There is an online tool, developed by HMRC, that allows taxpayers to check if they need to notify HMRC about additional income. The online tool can be found at

You are required to submit a self-assessment return if any of the following apply:

You may also need to send a tax return if you have any untaxed income, such as:

There could be other reasons why you may be required to register for self-assessment and therefore using HMRC’s online tool can help you check if you are required to submit a return.

Source:HM Revenue & Customs | 03-06-2024