AUSTRALIA's population clock is expected to tick over to 24 million people just after midnight tonight - 17 years earlier than previously predicted. 
The population is predicted to hit the milestone at 12.51am tomorrow. Demographer Andrew Howe said the clock calculated the growth by adding one person every 91 seconds.
"It's our best estimate based on current trends in migration, birth rates and death rates," he said.
"We keep creeping up - currently we're increasing an extra one million people every three years." The population clock is based on one birth every one minute and 44 seconds, one death every three minutes and 24 seconds, and a net gain of one migrant every two minutes and 39 seconds.
The milestone follows record overseas migration, which made up more than half of the population increase in the 12 months to   July last year.There were nearly twice as many births (304,000) as deaths (155,000) last year.