It’s a fairly common scenario so do not worry – follow the below steps and you’ll see it’s pretty simple to correct or amend a previous tax return.

How long do I have?

Most importantly, you have 12 months from the filing deadline in which to file an amended return.

So this means you have until 31 January 2020 to file an amended 2017/18 return where it was filed online.

But unfortunately this means if you have found a mistake in your return for 2016/17 or an earlier year, it is too late to file an amended return!
Instead, you need to write to HMRC and tell them about the error and advise them of the correct figures.

For HMRC’s address use this link.

How do I amend my tax return?

So at the time of writing this (April 2019) you still have time to file an amended tax return for 2017/18.

To do this, you need to log into your HMRC account and select ‘Self Assessment’ from the ‘at a glance’ page.
Under the heading of ‘tax returns’ it should say you have already completed your Self Assessment return for the 2017/18 tax year.

Now on this screen you’ll see a couple of options, including one to ‘Amend Self Assessment return for year 2017 to 2018’.
Select this option and you’ll then need to click on the scenario(s) which best describe the amendment(s) you need to make:

  • add a new section to your already submitted return e.g. a capital gain, or an additional employment
  • amend figures already submitted e.g. add additional expenses or income you received in the tax year
  • delete a whole section from your already submitted return

Once you click on the option that best describes the amendment(s) needed, just follow the instructions to correct the return in the right place.

But wait I filed a paper return!

You’ve got 12 months from 31 October (as an earlier deadline applies to paper returns!) to amend your return.
To amend a paper return, just download a new return, complete it correctly, and send it to HMRC. HMRC will then update/overwrite the info they hold on their system.

The tax amounts will change!

So by changing your tax return, there will likely be a change to either how much tax you should have paid, or what should have been refunded to you.

The bad news is that if you owed HMRC more tax they will apply a small amount of interest.
But the HMRC online portal will confirm how much you owe, exactly at the current date, 48 hours after you file the amended tax return.


Disclaimer: If you are in any doubt about what you can and cannot claim for, it is important that you contact an accountant or relevant tax specialist who can give you bespoke advice directly relevant to your circumstances.
None of the information given here is tax advice.