It’s well established that unsustainable human activity is damaging the health of the planet. The way we use Earth threatens our future and that of many animals and plants. Species extinction is an inevitable end point. It’s important that the loss of Australian nature be quantified accurately. To date, putting an exact figure on the number of extinct species has been challenging. But in the most comprehensive assessment of its kind, our research has confirmed that 100 endemic Australian species living in 1788 are now validly listed as extinct. Alarmingly, this tally confirms that the number of extinct Australian species is much higher than previously thought.