If you are a sole trader, you’ll need to register for self-assessment before October 5 in your second trading year. Once this has been completed you’ll need to fill in your tax return each year, which you can do on your own or be supported by an accountant. The deadline for the tax return is normally at the end of January. If you miss this deadline you may have to pay a fine. Once you’ve registered you’ll also get a Unique Taxpayer Reference (UTR), so keep this safe.