How to amend your self-assessment tax return

Filing your own taxes is a big job, and mistakes on tax returns can be frustrating. You may get everything done on time, or even early, only to realise something on the return was incorrect.

The good news is that HMRC provides an amendment grace period. Whether you think you’ve overpaid or still owe for a return you’ve already submitted, there’s a simple process in place for setting things right. 

In this article, we’ll talk about why you might need to amend a return you’ve already filed. We’ll share everything you need to know about reporting oversights by filing an amendment to your return. We’ll also make sure you know how to claim your amended refund or pay any additional tax due.

Top Tip: Filling out your own tax return can seem daunting. But there’s no need to worry if you know how to prepare. Learn everything you need to know to complete your return in our guide to Self Assessment tax returns 🔎

Table of contents

What is a tax return, and how do I file one?

Before diving into the details (deadlines, figures and penalties), let’s talk about what an income tax return is and why you might need to submit one.

Taxes are generally withheld automatically from wages, savings and pensions. However, if you’re self-employed or have another source of income outside the PAYE scheme (where an employer deducts taxes and National Insurance payments from your pay), you’ll need to report and pay annual income taxes to HMRC yourself. You do this through a Self Assessment tax return.  

You are required to pay Self Assessment tax if you’re: 

  • Self-employed as a sole trader or
  • A partner in a business partnership 

You may also need to complete a return if you have income outside of regular wages and pensions, including: 

If you fall into any of these categories, you must register for Self Assessment. The deadline for registering is 5th October before the end of the tax year in which you began trading. Once registered, you must fill out a return and file it with HMRC either online, by mailing a paper return or through third-party tax software. 

For more information about Self Assessment tax returns, or to get help filling one out, visit GOV.UK.

Top Tip: Hiring an accountant can help keep your finances in good shape. Learn how to find the right help for your small business in our guide to choosing an accountant 📌

Why you might need to amend your tax return

Once you’ve submitted your return, you’re all set with taxes for the year. Unless you find you made an error or need to make a correction, or HMRC finds something amiss in the information you submitted.

Mistakes on tax returns can result in penalties depending on the type of error incurred. But not to fear. HMRC has provided an option for amending returns that lets you act to make corrections when you discover a problem.

Both the taxpayer filing and HMRC have the right to make corrections to a tax return. Either party might amend a return because of incorrect figures or inaccuracies. Here are the types of modifications each is responsible for.

HMRC corrections

HMRC will make amendments to fix any obvious discrepancies in a return. They can make adjustments to reverse or eliminate errors that might stall a taxpayer’s return. These are usually errors in arithmetic or simple technicalities. For instance, HMRC might make amendments if earning amounts were entered correctly but the total sum is off. 

HMRC will notify you of any proposed changes to your original return and get approval before proceeding. You then have a limited window to accept or reject the proposal. If you reject it and HMRC disagrees with you, they can open an enquiry. 

Learn more about what happens when HMRC sends an amended tax return at GOV.UK

Taxpayer amendments

The taxpayer also has the right to amend a return that’s already been filed. You don’t have to wait for HMRC to discover the problem and potentially face penalties for incorrect filing. Instead, you can proactively make the change. 

You might adjust the information if you find you:

  • Need to update personal information with HMRC
  • Entered the wrong figures
  • Think you paid too much
  • Think you paid too little

Filing an amendment allows you to make up for underpayment before it can result in a penalty. It also lets you reclaim money if you’ve overpaid your taxes for a given year. The key is to keep good track of your financial information and take action within the allotted time frame. 

Top Tip: Keeping good records is crucial to staying on top of your taxes when you’re running a small business. You need to know what information to record and report. Start by learning all about what taxes you are accountable for in our complete guide to small business tax 🎯

When you can amend a return

There are set time frames when you (or HMRC) can update your return. If you fail to address any issues within this period, you may still be able to make corrections. But you’ll have to write to HMRC directly to discuss it. Here are the dates you need to know. 

When the taxpayer can amend a return

You must wait for at least 72 hours after you’ve filed your return before you can make any changes to it. Once that period has passed, you have one year after the tax return deadline to file an amendment. So for the most recent tax years, the filing deadlines are:

  • 31st January 2022 (for the 2019-2020 tax year)
  • 31st January 2023 (for the 2020-2021 tax year)

If you miss these time limits or want to make changes for any other tax year, you must contact HMRC in writing. 

For more information on deadlines for submitting an amended tax return, visit GOV.UK.

When HMRC can amend a return

HMRC can make changes to a tax return for up to nine months after it’s been submitted. The agency will notify you of the changes they propose, and you then have the opportunity to accept or reject the changes. 

If you disagree with what they propose, you may appeal the proposed changes within 30 days of when HMRC issued the notice. 

Learn more about how HMRC can submit corrections to your tax return at GOV.UK.

What if I miss the deadline?

If you miss the deadline for filing an amendment for your most recent return, or if you want to amend a return from a previous year, you’ll need to reach out to HMRC by mail and make the request. You can still request to make changes for four years from the end of a given tax year. 

So, for example, the 2018-2019 tax year ended on 5th April 2019. If you find you need to change information on the return for that year, you have until 5th April 2023 to do so.

When you contact HMRC about a change, be sure to include the following information:

  • The tax year for the return you wish to amend
  • An explanation of the change you’re requesting
  • The amount you believe you’ve over or underpaid

If you’re claiming overpayment and requesting a tax refund, you’ll also need to include:

  • A statement that you’re claiming ‘overpayment relief’
  • Documentation of your Self Assessment tax paid for the relevant period
  • How you would prefer to receive payment
  • A statement that you haven’t already tried to claim this refund
  • Your signature, indicating that the information you’ve included is correct and complete to the best of your knowledge

For additional information on how to file an amendment for any tax years for which the deadline has passed, visit GOV.UK

How to amend a tax return

How you amend your return depends on how you filed it in the first place. As mentioned, you currently have three options for filing: filling out online returns, using third-party software, or submitting paper tax forms by post. 

You must use commercial software or paper tax forms to file a return if you:

  • Are part of a business partnership
  • Are filing for a trust or estate
  • Get income from a trust
  • Lived abroad 
  • Are an underwriter for Lloyd’s
  • Are a religious minister
  • Wish to report profits from selling more than one asset (‘chargeable gains’)

Here are the steps for completing each of your tax return options.

1. Online return

You can file an online tax return if you’re self-employed or need to send a return because of income you make outside PAYE. Once you’re registered, simply sign in to your online tax account at GOV.UK and fill out the return by the deadline. 

2. Paper return

You can file your returns by post. You just need to download the forms from GOV.UK, print them out and send them in by the deadline.

3. Return filed via third party software

Third-party software can help guide you through filling out your tax return. Some programs can even track your records throughout the year so you have a clear idea of what your return will look like as you go. Third-party software often offers you the chance to talk with an accountant who can review your return for accuracy before you file. HMRC has provided a list of approved commercial software suppliers on their website for your convenience. 

Please note that by the start of the 2024-2025 tax year, self-employed individuals and landlords making over £10,000 will need to comply with HMRC’s Making Tax Digital for Income Tax initiative. So if you haven’t already, now is a good time to get familiar with filing online. 

Top Tip: Making Tax Digital (MTD) is a plan HMRC put in place to make filing taxes more efficient and reduce errors. Learn everything you need to know about MTD as a small business in our guide to Making Tax Digital 🌎

How to claim a refund 

How you claim the money you’re owed depends on how you submitted your amendment. 

Online amendment. Once your return has been filed, you’ll be able to see the changes to your tax bill immediately. And within three days, you’ll be able to see the difference from your original return indicating what you owe or are owed. 

HMRC will not automatically issue a tax refund even if your tax bill shows you overpaid. You’ll have to request it from them. You can claim your refund through your HMRC online account. Simply choose “request payment” from the menu on the left. Alternatively, you can call to request repayment.

Paper amendment. If you sent an updated paper return, HMRC will send you an updated tax bill within four weeks. If you included your bank details on your tax return, they’ll pay your refund directly into your account. Otherwise, you may receive it through the post. 

For more about claiming a refund, visit GOV.UK.

What if I owe more tax?

If you’ve underpaid, a new total will show up in your account once you’ve filed the amendment. It will inform you of the due date for payment as well as how to pay. As with refunds, you can see the changes to your bill in your online account if you filed through the site. Otherwise, you’ll receive a new bill through the mail. 

Learn more about how to pay your Self Assessment tax bill at GOV.UK.

Wrapping up

Resolving any issues with errors on your filed tax return is important. But it doesn’t need to be stressful. As long as you follow proper procedures, HMRC offers a straightforward process to help you get sorted and correct records as quickly as possible. 

Make tracking your financial transactions easier by signing up for a free business bank account today. Used alongside our simple and secure accounting software, you can spend less time on accounting and cut down on the potential for errors in your records.

Photo by Polina Tankilevitch, published on Pexels

Adelaide Carleton

Adelaide Carleton

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