Introduction to Self Assessment

Self Assessment involves completing a tax return each year. You show your income and capital gains (profits on the sale of certain assets) and claim tax allowances or reliefs on your tax return. This guide covers how to get a tax return, when to send it back and what happens if you don’t.

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Who needs to complete a Self Assessment tax return?

Not everyone needs to complete a tax return. If your tax affairs are straightforward you may already pay all of the tax due on your earnings or pensions through your tax code.

But you may need to complete a tax return if you have more complicated tax affairs, even if you already pay tax through your tax code. There are also certain circumstances in which you will always need to complete a tax return - for example if you're:

  • self-employed
  • a company director
  • a trustee
  • receiving foreign income

Tax returns - do you need to complete one?

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How to get a Self Assessment tax return

You need to register for Self Assessment before you can get a tax return. HM Revenue & Customs (HMRC) will use the information you provide to set up the right records for you. They will then send you a ten-digit tax reference, called a Unique Taxpayer Reference. You'll need to keep this safe.

HMRC will send you a letter each year, usually in April or May, telling you to complete your tax return. If you haven't received this letter or a tax return by the end of May, you should get in touch with HMRC.

You can send your tax return online or on paper. There are lots of benefits to sending it online. It's quick, easy and you have three months longer to send it. See the section 'sending your tax return online' below.

Find out how to register for Self Assessment

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Tax return deadlines and penalties

If you send in a paper tax return, it must reach HMRC by midnight on 31 October. If you miss this deadline you should send your return online

If you send in your tax return online it must reach HMRC by midnight on 31 January. You'll have to pay a £100 penalty if HMRC doesn't receive your tax return on time. The later you send your return, the more penalties you're likely to pay.

Follow the link below to find out more about:

  • penalties for sending your return late
  • interest and penalties for paying your tax late
  • exceptions to the deadlines above

Find out more about tax return deadlines and penalties

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Sending your tax return online

Sending your tax return online has many advantages. For example your figures are calculated automatically and you'll know right away what you owe or what HMRC owes you. Most tax returns can be sent online.

You need to sign up for HMRC Online Services first. Once you've signed up, you can use HMRC's free Self Assessment service or you can buy commercial software to send your tax return.

The free HMRC service doesn't provide certain tax returns online and you must use commercial software instead. These include:

  • Partnership Tax Return
  • Trust and Estate Tax Return
  • some pages that support the main tax return, such as those for Lloyd's members and ministers of religion

File your tax return online - find out more

Tax returns you can't send online

There is currently no commercial software or HMRC service for the following tax returns:

  • SA700 - Non-resident Company Tax Return
  • SA970 - Trustees of Registered Pension Schemes

You have to send these on paper instead. However, the deadline is the same as for online returns - 31 January.

Find the Self Assessment forms you need

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