Can I Make Changes to My Tax Return?

We all make mistakes, and in most scenarios we can just brush them off and get on with our day. But some mistakes, like errors on your tax return, feel like the end of the world.

First things first! Take a deep breath – it is fixable. How you proceed depends on how long it’s been since you submitted your return. Whether it’s your Self Assessment or a Company Tax Return, we’ll guide you through how to make amends.

Why would I need to amend my Self Assessment?

There are different reasons why you might need to amend your Self Assessment, ranging from a few typos to forgetting to add an invoice, or even admin errors. What’s important is that you fix any known issues, rather than hoping that they go away.

How long do I have to amend my Self Assessment?

You can make amendments to your tax return within 12 months of your Self Assessment deadline.

For example

The Self Assessment deadline for online submissions covering the 2024/25 tax year is 31st January 2026. If you need to make any amends, you have until 31st January 2027 to do so.

You can make amends to your Self Assessment after this point, but you’ll need to write to HMRC in order to do so.

How do I amend my Self Assessment?

Amending your Self Assessment tax return is fairly straightforward if you do it within the 12-month window. If you’ve realised pretty early on from the submission deadline you’ve made a mistake, you’ll need to wait 72 hours before you’re able to make any changes. Once you have access to amend your return:

Sign into your tax account
Go to ‘Self Assessment account’
Proceed to ‘More Self Assessment details’
Click ‘At a glance’ (this should be in the left-hand menu)
Then go to ‘tax return options’
Choose the tax year you need to amend
Go into that tax return, make the amendments, double-check it and then file it again

You might not have an accountant, but if you do, let them know first before you make any changes!

Your tax bill might change if you’re updating invoices or adding in untaxed income. Things like a change of address or name won’t usually alter your bill.

Amending your Self Assessment after 12 months

You can still make changes to a previous Self Assessment tax return after the 12 month period has passed. It does mean writing a letter to HMRC though, which can be daunting. It’s important that your letter be as specific as possible, so include:

Exactly which Self Assessment tax year you’re referring to
The error that needs correcting
Why you believe you’ve over or underpaid in tax, and how much you believe you have over or underpaid

Ensure you sign the letter with your signature and send it to:

Self Assessment
HM Revenue and Customs
BX9 1AS
United Kingdom

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Why would I need to amend a Company Tax return?

This could be a mistake or typo you’ve made on your actual tax return, or on any supporting documents you’ve attached with it. For instance, you need to update the figures on your profit and loss balance sheet.

It may be appealing to bury your head in the sand and hope HMRC miss it, but it’s much better amend mistakes as soon as possible – it will certainly help minimise any penalties!

How long do I have to amend my Company Tax Return?

You have 12 months from your filing deadline to make any amends. This gives you 2 years to file the necessary amendments from the end of the accounting period covered by your return.

If you’ve realised there’s been an error past this point, you need to inform HMRC anyway, otherwise you could incur penalties if HMRC do a check.

Read our guide to Company Tax Returns

How do I amend my Company Tax Return?

If you’re within 12 months of the filing deadline you can make your amendments by:

Using commercial software
Using HMRC’s free online filing service (if this is how you sent your return)
Sending a paper return or writing to the Corporation Tax office

Amending your Company Tax Return more than 12 months after the filing deadline

If the 12 month amendment period has passed, then you’ll need to post the filing to HMRC. Any digital submission after this point will be rejected. Once you’ve downloaded and printed the relevant filings, you’ll need to post it to:

Corporation Tax Services
HM Revenue and Customs
BX9 1AX
United Kingdom

This can be tricky to do, so make sure you have a chat with your accountant first!

Need help with your tax returns? Learn more about our online accounting services for businesses. Call 020 3355 4047 to chat to the team, and get an instant online quote.