Avoid Self Assessment mistakes this month - top tips

The Self Assessment deadline is looming yet again. In just a few days, Moira Stewart will be peering down from billboards across the land, warning taxpayers that 31 January is on its way.

Inevitably, many self-employed people leave their tax return until the very last possible day – and this increases the potential for mistakes. But it is important that you make sure your Self Assessment is accurate if you are to avoid penalties.

When is my tax return due?

The day on which your Self Assessment tax return is due will depend on the way in which you file it. If you are filing online, it must reach HMRC by midnight on 31 January. If you file on paper, HMRC must receive it by midnight on 31 October.

Read more about Self Assessment deadlines.

What are the most common mistakes?

It can often seem as though HMRC has determined to make the Self Assessment process as deliberately opaque as possible. Certainly, filling in your tax return isn’t a fun task – and few people could argue that the Revenue has gone out of its way to make it simple. It should come as no surprise, then, that mistakes are fairly common. Here are some of the most frequent errors.

  • Missing pages. If you are filling your return in on paper, you need to make sure that you request all the relevant pages. Additional pages will be required if, for example, you are a trustee.
  • Missing digits. It is vital that you check all your figures before posting or hitting submit. Make sure you haven’t missed a zero off!
  • Missing signatures. If you are filing on paper, make sure that you sign and date the return properly before posting.
  • Failing to register. It is important to understand that you need to register for Self Assessment in order to be sent a tax return. You need to do this as soon as possible after becoming self-employed; failure to do so could result in a fine.
  • Failing to get logins. If you intend to file online, you need to register for a Government Gateway login. Remember that this takes around a week to arrive – so don’t leave it to the last minute.

How do I correct mistakes?

If you are concerned that you have made a mistake on a tax return you have already submitted, you need to act quickly in order to fix it.

You will normally be able to make an ‘amendment’ up to 12 months after the 31 January following the end of the relevant tax year. If you filed online, you can make an amendment by logging into Self Assessment Online. If you filed on paper, you need only complete and return the pages on which you want to make changes; you don’t have to redo the whole form. Make sure that you clearly mark the form ‘Amendment’ before sending it back.

If you want to correct a mistake made more than 12 months ago, you need to write to HMRC separately, giving them as much information about the change as possible. Remember that tax overpayments will usually only be repaid up to four years after the end of the relevant tax year.

Above all, you should make sure that you understand your legal responsibilities under the Self Assessment system. If you are in any doubt you should seek independent advice.