This article reviews the importance of feed efficiency in heifer rearing and discusses potential factors that can modulate feed efficiency and their possible implications in future performance and economics of heifer rearing. Herein, we have gathered historical data from the largest contract heifer operation in Europe (Rancho Las Nieves, Mallén, Spain) to describe feed efficiency and economic returns throughout the rearing process. We have also compiled results from peer-review literature. Heifers represent the sustainability and future of the herd and are responsible for important economic costs as well as a considerable environmental impact. Factors influencing feed efficiency include age, type of ration fed, and environmental conditions. Feed efficiency is ~50% during the first 2 mo and progressively declines to ~7% before calving. Also, feed efficiency is affected by stocking density, physiological status of the animals, and diet nutrient composition, including the ratio between CP and ME. Regularly measuring feed intake and BW in dairy replacements is pivotal to improve heifer effectiveness and economics. Considering both, feed costs and feed efficiency, the most economically advantageous stage to foster body accretion in heifers is right after weaning until about 200 d of life. In addition, growth after weaning is positively correlated with future milking performance. Providing excessive amounts of forage after weaning should be avoided. Last, restricting the amount of diet fed to heifers, while maintaining an adequate supply of nutrients, may increase dietary unit costs and total daily feed costs.