Correcting mistakes in your tax return

Mistakes happen and where a mistake has been made in your tax return it is possible to file an amended return to correct the mistake.

Amendment window

The amended return must be filed within 12 months of the original deadline.

The normal deadline for filing a self-assessment tax return online is 31 January after the end of the tax year. The self-assessment return for 2015/16 should have been filed by 31 January 2017. The filing deadline is extended where the notice to file was issued within three months of the filing deadline. Where this is the case, a later deadline of three months from the issue of the notice to file applies (so if the notice to file a 2015/16 tax return was given on 15 November 2016, the return must be filed by 15 February 2017). Paper returns must be filed by 31 October after the end of the tax year – so a deadline of 31 October 2016 for 2015/16 paper return.

Thus, where the normal online filing deadline applies, amended returns for 2015/16 must be filed by 31 January 2018. Where a paper return is submitted, an amended paper return for 2015/16 must be sent to HMRC to arrive by 31 October 2017.

Amendment process – online returns

Where the original return was filed online, it is a relatively straightforward process to amend it online. The process is as follows:

• Login onto the self-assessment online account.
• Choose `Tax Return Options’ from the menu.
• Choose the tax year for the return which is to be amended.
• Go into the tax return, amend the pages that need correcting and file the return again.

Amendment process – paper returns

Where a paper return was filed, a mistake in the return can be corrected by downloading a new tax return and sending the corrected pages to HMRC. Write `Amendment’ on each page and make sure the taxpayer’s name and UTR is included.

Write to HMRC

Alternatively, you can write to HMRC with details of the corrections. If the window for filing an amended return has passed, you will need to write to HMRC to tell them of any corrections. A refund can be claimed up to four years from the end of the tax year to which it relates.

Changes to your tax bill

Correcting a mistake in your tax return may also change the amount of tax that you owe for that tax year. Where an amended return is filed online, the calculation is also updated. Within three days of filing an amended return, the tax account will also be updated. If you owe more tax, this, plus the associated interest, should be paid without delay. If you have paid too much, you can request a repayment online. However, HMRC warn that you should allow up to four weeks to receive it.