AA defines sober/sobriety as 'freedom from alcohol.' If the OP has not had any alcohol since his/her original sobriety date (4/9/11), as of today that person has 4 1/2 years of sobriety; at least according to AA (the organization not its individual members).
(o:
NoelleR
P.S. For specifics regarding this, see my previous post (#33).