When do I have to register As Self Employed? It’s important to tell HMRC that you are self-employed as soon as possible. If you don’t, you may have to pay a penalty. You don’t want to pay more to HMRC than you have to as it is a waste of your money. Your business has started when you start to advertise or you have a customer to buy your goods or services. It is at this point that your business is ‘trading’. You cannot register before you start trading. For example, if you advertise your business in the local newspaper on 15 January but do not get your first customer until 29 March; in this case, you have been trading since 15 January. You must tell HMRC within six months of the end of the tax year in which you start self-employment.