Q: When do we need to notify HMRC of the need to complete our first Self Assesment Return?
A:By 5th October following the end of the Tax Year in which you acquired a new source of income.(Example a new house or flat acquired to let out )
You commence a business on 1 January 2016
This means there is a new source of income in the Tax Year 6 April 2015 to 5 April 2016 (2015/2016)
You need to inform HMRC by 5 October 2016 for your need to complete a Self Assessment Return for the Tax Year 2015/16