Quite simple (1) The NZ flag does not have the Commonwealth Star which is an integral part of the Australian flag (this is the six pointed star to represent the six founding states plus Australias territories, located under the Union Jack) (2) The NZ flag has the Southern Cross coloured red with white borders(rather than white on the Aussie flag) (3) The Southern Cross on the NZ flag only has four five-pointed stars (rather than five on the Aussie - four with seven points and one with five) (Typo on original answer incorrectly said the stars on the Aussie flag were blue - they are of course white
