You can amend a Self Assessment return within 12 months of the 31 January filing deadline, so a 2024 to 2025 return can usually be amended until 31 January 2027. After that, you have to write to HMRC, and if you overpaid you can claim overpayment relief up to 4 years after the end of the tax year. Amending a return also gives HMRC a new window to open an enquiry into the amendment.

How long do I have to amend a tax return?

GOV.UK says you can make a change to your return within 12 months of the Self Assessment deadline. For the 2024 to 2025 tax year, with a deadline of 31 January 2026, that means by 31 January 2027. You can amend online if you filed online, or by post for paper returns.

What if the 12 months have passed?

  • If you paid too little, write to HMRC with the correction. Telling HMRC before it contacts you usually means lower penalties.
  • If you paid too much, you can claim overpayment relief within 4 years of the end of the tax year, under Schedule 1AB to the Taxes Management Act 1970.

Can HMRC enquire into an amended return?

Yes. Under section 9A of the Taxes Management Act 1970, HMRC can open an enquiry into an amendment up to the quarter day after the first anniversary of the date the amendment was made. The quarter days are 31 January, 30 April, 31 July and 31 October. So a late amendment can extend the period during which HMRC can ask questions about that change.

Should I amend or wait for HMRC?

If you know a return is wrong, correcting it yourself is almost always better. For errors that increase tax, an unprompted correction can reduce a careless penalty to nothing, compared with a minimum of 15% once HMRC has prompted you. See HMRC penalties for tax return errors. If HMRC has sent a nudge letter, take advice on how to respond.

What about Company Tax Returns and VAT?

Companies can amend a Company Tax Return within 12 months of the filing date. VAT errors have their own rules; see correcting VAT errors.

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Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 7 October 2026. Sources: GOV.UK, Self Assessment tax returns: corrections; Taxes Management Act 1970 section 9A and Schedule 1AB. This guide is general information, not personalised tax advice.