<P> The National Insurance number is a number used in the United Kingdom in the administration of the National Insurance or social security system . It is also used for some purposes in the UK tax system . The number is described by the United Kingdom government as a "personal account number". </P> <P> The number is sometimes referred to as a NI No or NINO . </P> <P> People born and resident in the UK are assigned a Child Reference Number shortly after birth when a claim is made for Child Benefit . At age 15 years 9 months HM Revenue and Customs (HMRC) notifies each child of their NI number . </P> <P> In 1993, a one - off mass allocation of NI numbers was made to all children under the age of 16 whose parents were in receipt of Child Benefit . As a result of this, siblings who met the criteria above were allocated NI numbers sequentially . </P>

When does your national insurance number come through