Business information analysts IBIS World predicted that Australia's population would reach 25.7 million by 2020 with women still outnumbering men.
Analysts said on Wednesday more boys were born each year than girls, but men's life expectancy was shorter than women resulting in 101 females for every 100 males in 2008.
A record 287,500 babies were born in Australia in the year ended June 2008.
IBIS World general manager for Australia Robert Bryant said the fertility rate also increased to 1.91 babies per woman - rising for the fifth consecutive year and the highest result since 1994.
However, he said migrants would eventually be the only form of population growth for the country.
"Looking ahead, net migration to Australia will total around 2.5 million between now and mid-2020, eventually becoming the only form of population growth in this country as our aging population and comparatively low fertility rate will cause the number of annual deaths to overtake the number of babies born, probably sometime in the 2030s," Bryant said.
He added four million (20 percent) of Australians were born overseas with the United Kingdom, Ireland, New Zealand and Italy being among the top birth places.