I believe if you call / classify your self as a trader as of June 30 the stocks are valued at that date .
Sold or not .
Losses for the tax year are offset against the gains and any profit you pay tax on at your marginal rate .
The following year the cost base is at June 30 irrespective of what you originally paid .
No Capital Gains concessions apply to defined traders .
If you are not a trader then holding any asset eg shares for more than 12 months allows you a 50% discount on the gain
