How do I amend my tax return after it has been submitted?

After submitting your tax return, you may realise that it needs amending. This could be due to a mistake or the realisation that you may not have claimed all allowable expenses! Regardless of the reason, as soon as the problem is identified, it should be actioned upon as soon as possible.

For the 2018 to 2019 tax year, you’ll need to make your changes by 31st January 2021. There are different ways to amend your tax return, this depends on how it was filed i.e. online, using commercial software or by paper.


If you filed your tax return online, you will need to log into your Government Gateway account to make the changes. Navigating your way through your Government Gateway account can sometimes be a bit tricky, therefore follow the steps below and you’ll be able to get to where you need to go:

  • Select “More Self-Assessment details
  • Select “At a glance”
  • Select “Tax Return Options”
  • Select the required tax year for amending
  • Make all necessary amendment
  • File the return

Your amended bill will be visible immediately after submitting your amended return. After 3 days, you will also be able to see your statement which will show the difference from your old statement and any interest. If you end up owing more tax, you will be given a deadline to pay the outstanding amount. You can claim any Self-Assessment refund directly from your Government Gateway account, this can take up to 4 weeks to reach your bank account.

Commercial Software

Commercial software packages can be different, therefore you will need to contact the provider to see how to correct a tax return. If you are not able to make amendments through your software, contact your accountant or HMRC. You will be able to see any tax owed or owing on your Government Gateway account or HMRC will send you a letter showing your statement.

By paper

If you send your return in by paper, then all you are required to do is download a new tax return and send HMRC the amended pages. Be sure on each page to write ‘amendment’ as well as your name and your Unique Taxpayer Reference number. You can find the address to send your paper tax return here. You will receive your updated bill within 4 weeks of HMRC receiving your amended tax return, this will notify you of any bill or refund. If you have included your bank details in your return, any refund will be paid directly into your bank account.

Missing the deadline or correcting a previous year

If you miss this deadline or notice that a previous tax year needs amending then you will have to contact HMRC by written communication. In your letter, you will need to include:

  • The tax year that you are amending
  • The reason why you think that you have paid too much or not enough tax
  • How much you think you have overpaid or underpaid

If you believe that you are eligible for a refund due to overpaying, then you can claim a refund up to four years after the end of the relevant tax year. If you are claiming a refund, in your letter you must also include:

  • That you are claiming “overpayment relief“
  • Proof that you have already paid tax for the tax year you are currently amending
  • How you would like the refund to be paid
  • That this refund has not previously been claimed
  • A signed declaration stating that the details are “correct and complete to the best of your knowledge”