NIM39110 - National Insurance Numbers (NINOs): Format and Security: What a NINO looks like You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals. A NINO is made up of 2 letters, 6 numbers and a final letter, which is always A, B, C, or D. It looks something like this: QQ 12 34 56 A This is an example only and should not be used as an actual number. The Prefix Currently a prefix is chosen and then used until all the possible numbers have been allocated. Then another prefix is used, but not necessarily the next one alphabetically.