Filing your self-assessment tax return is a significant task to complete. However, sometimes, mistakes can arise. You may forget to state something, you may change your address in the same year but forget to change it, or you may even make a typo. In this case, you need to amend a self-assessment tax return. Here, we have gathered the essentials you need to follow in 2025.
Why Might You Need to Change Your Self-Assessment?
In the UK, you might need to change your Self Assessment tax return for several reasons. HMRC allows you to make amendments if you realise you made a mistake, omission, or if your situation has changed.
Here are the most common reasons:
- You forgot to include some income
- You claimed the wrong expenses or omitted allowable deductions.
- You entered figures incorrectly (e.g., a typo in your income or tax paid)
- You received additional income after submitting the return (e.g., bonuses, late invoices).
- A change in business profits/losses.
- You discovered a loss you could carry forward or back.
- You claimed too much or too little in pension contributions, gift aid, marriage allowances, or capital gains.
- You forgot to report property rental income or capital gains from selling assets.
- You submitted your return in a rush and later spotted errors.
- HMRC contacted you about a discrepancy.
How Long to Amend Self-Assessment Tax Return?
Following the reasons why you need to amend your self-assessment return, it is time to move on to how long you can submit your amended tax return.
You can normally amend a submitted tax return up to 12 months after 31 January following the end of the tax year. For example, you have a deadline until 31 January 2026 to make changes to the 2023-2024 previous tax returns.
Nevertheless, if you feel like you are going to miss the deadline, you can write to HMRC. You can handle tax returns online or by submitting a paper return.
How to Amend Online Tax Returns
The process to amend your online tax return is as simple as filling out your self-assessment. Here are the steps you need to follow:
- First, you need to sign in to your HMRC tax account.
- After you sign up, click on the “Your tax account” and from there “Self Assessment account”
- Once the page is opened, you will see “More Self Assessment details” below.
- From the left-hand menu, you need to choose “At a glance”.
- Then, you will see “Tax return options”. By clicking here, you can choose which tax year you want to make amendments. to
- Lastly, go to the tax return and make the necessary changes. After you make your amendments, you just need to resubmit them.
At this process, it is best to remind that if you are working with an accountant, you can just let them know what corrections need to be done.
How to Make Changes in A Paper Tax Return?
To amend your previous tax return on paper, you need to first download the SA100 tax return form. If you cannot find the form online, then you can contact HMRC and ask them for the SA100 tax return form.
Once you complete or correct the mistakes, you need to send them to the same address on your Self Assessment paperwork. Here, the important thing is that you need to write “amendment” and your name on each page. Plus, you need to write Unique Taxpayer Reference (UTR), which is a 10-digit number issued by HMRC.
At this stage, you may not find the exact address. If so, it is advised to send it here:
Self Assessment
HM Revenue and Customs
BX9 1A
What Happens to Your Tax Bill After You Change Your Self-Assessment Return?
After you make the necessary corrections either online or on paper, you might wonder what is the next step. Well, there are a few scenarios that can happen depending on your corrected tax return.
If it is something like a typo mistake or address change, you will not experience any difference in your tax bill. If you have paid too much tax due to a certain mistake, you can claim a tax refund from HMRC. On the other hand, if you owe more tax, HMRC will update your tax bill. This updated bill will include the new deadline and any changes to your payments on account. At this step, if you send a paper tax return, HMRC will let you get a new and updated tax bill.
In case of a missing deadline, you can still correct your self-assessment tax return by writing to HMRC, especially if it has been more than 12 months since the original deadline. This applies if you need to report missed income, fix an earlier tax year, or claim a tax refund through overpayment relief. Note that you can request up to 4 years after the end of the relevant tax year.
Your letter must clearly state the tax year you are correcting, explain why the correction is needed, how much tax you believe was over- or underpaid, and include your signature. If you claim overpayment relief, you need to mention this specifically. At this stage, you can state whether you have appealed before, and add a signed declaration confirming the details are “correct and complete to the best of your information and belief.” Plus, you need to be sure to provide proof of tax paid, as HMRC may request supporting evidence.
FAQs on Amending a Self-Assessment Tax Return
Does amending a tax return trigger an investigation?
Amending a tax return doesn’t automatically lead to an investigation, but HMRC may ask for more information as part of their routine checks. This is a standard part of their due diligence process to ensure everything is accurate and above board.
How many times can I resubmit a tax return?
You can resubmit or amend your self-assessment tax return as many times as needed within 12 months of the filing deadline.
Can I unsend my tax return?
No, you cannot unsend or withdraw your Self Assessment tax return once it’s been submitted to HMRC. However, you can make changes to correct the mistakes.
