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 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

File your tax return online or call HMRC and request form SA100.


Send your tax return by the deadline.

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. Check how to register 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.

How much tax you pay will depend on the Income Tax band you’re in. There’s a different rate for Capital Gains Tax if you need to pay it, for example you sell shares or a second home.