The SA103 is a form that you need to attach to your SA100 main Self Assessment form if you need to pay tax on income from self-employment.

How do you know if you need to fill an SA103?

You’re self-employed (also called a “sole trader”) if:

• You’re working for yourself as a freelancer
• But not if you’re full-time employed (although you should check with your employer to make sure)
• And not if you’re a director of your own limited company (you’re technically an employee of your own business)

There are two versions of the SA103:

• SA103S (“the short version”): you can use this one if your income from self-employment was less than £85,000
• SA103F (“the full version”): if you earned more than £85,000 from self-employment

You can download the SA103 on HMRC’s website. Similar to the main SA100 form, you only need to print it and mail it if you don’t do your file return online.