This study investigated whether reported amounts of money spent on gambling — when calculated retrospectively on a monthly basis — differ from the amounts recorded on a daily basis. Participants were required to retrospectively report monthly gambling expenditure and also complete a "daily gambling expenditure chart" for 4 weeks. Fifty participants responded to a media call for volunteers and completed the data collection. Results indicate that retrospective estimates of a previous month's expenditures tend to be lower than daily self-reported expenditures. Further, results show that an often-used, conventional self-report gambling question tends to over-estimate expenditures in comparison with calculations using a net expenditure strategy. The findings indicate important biases when reporting gambling losses, thus casting doubt on the validity of estimated gambling expenditures. The implications of these results suggest possible inconsistencies in gambling literature based on players' estimates of previous gambling expenditures.