Amended Self Assessment Returns: How to Correct Mistakes
Mistakes happen. Perhaps you forgot an income source, miscategorised an expense, or entered the wrong figure. The good news is that HMRC allows you to amend your Self Assessment return.
When Can You Amend?
You can amend your return within 12 months of the original filing deadline. For a 2026/27 return (deadline 31 January 2028), you can amend until 31 January 2029.
How to Amend Online
- Log in to your Government Gateway account
- Go to your Self Assessment section
- Select the return you want to amend
- Make the necessary changes
- Resubmit the return
HMRC will recalculate your tax. If you owe more, you need to pay the difference plus any interest. If you have overpaid, you will receive a refund.
After the Amendment Window
If you need to correct an error after the 12-month amendment window, you need to write to HMRC and explain the error. They have the discretion to allow corrections outside the normal window.
Voluntary Disclosure
If you have deliberately underreported income or overclaimed expenses, making a voluntary disclosure before HMRC discovers the error typically results in lower penalties. HMRC treats voluntary corrections more favourably than errors they discover themselves.
Prevention
The best way to avoid amendments is to get it right the first time. Accounted keeps accurate records throughout the year, reducing the chance of errors when you file.
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Tax & Compliance Specialists
Our tax specialists have decades of combined experience in UK sole trader and small business taxation, MTD compliance, and HMRC submissions. All content is reviewed against current HMRC guidance before publication and updated quarterly to reflect legislative changes.
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