Canberrans have fewer babies than other Australians but the city is growing faster than the rest of the country.
The latest population projections suggest the national capital will be home to half a million people 10 years from now – about a year earlier than was suggested in modelling five years ago.
The ACT presently has about 420,000 residents.
A relatively large number of interstate arrivals, rather than overseas migrants, are feeding Canberra's boom.
Chief Minister Andrew Barr said his government had been planning for the increase, so as to avoid the congestion and strain on infrastructure experienced by Sydneysiders and Melburnians.
"Canberra is the best city in Australia to live in and ranked No. 1 or 2 in the world," he said on Thursday.
"This anticipated population growth is why we have started building a city-wide light-rail network to provide an integrated public transport network for Canberra, and it's why we continue to make record investments in our public health and education systems."
The Australian Bureau of Statistics bases its 50-year projections on existing demographic trends. It also includes high and low-growth projections, to allow for changes in population health and migration policies.
Its furthest projection, looking ahead five decades, suggests Canberra will have between 612,000 and 939,000 residents in 2066.
By then, Australia will have two global megacities. Melbourne, Australia's largest, will house from 8.6 million to 12.2 million people; Sydney will have between 8.5 million and 11.2 million.
The ACT is gaining about 8700 residents a year. Its growth rate is about 25 per cent faster than Australia's.
Of that growth, about 3800 are from "natural increase" (the net gain from births and deaths), another 3900 are overseas migrants, and 1000 are people resettling from interstate.
The ACT's share of interstate migration is particularly high. By comparison, Sydney loses about 20,000 residents each year to other parts of the country.
The Morrison government recently announced a "population plan", which involves cutting the overseas intake and forcing new migrants to live in areas other than Sydney and Melbourne.
Population Minister Alan Tudge said on Thursday the Prime Minister would soon ask premiers and chief ministers to "inform him of what their population-carrying capacity is for their existing and planned infrastructure and services".
However, Mr Barr criticised the Coalition's announcement, saying the ACT government was "not in the business of dog-whistling on population".
"Instead, we are making the right decisions now to avoid the congestion and housing issues we see in Sydney and Melbourne."