How do I amend a Self Assessment tax return?
You can correct a Self Assessment return within 12 months of the filing deadline, online or on paper, but you must wait 72 hours after filing before you update an online return. After the 12 months, or for an earlier tax year, you write to HMRC instead.
Figures checked against gov.uk on . General information, not tax advice.
At a glance
- Window to change a return
- 12 months after the Self Assessment deadline
- Wait after filing online
- 3 days (72 hours)
- Overpayment relief claim
- Up to 4 years after the end of the tax year
Amending online
Sign in to your HMRC account, choose the Self Assessment account, then More Self Assessment details, At a glance and Tax return options. Select the tax year, make the corrections and file again. gov.uk's example is that a 2024 to 2025 return usually has to be changed by 31 January 2027, which puts a 2025/26 return's window at 31 January 2028.
Amending on paper, or after the window
For a paper return, send the corrected pages with amendment written on each page, plus your name and UTR. Once the 12 months have passed, you write to HMRC: to report income you left out, say the tax year, why you think you underpaid and how much, and sign the letter.
If you think you overpaid, you can claim overpayment relief up to four years after the end of the relevant tax year. gov.uk says the declaration must be signed by you, and a tax agent cannot sign it on your behalf.