This research investigates net present value–maximizing beef cow weights for U.S. Southern Plains cow–calf operations. The relationship between cow weight and calf weaning weight was estimated and weaning weights were simulated for a 15-year time period. Annual returns were computed using cow–calf revenues and production costs for cows with mature weight between 950 and 1,800 pounds. A grid search showed that optimal cow size was 950 pounds across scenarios. Selection for growth may improve feedlot profitability but has deleterious effects on cow–calf producers. Development of smaller-framed maternal lines may improve sector profits.