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ARTICLE · 10 JULY 2025

Need To Know: Amending Self-assessment Tax Returns

Macfarlanes LLP
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If you realise you have made a mistake on your tax return you can amend it within 12 months of the normal filing deadline. This is 31 October for a paper return or 31 January for an online return.

United KingdomTax
Gideon Sanitt
Gideon Sanitt
Sophie Rhind
Sophie Rhind
Isabelle Proctor
Isabelle Proctor

Navigating tax disputes can be a complex and daunting process. This "need to know" series sheds light on the essential elements. In this note, we cover how to amend your tax return, HMRC's powers to amend your tax return, and the risk of penalties.

How to amend your tax return

Within 12 months

If you realise you have made a mistake on your tax return you can amend it within 12 months of the normal filing deadline. This is 31 October for a paper return or 31 January for an online return.

If the mistake results in an increase in tax, you will also need to pay accrued interest. If it lowers the tax, you can claim a refund.

The process for amending your tax return depends on whether you filed it online or filed a paper return:

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