What is IR35 and does it apply to me?

IR35, officially the off-payroll working rules, is designed to stop people working like employees from paying less tax and National Insurance by working through a limited company. It looks at whether, if the intermediary company wasn't there, you'd effectively be an employee of your client, based on factors like control, substitution, and mutuality of obligation. Whether it applies to you depends on the specific working relationship and who your client is, so it's genuinely worth getting a professional assessment rather than guessing, since getting it wrong can be costly.