Key takeaways
- A Self Assessment return can be amended within 12 months of the filing deadline, so a 2025/26 return can usually be changed until 31 January 2028.
- Online amendments can be made 72 hours after filing, through 'Tax return options' in your Self Assessment account.
- If an amendment increases your tax, interest normally runs from the original due dates for that tax year.
- HMRC does not charge an inaccuracy penalty if you took reasonable care, and can reduce a careless error penalty to nil if you disclose it unprompted.
- After the 12 months, overpaid tax can be claimed in writing as overpayment relief up to 4 years after the end of the tax year.
You can amend a Self Assessment tax return within 12 months of the 31 January filing deadline, so a 2024/25 return can usually be changed until 31 January 2027 and a 2025/26 return until 31 January 2028. Online, wait 72 hours after filing, sign in, go to 'Tax return options' in your Self Assessment account, correct the return and file it again. After the 12 months are up you have to write to HMRC instead.
The steps and time limits below were checked against GOV.UK and HMRC's Self Assessment Claims Manual on 17 September 2026.
Deadline to amend a Self Assessment return
You can correct a tax return within 12 months of the Self Assessment deadline, online or by sending another paper return (GOV.UK). For online returns that means 12 months from 31 January after the end of the tax year:
| Tax year | Online filing deadline | Usually amend by |
|---|---|---|
| 2023/24 | 31 January 2025 | 31 January 2026 (passed) |
| 2024/25 | 31 January 2026 | 31 January 2027 |
| 2025/26 | 31 January 2027 | 31 January 2028 |
If you miss this deadline, or need to change a return from an earlier year, you need to write to HMRC. That route is covered below.
How to amend your tax return online
You must wait 3 days (72 hours) after filing before you can update an online return. Then:
- Sign in to your HMRC online account.
- From 'Your tax account', choose 'Self Assessment account'.
- Choose 'More Self Assessment details'.
- Choose 'At a glance' from the left-hand menu.
- Choose 'Tax return options'.
- Choose the tax year for the return you want to amend.
- Go into the tax return, make the corrections and file it again.
If you filed using commercial software, contact the software provider for help correcting the return, and contact HMRC if the software cannot make corrections. If you are not sure how to sign in, our guide to the HMRC personal tax account may help.
How to amend a paper tax return
- Download the SA100 tax return form, or call HMRC and ask for it. Other forms and supplementary pages can also be downloaded.
- Fill in the pages that need correcting.
- Write 'amendment' on each page and include your name and Unique Taxpayer Reference (UTR). Your UTR is on previous tax returns and HMRC letters, and our guide explains how to find your UTR number.
- Send the corrected pages to the address on your Self Assessment paperwork. If you cannot find it, send them to Self Assessment, HM Revenue and Customs, BX9 1AS.
HMRC will send you an updated bill. It pays any refund directly into your bank account, as long as you include your bank details on your tax return (GOV.UK).
What happens to your bill after an amendment
If you amend online you see your amended bill straight away. Within 3 days your statement also shows the difference from the old one, so you can see whether you owe more or less tax, and any interest. To view it, sign in and choose 'View statements' from the left-hand menu.
- If you owe less: you may be able to claim a refund. See how to get a Self Assessment tax refund.
- If you owe more: the updated bill shows the deadline for paying and the effect on any payments on account you need to make.
Penalties and interest if the amendment increases your tax
When the extra tax is due
Where a self assessment is amended, whether by you or by HMRC, the extra tax is due by the later of the normal due date (usually 31 January after the tax year) or 30 days from the date the notice of amendment is given (HMRC manual SALF304).
Interest from the original due date
Interest on the extra tax normally runs from the original due dates for that tax year, even though the payment deadline for the extra tax itself may be later (HMRC manual SALF305). GOV.UK says the same about returns filed with provisional figures: if more tax is due, interest is worked out from the original due date, and if you overpaid you get interest paid to you (GOV.UK).
HMRC's late payment interest rate is 7.75% from 9 January 2026 and its repayment interest rate is 2.75% from 9 January 2026, according to its interest rates page checked on 17 September 2026. Rates change with the Bank of England base rate.
Penalties for errors
An amendment on its own does not mean a penalty. HMRC may charge a penalty for an inaccuracy that results in tax being unpaid, understated or over-claimed and that was careless or deliberate. It will not charge one if you took reasonable care and the return was still wrong (HMRC factsheet CC/FS7a).
| Behaviour behind the error | Unprompted disclosure | Prompted disclosure |
|---|---|---|
| Reasonable care | No penalty | No penalty |
| Careless | 0% to 30% | 15% to 30% |
| Deliberate | 20% to 70% | 35% to 70% |
| Deliberate and concealed | 30% to 100% | 50% to 100% |
Penalties are a percentage of the extra tax. A disclosure is unprompted if you tell HMRC before you have any reason to believe it has discovered, or is about to discover, the error. If you sent a return you believed was correct and later find a careless inaccuracy, HMRC may reduce the penalty to nil, but only for an unprompted disclosure. Correcting a mistake yourself as soon as you find it is the safest course.
Separate penalties apply if the original return or payment was late. See our guide to the Self Assessment late filing penalty.
If you have missed the deadline to amend
If your return is wrong and it is more than 12 months after the Self Assessment deadline, you need to write to HMRC (GOV.UK).
Reporting income you left out
Write to HMRC with the tax year you are correcting, why you think you have paid too little tax, how much you think you have underpaid, and your signature. HMRC will review the information and contact you if it needs more details.
Claiming overpayment relief for older years
If you paid too much tax, you can claim overpayment relief up to 4 years after the end of the tax year it relates to. Your letter must include:
- that you are making a claim for overpayment relief
- the tax year for which you think you paid too much tax
- why you think you have paid too much tax
- how much you think you have overpaid
- whether or not you have previously made an appeal for the same payment
If any of this is missing, the claim will be rejected. You must also include a declaration that the details are 'correct and complete to the best of your information and belief', signed by you. No one else, including a tax agent, can sign it on your behalf. You can say how you want to be repaid, and you should keep evidence of the overpaid tax, as HMRC may ask for it later (GOV.UK).
| Tax year | Tax year ended | Overpayment relief claim by |
|---|---|---|
| 2022/23 | 5 April 2023 | 5 April 2027 |
| 2023/24 | 5 April 2024 | 5 April 2028 |
| 2024/25 | 5 April 2025 | 5 April 2029 |
Two limits in HMRC's Self Assessment Claims Manual are worth knowing. Overpayment relief is not available while you can still amend the return itself, so for 2024/25 you would normally amend the return before 31 January 2027 instead (SACM12080). The claim cannot be made on the tax return form itself; it must be a separate claim in writing (SACM12150). There are other exclusions too, for example where the tax was calculated in line with the practice generally prevailing at the time (SACM12070). HMRC's refusal of a late claim cannot be appealed (SACM12005).
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