This paper examines the relationship between calving date and production costs on Irish dairy farms from 2000-2007. Using data from the National Farm Survey, the median calving dates of 400 dairy farms are studied each year using econometric analysis to determine the relationship between calving date and production costs. Farms are divided into five categories according to their median calving date. These categories are imputed into a panel dataset as dummy variables. Unobservable individual effects are controlled for using a fixed effect model; examples of such effects are land quality and managerial ability, Results suggest that when scale and those unobserved effects are controlled for, there was no significant difference in total cost of production per litre according to median calving date