IR35 without the panic

Maybe it was a hiring manager, mid-negotiation. Maybe it was a client's HR team, sending over a contract with a clause you don't recognise. Either way, you've just incorporated (or you're about to) and suddenly there's a piece of tax legislation from the year 2000 standing between you and knowing what you'll actually take home.

You're not alone in finding this confusing. Most of what people run into today as "IR35" isn't the original legislation at all — it's the off-payroll working rules, a 2021 reform that changed who's responsible for figuring out your tax status. And this year, the rules shifted again.

What this guide won't do: it won't give you a legal determination on your specific contract. Nothing short of a professional review or HMRC's own tools can do that reliably (and even those have gaps). What it will do is make sure you're asking the right questions

The basics: IR35 the legislation vs. "inside/outside" the status

The single most common confusion is treating these as the same thing. They're not.

IR35 is the umbrella term for the tax rules, originally introduced in the Finance Act 2000, designed to catch "disguised employment." That's HMRC's term for someone doing a job that looks, in practice, like employment, while being paid through a limited company in a way that's more tax-efficient than being on payroll.

Inside or outside IR35 is the status a specific contract gets, once assessed against that legislation. This is the part that actually affects your money. It's assessed per contract, not once for you as a person or for your company as a whole. You can be genuinely outside IR35 on one engagement and inside on the very next one, even with the same skills and the same limited company.

Your company doesn't have an IR35 status. Your contracts do.

This is why "I've got a limited company, so I'm outside IR35" is one of the most common (and most costly) assumptions new contractors make.

The core tests: what actually gets assessed

Strip away the legal language and the tests come down to three everyday questions about how the work actually happens.

1. Control: Does the client dictate how, when, and where you do the work, the way a manager would with an employee? Or do you decide your own method and schedule, and just deliver the agreed outcome?

2. Substitution: Could you, in practice, send someone else to do the work in your place? A genuine, unfettered right of substitution is one of the strongest indicators of being outside IR35

3. Mutuality of obligation: Is the client obliged to keep offering you work, and are you obliged to accept it? Employment relationships have this; a genuine contract-by-contract engagement shouldn't.

HMRC provides a free tool - Check Employment Status for Tax (CEST) - to help work through these questions. If you use it and keep a record of your answers, HMRC will generally stand by the result, which counts as evidence of reasonable care.

What it means for your money: inside vs outside

Inside IR35: you're treated as an employee of the end client for tax purposes. PAYE applies, that means your fee-payer deducts Income Tax and National Insurance at source, before you ever see the money. Take-home pay typically drops by 20–30% compared to the same gross contract value outside IR35.

Outside IR35: your limited company receives payment gross. You manage your own tax position (salary, dividends, expenses, corporation tax) with all the planning flexibility (and responsibility) that comes with running a company properly.

Why this matters before you sign: the difference isn't just a tax technicality - it changes your cash flow, your admin burden, and what rate you should actually be negotiating for. A contract that looks attractive at face value can be materially worse once you factor in an inside-IR35 determination.

Checklists worth five minutes of your time

Red flags in the contract or the working pattern:

1. The client controls how the work gets done, not just what's delivered.

2. No genuine right of substitution written into the contract.

3. Fixed hours, client-supplied equipment, or day-to-day integration into the client's team (email address, appraisals, staff socials.)

4. An open-ended, rolling engagement with no clear end point or deliverable.

Staying on top of it

This isn't a one-time check. Your status can change from contract to contract. And none of this happens in isolation from the rest of running your company — your accounts, your filings, your other admin.

This guide is for general information only and isn't a substitute for professional tax or legal advice on your specific circumstances.