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Why you might need to complete a tax return

If your circumstances change you may need to fill in a Self Assessment tax return. On the return you tell HMRC about income or capital gains, or claim expenses or reliefs. For example, you may have:

• started your own business
• untaxed income from property or investments
• expenses to claim (you need a tax return if they are above £2,500)
• Capital Gains Tax to pay
  

• Do you need to complete a tax return?

• Capital Gains Tax

Why and when you need to register for Self Assessment

You need to register for Self Assessment before you complete your first tax return.

When you register you will give HMRC the information they need to set up the right records for you. This helps to make sure you pay the right amount of tax and National Insurance at the right time.

For other changes in circumstances, simply complete the relevant boxes or supplementary pages on your Self Assessment tax return.

When to register

It’s best if you register with HMRC as soon as your circumstances change. The latest you should register is by 5 October after the end of the tax year for which you need a tax return. The tax year runs from 6 April one year to 5 April the next.

If, for example, you have tax to pay on rent from a property in the 2011-12 tax year, you need to let HMRC know by 5 October 2012.

If you register late you may have to pay a penalty.

Information you'll need before you can register

You will need:

• your National Insurance number. In most cases you'll already have this, but if you haven’t worked in the United Kingdom before you'll need to get one
• your contact details (and the contact details of your business, if you have started self-employment)
• your ten-digit Unique Taxpayer Reference number - but only if you have previously completed a Self Assessment return. You’ll find this on previous letters or forms sent by HMRC about your tax return
• the date your circumstances changed
  

• Applying for a National Insurance number

How to register

If you are an employee or aren't working, you should complete and send in form SA1 Registering for Self Assessment

If you are self-employed, joining a partnership or are setting up a new partnership the forms you need are different. Follow the second link below and read the section 'How to register' on the HMRC website.

• Get form SA1 Registering for Self Assessment Opens new window

• Register your business for Self Assessment Opens new window

What happens once you have registered for Self Assessment

Getting a reference number

HMRC will set up your records and send you a letter with a ten-digit reference called a Unique Taxpayer Reference or UTR. You should keep your Unique Taxpayer Reference in a safe place.

Getting online

Once you have received your reference number, you need to sign up for HMRC Online Services, before you can send your Self Assessment tax return online.

• File your tax return online

• Telephone or write to HMRC Opens new window

Sending your first tax return

You'll get a letter, usually in April, telling you when you need to send your first tax return. HMRC may get in touch earlier if you need to send a return for a previous tax year. If you don't receive a letter or a tax return, you should contact HMRC.

• File your tax return online

• Telephone or write to HMRC Opens new window

Useful contacts

• Self Assessment and your tax return