Page "National Insurance number" Paragraph 8

Until 1975, the suffixes A, B, C and D at the end of the NI number signified the period of validity of the National Insurance cards originally used to collect National Insurance contributions ( NICs ).

Cards were exchanged every twelve months and because of the very large numbers of cards issued the exchange was staggered.

Suffix A cards ran from March of one year until March of the next when they were exchanged for a new one.

Stagger B suffix cards ran from June until the following June, stagger C from September until the following September and stagger D from December until the following December.

For example a B stagger card issued in 1955 might have run from the first Monday in June that year until the first Sunday in June the following year.

This staggered system operated from 5 July 1948 until 1975, at which time the A stagger cards were extended to run an extra five weeks, until 5 April 1975, in line with the end of the tax year.

The B, C and D stagger NI Cards had a shorter period of validity in their final year, and ran from June, September and December respectively until 6 April 1975.

From 6 April 1975 onwards, a computerised National Insurance Recording System ( NIRS ) was used to allocate all NICs by tax years.