The "Deadline for filing Self Assessment and Capital Gains Tax" is the final date by which individuals in the United Kingdom must submit their Self Assessment tax returns and Capital Gains Tax information to HM Revenue and Customs (HMRC). Self Assessment is a system used to report income, expenses, and other relevant financial details to determine the amount of tax owed. Capital Gains Tax, on the other hand, is applicable when individuals sell or dispose of certain assets and make a profit. The deadline for filing Self Assessment and Capital Gains Tax returns typically falls on the same day, which is an important deadline to meet to avoid penalties or late filing fees. It's worth noting that the specific deadline may vary each year, so individuals should consult the latest HMRC guidelines or official resources to determine the exact date for a particular tax year.