How to Amend Your Tax Return

Have you made a mistake on your self-assessment tax return? Don’t panic, you can go back and correct your tax return after you have filed it with HMRC. In this guide, you’ll find out how to amend your tax return (whatever the reason) and how long you have to make your changes.

Updated 5 October 2021

Friendly Disclaimer: Whilst I am an accountant, I’m not your accountant. The information in this article is legally correct but it is for guidance and information purposes only. Everyone’s situation is different and unique so you’ll need to use your own best judgement when applying the advice that I give to your situation. If you are unsure or have a question be sure to contact a qualified professional because mistakes can result in penalties.

1. How to Amend Your Tax Return Online

HMRC lets you amend your SA100 tax return by going online. You’ll need to log into your .GOV tax account using your HMRC user ID and once inside look in the self-assessment section. There, you should find an option to amend the tax return you previously filed. Alternatively, you can navigate to the tax return you want to correct and select ‘Tax Return Options’ from the menu on the right-hand side you will then be presented with the option ‘Amend Return’.

How to Amend Your Tax Return

2. How Long Do You Have to Correct Your Return?

You have up to 12 months after the filing deadline to fix mistakes in the tax return you have filed. So, if you want to correct your 2019/2020 tax return which was due on 31 January 2021, you’ll have until 31 January 2022 to correct any errors.

3. Correcting a Paper Tax Return

If you fill in a paper tax return, minor mistakes can be corrected over the phone. But, if you have made a more major mistake or need to fill out an additional section, then you’ll need to download blank versions of the required pages from the HMRC website and post them back to HMRC. Alternatively, you can write a letter to HMRC with details of the corrections required and they’ll update your return on your behalf.


Taxes are changing! From April 2024 sole traders will need to report their earnings and pay tax on a quarterly basis. This is known as Making Tax Digital, which you can read more about in this guide to help you get prepared.

About Anita Forrest

Anita Forrest is a Chartered Accountant, spreadsheet geek, money nerd and creator of - a website full of templates, guides and resources for UK sole traders. No faff. No confusion. Just simple straightforward advice on business registration, taxes and bookkeeping.