Self Assessment is a system HM Revenue and Customs (HMRC) uses to collect Income Tax.
Tax is usually deducted automatically from wages and pensions. People and businesses with other income (including COVID-19 grants and support payments) must report it in a tax return.
If you need to send a Self Assessment tax return, fill it in after the end of the tax year (5 April) it applies to.
You must send a return if HMRC asks you to.
You may have to pay interest and a penalty if you do not file and pay on time.
This guide is also available in Welsh (Cymraeg).
Sending your return
You must tell HMRC by 5 October if you need to complete a tax return and you have not sent one before. You could be fined if you do not.
You can tell HMRC by registering for Self Assessment.
Filling in your return
You need to keep records (for example bank statements or receipts) so you can fill in your tax return correctly.
You can get help filling in your return.
Paying your bill
HMRC will calculate what you owe based on what you report.
Pay your Self Assessment bill by 31 January.