For a scenario of going over the 6 years this is the formula:
(Market value at the date first rented out) x (non main residence days ? ie over 6 years)/ (days in deemed ownership period).
For a scenario of going over the 6 years this is the formula:
(Market value at the date first rented out) x (non main residence days ? ie over 6 years)/ (days in deemed ownership period).
Have a look at the legislation, s118-145 ITAA97. It is very clear and even has an example which proves your accountant wrong:
see http://www.austlii.edu.au/au/legis/cth/consol_act/itaa1997240/s118.145.html