There are three types of Scheme Membership – Active, Deferred and Pensioner.
The length of your Scheme Membership for Active or Deferred members (those who haven’t yet claimed their pension) is the length of time you have contributed to the Pension Scheme – calendar length for the 2015 Scheme but more complicated for the 1995 Scheme and 2008 Scheme when part-time working counted as part-years’ membership
Lots more information on our 1995 Scheme and 2008 Scheme pages