6. If you made a mistake on your return

You can make corrections to your tax return within 12 months of the original deadline.

How you correct your tax return depends on how you filed it.

If you did your tax return online

  1. Log in to your HM Revenue and Customs (HMRC) online account.

  2. Click ‘At a glance’.

  3. Choose ‘Tax return options’.

  4. Select the tax year for the return you want to amend.

  5. Go into the tax return, make the corrections and file it again.

If you did a paper tax return

Get new forms, and send HMRC the corrected pages. Write ‘amendment’ on each page, and include your name and Unique Taxpayer Reference (UTR).

Check your Self Assessment paperwork for the address or send your corrections to the address for general Self Assessment enquiries.

If you used commercial software

Check with the software provider if you can correct your tax return. Contact HMRC if the software doesn’t let you make corrections.

Changes to your bill after you’ve made your corrections

HMRC will update your bill and let you know if you’re due a refund or owe more tax.

If you’re owed a refund

HMRC will let you know how much your refund is (including interest). Refunds can be:

  • paid electronically into your bank account
  • paid by cheque
  • deducted from your next Self Assessment tax bill - if it’s less than £10 or a tax bill is due shortly

Refunds usually take 4 weeks, or 6 weeks if you made paper corrections.

If you owe more tax

HMRC will let you know:

  • how much tax you owe (including interest) and the deadline for paying
  • if your advance payments towards next year’s bill, known as ‘payments on account’, will be more (if you’re paying them)

If you missed the deadline for sending corrections

If you didn’t send your corrections within 12 months of the original deadline, write to HMRC within 4 years of the end of the tax year you’re correcting.

Include in your letter:

  • why you think you’ve overpaid
  • the tax year you’re correcting
  • proof you paid the tax in that year
  • how you want the refund