IR35 is genuinely complicated, and HMRC’s own guidance contradicts itself in places, so feeling uncertain about your status is not a personal failing. This guide explains how the off-payroll working rules apply to limited company contractors, what determines your status, and what you should do if you have received an inside-IR35 determination.

Why IR35 still matters for limited company contractors in 2026

The off-payroll working rules exist to ensure that workers providing services through their own limited company pay broadly the same Income Tax and National Insurance as employees, if they would have been an employee had they contracted directly. HMRC’s own guidance confirms that the rules apply when the client, the engagement, and the working arrangements together resemble employment. If you operate through a personal service company, this applies directly to you.

Since April 2021, medium and large private sector clients have been responsible for issuing a Status Determination Statement (SDS) before you start work. Where the client is a small business outside the public sector, the responsibility for determining status sits with your own intermediary. Getting this wrong in either direction carries financial consequences, which is why having a clear picture of your working practices is not optional.

Where most contractors go wrong with IR35

Most IR35 problems I see come down to one thing: the contract says one thing and the actual day-to-day working arrangement says something else. HMRC does not care what your contract says if your working practices tell a different story. The three factors HMRC weighs most heavily are supervision, direction and control (SDC), right of substitution, and mutuality of obligation.

Relying on the CEST tool result as final

HMRC’s Check Employment Status for Tax (CEST) tool gives a result based on the answers you enter, but it does not cover every scenario and is not legally binding. If you input inaccurate information, whether through misunderstanding a question or wishful thinking, the result is worthless and offers no protection in an investigation. The tool is a useful starting point, not a defence.

Not keeping records of actual working practices

Even if your contract is written correctly, HMRC can challenge a determination by looking at how the engagement actually operates. If you attend the client site every day, take direction from a line manager, and have never exercised a right of substitution, those facts will override your contractual terms. Keeping a brief contemporaneous record of how you exercise your independence gives you a factual basis to defend your status.

What to do with your IR35 status, step by step

Whether you have just received an inside determination, are about to sign a new contract, or have never had a formal review, the process is the same. Work through these steps in order rather than trying to fix the most urgent thing first.

1. Step 1: Review your current contract against the three core IR35 indicators. Check whether your contract clearly reflects a right of substitution, the absence of mutuality of obligation, and your freedom from supervision, direction and control. If your contract was drafted by the client or an agency, it may not protect you even if your working practices are correct.
2. Step 2: Compare your contractual terms against your actual working practices. Write down honestly how the engagement operates day to day. If there is a gap between what the contract says and what you actually do, that gap is where HMRC will focus. Address it before an investigation rather than after.
3. Step 3: Obtain or request a Status Determination Statement from your client if they are a medium or large business. The client is legally required to provide one and must give you reasons for the determination. If you disagree with an inside determination, you have the right to formally dispute it through the client’s disagreement process.

If you have been operating for some time without a formal review, a retrospective status assessment is the right place to start. Many contractors find they have been trading correctly all along and simply need the paperwork to confirm it. Others need to adjust their working practices or contract terms before their next engagement.

The financial reality of inside versus outside IR35

The difference in take-home pay between an inside and outside IR35 engagement is significant. When a contractor is inside IR35, the deemed employer deducts Income Tax and employee National Insurance from fees paid to the intermediary, and also pays employer National Insurance on top. Analysis from IT Contracting puts the combined tax and National Insurance burden at around 45% for basic rate taxpayers and up to 60% for higher rate taxpayers. The same survey of 700 contractors noted that 81% of contractors increase their rates when taking an inside IR35 engagement, which is a rational response to the higher tax cost.

How to get your IR35 position sorted today

The most common reason contractors stay in a state of uncertainty about IR35 is that they do not know where to start. The answer is always the same: start with your current contract and your current client. Everything else follows from there. If you are between contracts, now is the right time to review before you sign anything new.

• Pull out your current or most recent client contract and check whether it explicitly covers substitution rights, the absence of mutuality of obligation, and your freedom from day-to-day supervision. If it does not, note the gaps before your next conversation with a client or agency.
• Book a free introductory call with David to walk through your specific situation. You will get a clear picture of where you stand, what the risks are, and what a contract review would involve. There is no obligation and no tie-in.