The city is predicted to swell with an extra 25,000 people over the next four years, the ACT government's latest modelling predicts.

But while migration from overseas and interstate will play a role in the boom, a natural increase (births minus deaths) will account for 62 per cent of the growth.

In the year to June 2016, there was a natural increase of 3589 people in the ACT.

University of Melbourne demographer Professor Peter McDonald said the ACT's relatively high birth rate of 1.79 births per woman aged 15-49 was unusual, given our high education levels.

However, the birth rate was just shy of the national birth rate and behind other states and territories.

"It is interesting, though, because usually an area with a higher birth rate has lower education levels," he said.

Migration is set to drive 38 per cent of the growth; net overseas migration is expected to climb 65 per cent to 2650 people in 2019-20.

Interstate migration is predicted to turn around from a net loss of 176 people in 2015-16 to a gain of 130 people in 2019-20.

The report notes that, historically, overseas and interstate migration have proved to be "extremely volatile".

Professor McDonald said that while there was still a high number of people migrating from NSW to the ACT, Canberra was losing about 1000 people a year to Victoria and about 500 to Queensland.

"Most of these, it would be fair to say, are people who have retired and are looking to move back to where their kids are, like I myself just did, or move away from the cold," he said.

The number of people living in the ACT on June 30 last year was estimated to be 396,551. But by June 2020, the population is predicted to increase by 6 per cent to 421,839.

New residents are projected to flock to Canberra's burgeoning suburbs in the north and west. The population of the Cotter-Namadgi region is expected to explode by 139 per cent by 2020, thanks to new suburbs including Coombs, Denman Prospect and Riverview.

Gungahlin will be another hot spot for growth, with new suburbs like Crace helping to grow the population by 19 per cent by 2020.

The population of North Canberra is projected to grow by 8 per cent; South Canberra by 5 per cent; and Belconnen by 3 per cent.

Meanwhile, no population growth is predicted for the Woden Valley, Tuggeranong's population will decline by 3 per cent and Weston Creek's will fall by 7 per cent under the modelling.

But despite new suburbs drawing Canberra's population centre further north, Banks mother Nicole Tarling, 24, says her neighbourhood is full of young families.

Her decision to raise her two children in the Tuggeranong suburb was made with nearby family and a budget in mind, but she acknowledged the declining amenity could encourage more southside families to move northside.

"Tuggeranong is slowly developing, we're slowly getting more restaurants, more play centres but it definitely is frustrating," she said.

Similarly, Marnie Murrell, 30, is raising a 10-year-old stepdaughter, a 23-month-old daughter and a newborn in Calwell.

"I don't think Canberra brings families here but it's great for families," she said.