In temperate rangelands, the timing of livestock breeding is managed so that most births occur late winter to midspring. Nutrient demands of young livestock increase steadily as they grow, while nutrients supplied by rangelands typically increase in spring and then decline through summer as plant tissues mature and senesce. Timing births in late winter rather than spring can increase weight gain of young livestock by ensuring young are larger and in need of more nutrition when forage quality is greatest, but this risks exposing newborns to lethal cold. We studied effects of calving date on weight gain and exposure risk of beef calves using 82 yr of data from the western United States. Our analysis indicated that, averaged over study years, 180-d-old calves weighed 13% ± 5.0% more (mean, 95% confidence interval) when born at the beginning (early March) compared with the end (early May) of our studied calving interval. Early calving likewise appeared to benefit calf production (weight of 180-d-old surviving calves per calf born), with benefits increasing as climate warming reduced neonatal mortality from cold exposure. Compared with calf production from early May calving, estimated calf production from early March calving was 8% ± 4% greater in the 1940s and 10% ± 4% greater in the 2010s (P < 0.001). Continued late winter and early spring warming would further increase benefits of early calving.