If you work as a contractor or freelancer through your own limited company, you've probably heard of IR35. These off-payroll working rules are designed to make sure that someone who works like an employee pays broadly the same tax and National Insurance as an employee. The rules can feel complex, but with a bit of preparation you can approach each assignment with confidence.

What IR35 actually means for you

IR35 is not a tax in itself. It's a set of rules that look at whether your limited company arrangement is a genuine business-to-business relationship or a disguised employment. If HMRC decides you would have been an employee if you'd been hired directly by the client, then your company must calculate tax and National Insurance as if you were employed. That means less take-home pay and more paperwork.

The rules apply differently depending on your client. For public sector clients and medium or large private sector clients, the client decides your status and issues a Status Determination Statement. Small private sector clients are exempt, so your limited company remains responsible for deciding status. A small company must meet two of three criteria: annual turnover under £10.2 million, balance sheet under £5.1 million, or fewer than 50 employees.

Inside versus outside IR35: the practical differences

When you're inside IR35, your company pays income tax and National Insurance through PAYE on most of the income from that contract. You can still claim some expenses, but the old 5% allowance for administration costs is gone for contracts caught by the off-payroll rules. You might also find that the client or an umbrella company deducts tax before paying you.

When you're outside IR35, you operate as a genuine business. You invoice the client, pay corporation tax on profits, and take dividends. You have more control over your tax planning. The key is that your working practices must match your contract. A contract that says you're outside IR35 means nothing if the day-to-day reality says otherwise.

The three pillars of status: control, substitution, and mutuality of obligation

HMRC and tribunals look at many factors, but three are especially important:

• Control: Does the client tell you what to do, how, when, and where? If they supervise your work like a manager, that points towards employment. If you decide how to complete the work, that points towards self-employment.
• Substitution: Can you send someone else to do the work? A genuine right of substitution, without needing the client's permission, strongly suggests you're outside IR35. If you must do the work personally, that's a sign of employment.
• Mutuality of obligation: Is the client obliged to offer you work, and are you obliged to accept it? A series of rolling contracts with no end date can look like employment. A project with a clear deliverable and no guarantee of further work is more likely outside IR35.

How to review your contracts and working practices

Before you accept an assignment, read the contract carefully. Look for clauses about control, substitution, and termination. But don't stop there. Your working practices matter just as much. Ask yourself:

• Do you have a manager who sets your hours and approves your leave?
• Are you integrated into the client's team, attending staff meetings and using their equipment?
• Do you bear any financial risk? For example, do you have to fix mistakes at your own cost?
• Can you work for other clients at the same time?

If the answers point towards employment, you may be inside IR35 even if your contract says otherwise. Keep evidence of your independence: your own insurance, your own equipment, multiple clients, and a clear project scope.

What to do if you're caught inside IR35

If a client issues a Status Determination Statement saying you're inside IR35, you have options. You can accept the determination and let the client or their payroll partner deduct tax. You can request a review if you disagree. Or you can walk away from the contract. If you stay, make sure you understand how your pay will be calculated. For medium and large clients, they must deduct PAYE and National Insurance before paying your company or an umbrella company. You won't be able to claim the 5% expenses allowance, but you can still claim allowable expenses like professional subscriptions and travel to temporary workplaces.

Practical steps to protect your position

IR35 doesn't have to be a headache. Take these steps for every engagement:

• Get your contract reviewed by an IR35 specialist before you sign. A few hundred pounds now can save thousands later.
• Keep a written record of how you actually work. Note examples of you deciding your own methods, providing your own tools, and turning down other work.
• Use HMRC's Check Employment Status for Tax tool as a starting point, but don't rely on it alone. It doesn't cover every situation.
• Consider taking out tax investigation insurance. It can cover the cost of professional representation if HMRC asks questions.
• Review your status regularly. A contract that was outside IR35 last year might drift inside if your working practices change.

Remember, IR35 is about the reality of the working relationship, not just the label on the contract. By staying informed and reviewing each assignment carefully, you can keep your business on solid ground.