In general, PRSI contribution classes are decided by the nature of a person’s employment and the amount you earn in a week. Most workers pay PRSI contributions at Class A.
Class A covers employees under the age of 66 in industrial, commercial and service-type employment who have reckonable pay of €38 or more per week from all employments as well as Public Servants recruited from 6 April 1995.
If you log onto http://www.welfare.ie/publications/sw14.html you will see more information on each of the classes.
As you will see – Class A is further sub-divided into AO, AX, A1 A2 etc. The sub – category you are assigned is decided by the amount you earn e.g. if you earn more than €500 per week your sub-class is A1, if you earn between €356.01 - €500 per week your subclass is AL etc.
With regard to BIK – you can claim a tax credit for BIK paid on your health insurance if your employer pays this for you – you will need to contact Revenue to apply for this