Each time you buy shares (either via your commsec or in an SPP) you can think of it as a parcel. Each parcel has its own cost base which is treated differently when you dispose of them. So when you sell all your shares the cost base will be the sum of the cost of each parcel. Each parcel also has its own date of purchase so if applicable, apply a discount to the parcels which are eligible only. Can explain more if needed otherwise get the ATO CGT guide for personal investors for free off the ATO website it's brilliant.
