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Can I amend my Self Assessment after submitting?

  • 3 min read
  • Last updated 18 May 2023

You’ve submitted your Self Assessment tax return already and life is good… until you realise you’ve made a mistake and need to change something 😱

Not to worry, here’s how you can amend your tax return👇

Why would you need to make an amendment to your Self Assessment? 

Amending your tax return can result in you receiving a tax refund or owing HMRC more in tax.

If you do need to make any amendments, you have to wait at least 3 days from when you filed to do so.

Some reasons you might need to amend your tax return could be that you:

  • Forgot to add something (like untaxed income)
  • Changed your name or address within the same year
  • Spelt something wrong 
  • Noticed any mistake (even if it’s a small one)
  • Want to claim overpayment relief

Since you’re trying to correct the mistake before HMRC contacts you about it, you might be able to avoid penalties for an incorrect tax return🤞

First, you need to figure out how long it’s been since the filing deadline for the tax return you want to amend.  That’s 31st January, in case you’ve wiped it from your memory already (we wouldn’t blame you)🥲


If you filed your 2021/2022 tax return by 31st January 2023, you have until 31st January 2024 to make an amendment online.

If your year is up, then you have to request the amendment a different way.

Amending within 12 months of the Self Assessment deadline

You can amend your Self Assessment without too much fuss if it’s been less than 12 months since the deadline🎉


If you filed through HMRC, you can log into your tax account

Click on:

  1. “Self Assessment account”
  2. “More Self Assessment details”
  3. “At a glance”, on the left
  4. “Tax return options”
  5. The tax year you want to make amends for 
  6. The tax return you’re amending

Make the changes to your online tax return and file it again. 

With TaxScouts

If you’re with TaxScouts, it’s simple. Just log in, let your accountant know and they’ll handle everything. Easy, as usual🤩

Amending more than 12 months from the Self Assessment deadline

If you need to make an amendment to a tax return that was filed over a year ago, the process is a little different.

Regardless of who filed your tax return for you, you’ll need to send your amendments to HMRC in writing yourself. That’s right, good old post😨


Self Assessment

HM Revenue and Customs


United Kingdom

There’s a different address for couriers.

You can claim a tax refund from up to 4 years after the year the tax return was filed for. But fair warning, HMRC does have the right to reject any amendments made after the 12-month deadline (even if they were made by paper).

How do you write to HMRC to amend your tax return?

This is the only option if you:

  1. Filed a paper return originally and need to make an amendment
  2. Need to make an amendment and it’s been more than 12 months since the deadline

HMRC is specific in what they need you to include in the letter including:

  • The tax year that needs amending 
  • A reason why you think you underpaid or overpaid tax
  • How much you think you’ve over/underpaid 
  • Your signature

If you’re making a claim, HMRC ask that you include the following:

  • Confirmation you’re making a claim because you’ve overpaid tax
  • Proof that you paid the tax already through Self Assessment for the year you’re amending (like a submission receipt)
  • How you want to be paid back (bank account, cheque, etc)
  • Confirmation that you haven’t tried to claim this refund before
  • Your signed declaration to confirm that everything you’ve said is correct to your knowledge

Will there be any changes to your tax bill?

Yep, more than likely if you know there was a mistake, your tax bill will change.


 If you amended it online with HMRC, then your bill is changed straight away. Within 3 days you should be able to see if you owe more tax or are owed a refund.

If you owe tax, you’ll see the new deadline to pay your new tax bill by, any payments on account you need to make, and if you owe HMRC any penalty interest fees.

On the other hand, if you’re owed money, click on “Request repayment” on your HMRC online account. 

It usually takes about 4 weeks for the refund to reach your account. 


HMRC will send you an updated bill within 4 weeks with more instructions on what to do. As long as you’ve included your bank details in your amended tax return, they’ll send any owed money directly to your bank account. 

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