The survey, released to coincide with the launch of a national fertility awareness campaign today, showed that only 20 per cent of Australians knew that female fertility started declining in the early 30s.
The survey found that 30 per cent of men and 36 per cent of women wrongly thought women's fertility declined from 35 to 39.
Almost 20 per cent of men and women thought female fertility dropped off from the ages of 40 to 44.
Only nine per cent could identify that men's fertility starts sliding after age 45.
The new campaign, Your Fertility, aims to inform people who want children to make lifestyle choices to help them conceive healthy babies.
The Victorian Assisted Reproductive Treatment Authority (VARTA), Andrology Australia, Jean Hailes for Women's Health and the University of Adelaide's Robinson Institute are behind the campaign..
The study, commissioned by VARTA, surveyed 462 people aged 18 to 45 nationally who intended to have children.
In 2009, 14 per cent of Australian mothers who gave birth were 35 or older, compared with 10 per cent in 2000.