You have not provided enough detail in your Q to tell.
i.e. If this was your only home - then NO, in this scenario there is no CGT.
If this was your only home and you had done the same thing 6 times this year, then the ATO may see you as running a business and then either PAYG or CGT may apply.
If this was not your only home, then yes, CGT would apply but you'd get a 50% discount on that if you held for over 12 months.
So....it all depends.
thanks that helps, it is my sons he has been in his own first home for 6 mths, done upn now just buying another, so will sell first, then do up 2nd while living in it. so there may be some implications if he sells that to soon