How to amend a Self Assessment tax return that you’ve already filed

It can happen to the best of us. You file your Self Assessment tax return to HMRC before the deadline and then realise that you made a mistake on one of the forms. Luckily, HMRC has devised a simple process to help you correct errors on a tax return that you’ve already filed.

We strongly recommend that you check with HMRC or an accountant before making any changes to a filed tax return.

How to correct an error if you filed your tax return using HMRC’s portal

If you filed online

If you filed your tax return using HMRC’s online portal, you can correct the error by signing in to the portal with your Government Gateway user ID and password and navigating to 'Your tax account'.

From there, navigate to 'Self Assessment account' and then 'More Self Assessment details' > 'At a glance' > 'Tax return options'.

Choose the tax year of the Self Assessment tax return that you want to edit. Make the necessary corrections to the tax return and then file it again.

If you filed using pen and paper

If you filed your tax return to HMRC using pen and paper, you’ll need to print a new tax return form and mark the corrections clearly, using the instructions on HMRC’s website. You should then send the corrected tax return to HMRC in the post.

How to correct an error if you filed your tax return using FreeAgent

If you filed your tax return using FreeAgent and find that you need to create or amend any transactions, please speak to an accountant first.

Once your accountant has advised whether you should make any corrections, you can unlock the tax return in FreeAgent, make the changes in line with HMRC’s guidance and then re-file your amended tax return to HMRC from FreeAgent. Your accountant can also do this on your behalf.

Alternatively, your accountant might recommend that you make adjustments to account for the errors in the following tax year.

How soon can you amend a mistake in a filed tax return?

You can tackle an error on a filed tax return as soon as you notice it. There is, however, a deadline for correcting any mistakes: one year after the online filing deadline of the tax return that you want to correct.

If you made a mistake on your 2021/2022 tax return after you filed it to HMRC, for example, your deadline for correcting any mistakes would be 31st January 2024, one year after the online filing deadline of 31st January 2023. If you miss this deadline, you can still contact HMRC directly to explain the error.