Key takeaways Australia's top marginal tax rate of 47% is one of the highest in the developed world, yet it was designed in 1915 as a temporary wartime measure targeting only the ultra-wealthy. When income tax was first introduced, the top rate only applied to those earning the equivalent of $960,000 in today's dollars, roughly 48 times the average wage. Today that same top rate kicks in at just 2.3 times the average wage, catching teachers, nurses, tradies, and property investors.