Can I Change My Tax Return After Submitting It

Introduction

Submitting a Self Assessment tax return can be complicated, especially if you have multiple income sources or business expenses. Errors happen, but HMRC provides a simple process for making amendments to ensure your tax records are accurate.

Whether you filed your return online or by post, you can usually make changes for up to 12 months after the filing deadline. However, the method and timeframe for corrections depend on how and when you originally filed.

When you can change your tax return

You can amend your tax return if:

You made a mistake or omission when entering income, expenses, or reliefs.

You forgot to claim an allowable expense or tax relief.

You entered incorrect figures or duplicated an entry.

You want to correct your bank details or other administrative information.

You cannot use the amendment process to challenge a formal enquiry or tax investigation already opened by HMRC. In those cases, you must cooperate with HMRC’s enquiry process instead.

How long you have to make changes

You can amend your tax return within 12 months of the normal Self Assessment deadline.

This means:

For the 2023 24 tax year, the filing deadline is 31 January 2025 (for online returns).

You can make amendments until 31 January 2026.

If you filed a paper return, the deadline is earlier — 12 months from 31 October following the end of the tax year.

After this period, you cannot amend your return online, but you may still be able to claim or correct overpaid tax by writing directly to HMRC.

How to amend your tax return

1. If you filed your return online

If you submitted your tax return using HMRC’s online Self Assessment portal:

Log in to your HMRC account.

Go to “Self Assessment” and select “More Self Assessment details.”

Choose “Amend Self Assessment return.”

Make the necessary corrections and resubmit.

HMRC will update your record automatically and send confirmation of the changes.

If you used commercial accounting software, you can log into that system and follow a similar process, ensuring it connects directly to HMRC’s portal.

2. If you filed a paper return

If you filed your tax return on paper, you must:

Download a new copy of the tax return form for the relevant year from GOV.UK.

Write “Amendment” on each corrected page.

Send the revised pages to HMRC by post.

Make sure you include your Unique Taxpayer Reference (UTR) and explain what changes you made.

3. If an accountant submitted your return

If an accountant or tax adviser filed your return, contact them as soon as you spot an error. They can amend the return on your behalf using their agent portal.

What happens after you amend your tax return

Once you make changes, HMRC will:

Recalculate your tax liability.

Update your Self Assessment record.

Send you a revised SA302 tax calculation showing the new figures.

If the correction results in additional tax to pay, you must settle the balance as soon as possible to avoid interest or penalties.

If you have overpaid tax, HMRC will automatically process a refund or adjust your next payment on account.

It can take up to six weeks for amended returns to be reviewed and processed.

What to do if the amendment deadline has passed

If more than 12 months have passed since the filing deadline, you can no longer use the standard amendment route. However, you may still be able to:

Claim overpayment relief: If you have paid too much tax, you can write to HMRC within four years of the end of the tax year to request a refund. You must explain why you believe you overpaid and provide supporting evidence.

Disclose undeclared income: If you failed to declare income and owe additional tax, contact HMRC voluntarily. Making a voluntary disclosure can reduce penalties.

Appeal an assessment: If HMRC issues a tax assessment you believe is incorrect, you can appeal within 30 days of receiving it.

Correcting common mistakes

Typical errors that require amending a tax return include:

Forgetting to declare bank interest or dividends.

Omitting freelance or rental income.

Entering the wrong employment income or PAYE tax paid.

Misreporting pension contributions.

Overstating expenses or claiming ineligible deductions.

Even small mistakes can change your tax liability, so it is worth double-checking all figures carefully before submitting an amendment.

Penalties and interest on amended returns

If your amendment increases your tax bill, HMRC may charge:

Interest on the extra amount due from the original payment deadline.

Penalties if the mistake was careless or deliberate.

If you are reducing your tax bill, HMRC may repay the difference plus interest, provided your claim is valid and within time limits.

To minimise penalties, you should correct any errors as soon as you notice them and provide full explanations where necessary. HMRC takes a more lenient approach when taxpayers act promptly and transparently.

Record keeping

Keep a copy of your amended return and any correspondence with HMRC for at least five years after the filing deadline. You may need these records if HMRC queries your tax position later.

If you use accounting software, ensure it stores a version history of your submissions and amendments for future reference.

Example scenario

Sophie, a self-employed solicitor, filed her 2022 23 tax return online in January 2024 but later realised she forgot to include £2,000 of professional expenses. She logged into her HMRC account in March 2024, amended the return, and reduced her tax bill by £400. HMRC confirmed the update and refunded the difference within four weeks.

By acting quickly, Sophie avoided penalties and ensured her records were accurate before the 2025 filing season.

Common mistakes to avoid

Waiting too long to correct an error.

Forgetting to resubmit the amended return after editing.

Not explaining the reason for changes if requested by HMRC.

Ignoring additional tax due after the amendment.

Failing to keep supporting documentation for future reference.

Conclusion

You can change your tax return after submitting it, but only within 12 months of the Self Assessment deadline. Amending online is usually the quickest method, and HMRC will automatically update your records and adjust your tax bill.

If you miss the amendment window, you can still request overpayment relief or make a voluntary disclosure. Acting quickly and keeping detailed records will help ensure your tax affairs remain accurate and compliant.

If your situation is complex or you are unsure how to amend your return, consult a qualified accountant or tax adviser to avoid further errors or penalties.