Self Assessment introduction
Self Assessment is not a tax. Self Assessment is the way HM Revenue & Customs (HMRC) collect income tax from those people who do not have approximately the correct amount of tax deducted from their income at source.
Most employees pay the correct amount of tax under the Pay As You Earn (PAYE) system and so do not need to complete a Self Assessment tax return. However, if you are self-employed or have significant amounts of untaxed income, for example rental income, then you will need to complete a tax return.
As an employee of the armed forces, you can find out more about why you might need to register for Self Assessment and complete a tax return in the tax basics section. If you do need to complete a tax return, it is important that you comply with all of the deadlines as HMRC will charge penalties if these are missed.
You can find out more about Self Assessment for people who are self-employed in the self-employment section.