There has been limited attention to estimating maternity rate because it appears to be relatively simple. However, when used for multi-annual breeder species, such as the largest carnivores, the most common estimators intro-duce an upward bias by excluding unproductive females. Using a simulated dataset based on published data, we com-pare the accuracy of maternity estimates derived from stan-dard methods against estimates derived from an alternative method. We show that standard methods overestimate mater-nity rates in the presence of unsuccessful pregnancies. Importantly, population growth rates derived from a matrix model parameterized with the biased estimates may indicate increasing populations although the populations are stable or even declining. We recommend the abandonment of the bi-ased standard methods and to instead use the unbiased alter-native method for population projections and assessments of population viability.