It depends on whether you are talking about assessable income or...

It depends on whether you are talking about assessable income or tax payable. My understanding (which is not tax advice) is that if you trade out in less than 12 months any capital gain you make is assessable income which you then have to pay tax on. If you are in the top marginal tax bracket you will therefore end up paying approximately 50% tax on any gains you make. If you are in a lower tax bracket, the tax you pay will of course be lower.

If however you hold the shares for more than 12 months, any capital gains you make when you sell then are reduced by 50% when you report them as assessable income. Therefore if you were in the highest tax bracket the effective tax rate reduces to 25% (i.e. 50% of 50%).