Background: Language is a critical development accomplishment of early childhood, enabling later literacy, education and employment. Previous studies have highlighted socioeconomic inequalities in the amount parents speak to their child, with researchers estimating by age four parents from professional backgrounds spoke 30 million more words to their children, than parents who were on welfare. Methods: This study utilises innovative speech recognition technology called Language Environment Analysis (LENA), which counts the number of words children hear and speak over a day. LENA data is collected once every six months from 6 – 48 months of age, across two cohorts of children who are stratified by two levels of maternal education to examine the effects across socioeconomic groups. Results: Results from the first three waves of data collection demonstrate that differences between education groups in the number of adult words spoken to the child are not evident until the children are 18 months old. Average change in adult word counts per day by maternal education show there is a difference of 17 words at 6 months, 568 words at 12 months and 3,851 words at 18 months. Conclusions: This is the first study to be able to identify the age when socioeconomic differences in the amount of talk emerge. This has significant implications for the timing of interventions aiming to reduce the word gap, suggesting targeting the implementation of programs prior to 18 months. Key messages: Socioeconomic differences in the amount parents talk to their children do not emerge until children are 18 months old.