Self Assessment tax returns

6. If you need to change your return

You can make a change to your tax return after you’ve filed it, for example because you made a mistake. You’ll need to make your changes by:

  • 31 January 2018 for the 2015 to 2016 tax year
  • 31 January 2019 for the 2016 to 2017 tax year

If you miss the deadline or if you need to make a change to your return for any other tax year you’ll need to write to HMRC.

Your bill will be updated based on what you report. You may have to pay more tax or be able to claim a refund.

Updating your tax return

How you update your tax return depends on how you filed it.

Online tax returns

  1. Log in to your HMRC online account.

  2. From ‘Your tax account’, choose ’Self Assessment account’ (if you don’t see this, skip this step).

  3. Choose ‘More Self Assessment details’.

  4. Choose ‘At a glance’ from the left-hand menu.

  5. Choose ‘Tax return options’.

  6. Choose the tax year for the return you want to amend.

  7. Go into the tax return, make the corrections and file it again.

Paper tax returns

Download a new tax return, and send HMRC the corrected pages. Write ‘amendment’ on each page, and include your name and Unique Taxpayer Reference (UTR) - this is on previous tax returns or letters from HMRC.

Check your Self Assessment paperwork for the address. If you can’t find this, send your corrections to the address for general Self Assessment enquiries.

If you used commercial software

Contact the software provider for help correcting your tax return. Contact HMRC if your software isn’t able to make corrections.

Write to HMRC

Write to HMRC if you need to make a change to your tax return from the 2014 to 2015 tax year or earlier.

Include in your letter:

  • the tax year you’re correcting
  • why you think you’ve paid too much or little tax
  • how much you think you’ve over or underpaid

You can claim a refund up to 4 years after the end of the tax year it relates to. If you’re making a claim, also include in your letter:

  • that you’re making a claim for ‘overpayment relief’
  • proof that you’d paid tax through Self Assessment for the relevant period
  • how you want to be repaid
  • that you haven’t previously tried to claim back this refund
  • a signed declaration saying that the details you’ve given are correct and complete to the best of your knowledge

Changes to your bill

You’ll see your amended bill straight away if you updated your tax return online. Within 3 days, your statement will also show:

  • the difference from the old one, so you can see whether you owe more or less tax
  • any interest

To view this, log in to your account and choose ‘View statements’ from the left-hand menu.

If you’re owed tax

To claim a refund, go to ‘Request a repayment’ from the left-hand menu within your HMRC online account. Allow 4 weeks for your refund to be sent to your bank account.

You may not get a refund if you have tax due in the next 35 days (for example for a payment on account). Instead, the money will be deducted from the tax you owe.

If you need to pay more tax

Your updated bill will also show:

If you sent an updated paper return

HMRC will send you an updated bill within 4 weeks. They’ll also pay any refund directly into your bank account, as long as you included your bank details on tax return.