Brazilian beef cattle farming stands out for its large-scale production, playing a vital role in national and international trade. Despite this, there is a need for improvement in productivity and profitability. The extensive model, despite territorial demand, exhibits low use of technologies and problematic management. Intensive livestock farming minimizes these issues, offering greater production efficiency by reducing the age at which cattle are finished and optimizing the use of space on the property. The choice of diet in confinement systems aims to enhance the cost/benefit ratio. This research aims to compare the performance of Nelore cattle subjected to different diets during the finishing phase in confinement, considering intake, productivity, carcass characteristics, and economic viability. For the experiment, 20 Nellore cattle were used, divided into two groups of 10 animals, where one received the treatment of feed + forage, and the other a high-grain diet. For the variables of average daily gain (ADG), total weight gain (TWG), and feed-lot time, there was no effect (P < 0.05) from the treatments. However, an effect (P < 0.05) on carcass yield between diets was observed, directly impacting the economic viability of beef cattle production, as the abattoir pays per kilogram (cwt) of carcass.