Agree with Dave. A capital gain - or capital loss - is the...

Agree with Dave.

A capital gain - or capital loss - is the difference between what it cost you to get an asset and what you received when you disposed of it.

In this case $100 was invested, $100 was made from the transaction (for this financial year). When the second parcel of shares are sold (in another financial year) the Capital gain will then be incurred.

You don't pay tax on unrealised capital gains.