.