Common mistakes to avoid on your Self Assessment tax return

By Jake Martin

2 min read

If you’re planning to send a paper Self Assessment tax return this year, make sure you get it right, as mistakes will cause delays.

According to HMRC, these are the most common issues to watch out for.

  • Sign and date the tax return – forgetting this is easily done so don’t forget to check
  • Supplementary pages – double-check whether any are required and that you’ve included them
  • Tax reference number – don’t forget to add this if you downloaded the form
  • Correct form – you must use the right form for the right tax year – you can’t just change the date on an old form
  • Tax return notes – HMRC advises avoiding putting notes on the return like ‘information to follow’
  • Filing late – Don’t forget, the deadline for filing paper Self Assessment tax returns is 31 October. 


If you miss the deadline for sending in your paper tax return, you should send it online instead – you have until 31 January. If you do still send a paper tax return and it reaches HMRC after the 31 October deadline, you’ll have to pay a £100 penalty.

Filing your Self Assessment tax return online

You can avoid many mistakes by sending your tax return online – the deadline is 31 January. The majority of businesses now file online and HMRC is encouraging more to do so. You should be aware of the following:

  • You’ll need to register to use HMRC Online Services to send your tax return online.
  • Make sure you know what your User ID and password is and don’t leave it until the last minute to check
  • Read any error messages, for example you may have used text or punctuation that aren’t accepted

De-stressing Self-Assessment

Getting help and support will take much of the stress out of completing your Self-Assessment return:

  • Make use of the help and guidance provided by HMRC – they have a number of guides andwebinars that should help you understand what you need to do
  • Use the services of an accountant – it will probably cost less than you think to have a few burning questions answered and get peace of mind that your tax return is completed correctly.
  • Take advantage of free tools out there designed to help you, such as the Intuit MyBizTracker app. As well as recording income and expenses and tracking receipts, MyBizTracker keeps an eye on key dates for you, so you don’t have to worry about forgetting an important deadline. It’ll let you know when your Self-Assessment tax return is due and warn you if you’re approaching the VAT registration threshold.

 Have you organised your 2011/12 Self-Assessment return yet? You might also find our Stress-free Self-Assessment guide for small businesses useful.

Information may be abridged and therefore incomplete. This document/information does not constitute, and should not be considered a substitute for, legal or financial advice. Each financial situation is different, the advice provided is intended to be general. Please contact your financial or legal advisors for information specific to your situation.

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