Self Assessment is a system that HMRC uses to collect Income Tax from:sole traderspeople with more than 1 source of incomecompany directors who take dividendsanyone earning more than £100k/yearDetails of the year’s earnings from 6 April-5 April need to be submitted to HMRC by 31 January in the following year. The tax is due in two instalments: 31 January (in arrears) and 31 July (in advance). You can read more about this in our blog on how to do a self-assessment return.