On many/all trading platforms you can’t. Your share trading platform will get out of sync with your tax returns.
Easiest option is to maintain a spreadsheet and then edit your buy price for your remaining shares on the trading platform. It’s a pain in the arse but not much choice.
I learnt about this when I had a tax loss carried over one year and sold some (not all shares) in a stock that fully covered that loss. My accountant tried to tell me that I needed to consider that the first shares I had bought were the first sold but I’d held them for more than 12 months and would have lost the CGT discount covering the prior loss with the gain. I told him I wanted the shares I sold to be some that I had bought more recently. At first he said I couldn’t do it but after some nagging and research he checked and confirmed I could.
It makes sense really. As soon as the trade is complete you own the shares. If you bought 1,000 IVZ 5 years ago in Commsec then bought 1,000 IVZ shares last Friday at 10am on NAB Trade, if you decide on Monday to sell 1,000 shares on NAB Trade it’s your choice which shares you tell the ATO you’ve sold. You own them all. They are not individually numbered right! A share is a share is a share.
This of course is not tax advice. Check with your accountant. And if they don’t tell you what you want to hear get a better one.
