Amending a tax return

When to amend a tax return

If you realise you have made a mistake on your tax return, you should amend it as soon as possible to correct the error. 

If you used provisional figures when you originally completed your tax return because you were missing some information, you should amend the tax return to replace the provisional figure with the actual figure as soon as the relevant information becomes available. 

In particular, if you are self-employed or in a partnership and have an accounting date that falls between 6 April and 30 March (inclusive), following the ‘basis period reform’ changes which were made in tax year 2023/24, you may need to amend your 2024/25 tax return. This will be the case if you used an estimated amount when calculating your taxable profits figure for your 2024/25 tax return because your self-employment or partnership accounts had not been finalised when you were completing your return. 

You should amend your tax return by replacing the estimated figure you used in your calculation of taxable profits (being the provisional figure) with the actual figure once the accounts for the relevant period have been completed and you can then work out the correct amount.

You will need to bear in mind the time limit for making the amendment as explained in the Deadlines section below. 

If additional tax becomes due as a consequence of the amendment then this should be paid as soon as possible. In this case, if you are required to make payments on account for the next tax year they will also increase as a result of the amendment, and should also be paid as soon as possible. Interest will be charged from the original due date for the tax until the date of payment. If you have overpaid tax you should receive a refund once the amendment has been processed. 

We explain below what the deadline is for amending a return and what to do if you miss the deadline.

You can amend your return any number of times before the amendment deadline.

Deadline

You have up to 12 months from 31 January following the end of the tax year to which the tax return relates to make the amendments. If the notice to file the return was issued after 31 October, you can amend the tax return within 15 months of that notice being issued.

Therefore, if you need to amend your 2024/25 tax return and submitted it to HMRC by 31 January 2026, you will normally have until 31 January 2027 to make the amendment. This applies regardless of whether you filed a paper return or you filed online. 

If, for example, you did not receive a notice requiring you to file your tax return for 2024/25 until 12 December 2025, then you can amend it up until 11 March 2027.

If you have missed the deadline

If you need to amend your tax return outside of the above time limits, HMRC say you should write to them to explain what has happened. The information you need to include in your letter is set out on GOV.UK. You may wish to get help depending on the circumstances. 

If additional tax is due as a result of the amendment, HMRC will let you know what you need to do to bring your tax affairs up to date. This may involve making a formal voluntary disclosure to HMRC.

If tax has been overpaid, you may be able to make a claim for overpayment relief to obtain a refund. You can read about how to do this on our page Self assessment tax refunds.

How to make an amendment

If you filed your original tax return online, you can make the amendment online through HMRC’s self assessment portal. You can also make the amendment on paper by writing to HMRC.

If you used third party software to file the return originally, you should use this to make the amendment.  

Paper filers should make any amendments on paper. For more information, see GOV.UK.