Once you have registered with HMRC for Self Assessment, they will send you a Unique Taxpayer Reference number. You can use this to send an annual Self Assessment tax return, either online or using a postal SA100 form. If you do use the postal form and have self-employed income, you will also need to complete a SA103 form. This is the part of the tax return that deals with self-employed earnings.
How often do I need to tell HMRC about my self-employment?
Usually you will only need to update HMRC using your annual Self Assessment tax return once a year, unless something changes. If anything does change in the middle of the year, such as change in the structure of your business, or you cease trading, you will need to let them know.
If you’re a partner in a partnership, you’ll also need to ensure that the partnership submits a tax return. Each partner is also required to submit their personal Self Assessment, too.
Once you have completed and submitted form SA103 to HMRC you will receive a Statement of Account showing the amount of tax you owe, the tax you have already paid and the final amount of tax owing. All income tax and National Insurance should be paid in full by 31st January each year. This is also the filing deadline for submitting your tax return online. The deadline for a paper tax return is 31st October each year.