The SA101 is one of the supplementary forms that you can attach to the SA100 main Self Assessment tax return form if you need to declare less common types of income, deductions, and tax reliefs.

For example:

• If you earned interest from gilts (UK government bonds)
• If you paid tax in another country and want to claim tax relief
• If you invested in a VCT or SEIS/EIS startup and want to claim tax relief for your investment, etc

You can download the SA101 from HMRC’s website. Just like with the main SA100 form, you don’t need to file the SA101 if you file your tax return online.