Register with HMRC as soon as possible after you become self-employed. A penalty may be charged if you fail to do so by 5 October (for tax purposes) or 31 January (for national insurance contributions) after the end of the tax year in which you started the business. You can register through your personal tax account or by ringing the self-employed helpline (0300 200 3300; Textphone 0300 200 3319). You will be asked to complete a tax return each year. You can find more information at www.gov.uk/working-for-yourself .