Prepare now for the self-assessment tax deadlineTen tips to making a successful online tax return

14 November 2012

Making an online tax return is straightforward but you need to register in good time and plan ahead to meet the 31 January deadline. We explain how file online successfully and avoid a £100 fine.

Making an online tax return

The deadline for filing a paper tax return (31 October) has now passed. If you are filing online for the first time, follow our 10-step plan to submitting a successful tax return:

1. Check you are eligible to make a self-assessment tax return. HMRC should have written to you in April. If in doubt, call the self-assessment Helpline on 0845 900 0444 or write to HM Revenue & Customs, Self Assessment, PO Box 4000, Cardiff, CF14 8HR.

2. Before you start, you need to know your ten-digit 'Unique Taxpayer Reference' (UTR). HMRC should have issued this. If you don't know it, contact the telephone helpline and they will send it by post to your home address. They can't tell you it over the phone. You will also need your National Insurance number.

3. To file online for the first time, you need to register to use HMRC Online services. Log on to their website ( and select 'Self Assessment'.

4. To set up an online account, you need to create a password and receive a User ID. The User ID will be sent to you online. Make sure you keep a note of this as you will need it to log on. If you forget the User ID, you can get HMRC to send it again by email or post. They can also issue a replacement password if you forget this.

5. You will be sent an activation code by post. This is similar to the security code issued by credit card providers. It takes about a week to arrive, so make sure you leave enough time.

6. When you receive the code, log on and activate your account. Make sure you do this within 28 days of receipt, or the code will expire and you'll have to request another one.

7. Filing an online tax return is very similar to completing a paper one (SA 100). The main difference is that supplementary pages are added as you go, rather than having to be ordered in advance. Online notes appear as you complete each question (hold your cursor over the box) rather than in a separate guide.

8. Before you start to enter figures, make sure you have all the information you need. Most commonly this includes:

  • employment details (P60 or P45)
  • pension contributions or receipts
  • income from letting property or land
  • capital gains or losses
  • income from UK savings & investments
  • life insurance gains and AVC refunds
  • any other taxable income
  • gifts to charity (if claiming tax relief)

If you don’t have exact figures, you can submit an estimate or a provisional figure. Explain how you arrived at your totals in the 'Additional Information' section and why you can't use actual figures. Estimated figures are acceptable if waiting for final ones would make you miss the self-assessment deadline.

9. Save your online return as you go - you don’t need to complete it all in one session. In cases of difficulty, there is an HMRC Online services telephone helpline (0845 60 55 99). Once you are ready to submit a return re-enter your user ID and password. You can print off your return to keep a hard copy.

10. HMRC will immediately acknowledge receipt of your online tax return.   

More on this...

  • The Which? tax calculator- check your likely 2012 tax bill
  • 2011-12 tax returns- deadlines and details for submitting your tax return
  • Late tax returns- what happens if you miss the HMRC tax return deadline