The Self Assessment is the tax return you must complete each year if you are self employed. It is made up of the main form (referred to as the SA100) and a number of supplements. The form SA103 is the Self Employment supplement to the self assessment.
The Self Assessment is used to calculate how much Income Tax and Class 4 National Insurance you need to pay.
It can be filled in online or a paper copy can be completed.
The paper copy will disappear with the introduction of the flagship “Making Tax Digital” project.
Even if the profits you make from your self employed business fall below the annual personal allowance (the amount you can earn before you have to pay tax) you still need to complete a self assessment.