"The 2015 IGR projected that Australia's population would reach almost 40 million people by 2054-55. This IGR projects the population will reach 38.8 million in 2060-61. This is the first time there has been a downward revision of the population forecast in an IGR.", Federal Treasurer Josh Frydenberg said.
With fertility rates falling, the Treasurer says migrants will continue to be Australia's largest source of population growth.
The report highlights that with this ageing population, spending on health, aged care and the NDIS will also grow significantly.
Another factor affecting not just Australia but the whole world is climate change.