The national Lifetime Wool project has quantified the production benefits that accrue to a breeding flock of Merino ewes from actively managing their fat score at critical stages of the reproductive cycle. The GrassGro™ model was used to simulate the profitability of achieving three fat score targets (i.e. FS2.5, FS3-4% lambing and FS3-10% lambing) for a predominately grazing region (Yass) of NSW and a sheep/cereal region (Parkes). In both regions the FS3-10% flock had the highest gross margin but was also the riskiest option in terms of the variation in gross margin during the simulation period. In all cases the key driver of gross margin was the amount (and therefore cost) of supplement required to meet the fat score targets which highlights the importance of meeting the fat score targets using pasture and matching the breeding cycle to pasture availability. Merino producers can use this information to make informed decisions regarding whether or not to feed in dry years.