Self assessment registration deadline 5 October
If you need to complete a self assessment return, it is your responsibility to register with HMRC. Self assessment typically applies if you are self-employed, have a high income or have complicated tax affairs. You can use an online tool to check whether you need to register.
You must register by 5 October after the end of the tax year. For example, if you need to complete a tax return for the tax year 6 April 2020 – 5 April 2021, you must register by 5 October 2021.
If you already completed a self assessment return last year, there is no need to register again this year. HMRC should automatically remind you of the need to complete a return (but it is your responsibility whether they remind you or not).