Cow-calf producers face many annual decisions, as well as some less frequent but very fundamental decisions. A couple of those fundamental decisions include determining the appropriate calving season (e.g., spring or fall) and calving season length (e.g., 45, 60, 90 days). Approximately 67 percent of the cow-calf operations in the United States do not have a defined calving season (United States Department of Agriculture [USDA], 2009). This is despite research showing that a controlled calving season is more profitable than year-round calving (Doye et al., 2008). However, this decision can be difficult because nutritional demands, reproduction, calf performance and market prices have to be considered and evaluated. A Tennessee study by Henry et al. (2016) found that fall-calving herds had higher net returns and less variability in net returns than spring calving when marketing calves at weaning. However, less is known about the implication calving season length has on profitability for spring- and fall-calving cattle herds. Calving season length is defined here as the number of days from the start of calving to the end of calving. Given that many cow-calf producers in the United States sell calves at weaning (USDA, 2009) and that weaning is often based on producer convenience, calves born late in the calving season are often marketed at a lighter weight than early-born calves. Another drawback of a longer calving season is that late-calving cows have less time for uterine repair prior to the start of the next breeding season, which could negatively influence reproductive performance (Johnson, 2005; Mousel et al., 2012). A positive aspect of a longer breeding and calving season is that it provides more opportunities for cows to breed and wean a calf. Thus, there could be a trade-off between increasing weaning weight and calf uniformity and a lower percentage of cows bred in a shorter breeding season. Despite the aforementioned trade-off, there are reproductive management practices that can be utilized to address some of these challenges. One method is to cull openand late-calving cows and replace them with early-maturing heifers while also utilizing estrus synchronization (ES) and timed artificial insemination (TAI). These practices can narrow the calving window and produce a heavier and more uniform group of calves while maintaining a pregnancy rate that would be associated with a longer breeding season (Johnson, 2005; Johnson and Jones, 2008; Lamb and Mercadante, 2016). The objective of this research was to determine how calving season length influences net returns for spring- and fall-calving beef cattle herds in Tennessee. Data originated from a 19-year study in Tennessee of spring- and fall-calving herds. Production risk was evaluated for 45-, 60- and 90- day calving season lengths. Scenarios for 45- and 60-day calving season lengths that assume the producer used an improved reproductive management (IRM) practice to increase calving rates were also evaluated. Producers will benefit by better understanding the importance reproductive efficiency has on the profitability of the herd.