File an amended tax return

The amendment window for a Tax Return year ends midnight GMT 12 months from the statutory filing date for the return. For online returns this would be 31 January. If you used the HM Revenue & Customs (HMRC) Self Assessment Service to file the original Tax Return for the year (or a previous amendment) you may file an amendment using the HMRC Self Assessment Service from the next day. Otherwise you may similarly file an amendment using commercial software.

Amendments can be filed online at daily intervals and it is possible, if necessary, to make a total of 9 online amendments within the amendment window. Where an attachment(s) formed part of an original Tax Return submission (or previous amendment) it is not necessary for them to be re-attached to a subsequent amendment. You can however choose to re-attach the same attachment(s), or a different one(s), with your amendment. The amendment facility can not be used simply to send in an attachment without an alteration in the content of the return itself.