Self Assessment is the system HMRC uses in the UK to collect income tax from individuals whose income isn't taxed at source (e.g., through PAYE). If you earn income outside of regular employment, you may be required to complete a Self Assessment tax return.You will need to file a Self Assessment tax return if you:
Are self-employed or a sole trader
Have income from renting out a property
Have income from investments, such as dividends or interest
Have made capital gains from selling assets, such as property or shares
Have income from abroad
Need to pay the High Income Child Benefit Charge
Have income above a certain limit