The critical date is 1 July 2027. Under the transitional arrangements, taxpayers will generally need to either use a market value as at 1 July 2027 to calculate the pre- and post-transition portions of any eventual gain or apply an ATO-approved apportionment method, for example, a time-based formula. Which approach applies, and how it's calculated, will depend on ATO guidance that is still to come. Getting a well-supported market value at 1 July 2027 locked in now creates the clearest baseline.