Self-Assessment Tax Return Mistakes and How to Avoid Them.


There are a number of common self-assesment / tax return mistakes that can hold things up (possibly leading to a penalty fee), cause you problems or even prompt HMRC to look more closely at you. So it’s best to be aware of them and make sure you don’t make them!

The easiest way to avoid all of these common tax return mistakes is to use a good Accountant (DNA obviously!!), we know how to avoid these errors:

  1. Incorrect figures

Double check any calculations to ensure you pay the correct amount of tax. Any deliberate wrongdoing can result in prosecution.

  1. Not declaring all income/Capital Gains

There are severe penalties for failing to declare all relevant income and Capital Gains. For deliberate errors, e.g. omitting a source of income on purpose, you could potentially be prosecuted.

  1. Trying to claim expenses that can’t be claimed

There are complex rules governing the what expenses you can deduct, and there are costly penalties for incorrect claims. It’s far better to check these things carefully – some things you may think can be claimed, can’t. But there are also a few things you may not have thought to claim.

  1. Signature & date

If you are submitting a paper return, make sure you sign and date it before you send it in. A photocopy will not suffice. This is a simple mistake, but people do forget to sign their tax returns.

  1. National Insurance number and Incorrect Unique Taxpayer Reference (UTR)

Make sure these are correct. The UTR is a ten digit reference number unique to you that will be on any correspondence you receive from HMRC. It’s important to include these and to get them right.

  1. Not enclosing supplementary pages

For additional income not covered by the main tax return, you will need to include supplementary pages. Additional information which may be relevant includes:

  • Life insurance gains
  • Stock dividends, non-qualifying distributions or close company loans written-off
  • Income from share schemes
  • Taxable lump sums from overseas pension schemes
  • Income from property


  1. Writing things like: “info to follow” or “as per accounts” instead of writing required figures

HMRC does not accept information like this. Include all the information that’s needed where it’s needed and when it is needed. Everything should be submitted together.

  1. Ticking wrong boxes

Use the guide HMRC includes with your tax return to help you. It’s very clear and takes you through the process step by step.

  1. Missing the deadlines

The deadline for submitting a paper return is 31 October following the end of the tax year. The deadline for filing your tax return online is 31 January after the end of the tax year. So a tax return for the 2015/16 tax year would need to be submitted online by 31 January 2017. If you miss the deadline, you will have to pay penalties which increase the longer you delay.

  1. Improper record-keeping

You need to keep proper and complete records, such as:

  • Cash books
  • Invoices
  • Mileage records
  • Receipts
  • Bank statements

If you do make a mistake on your tax return you’ve normally got 12 months from the submission deadline to correct it. This is called an ‘amendment’. For example, for the 2015/16 tax year you have until 31st January 2017 to file your tax return online. If you subsequently notice that you have made a mistake on this return, you have a further 12 months, which takes you up to 31st January 2018, to correct the error with an amendment.

As you can see it can get complicated, if you are in any doubt then let us deal with your Self-Assessment Tax Return for you, we will make sure it is correct. Get in touch.

DNA Accountants

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