The timing and synchrony of mating activity in a population may vary both within and among years. With the exception of masting species, in which reproductive activity fluctuates dramatically among years, mating synchrony is typically studied within years. However, opportunities to mate also vary among years in non-masting iteroparous species. We demonstrate that studying only within-year flowering synchrony fails to accurately quantify mating opportunity in an experimental population (n = 286) of a non-masting species, Echinacea angustifolia. We quantified individuals' synchrony of flowering within and among years and partitioned the contribution of each measure to mean daily mating potential, the number of potential mates per individual per day averaged over every day it flowered during the 11-year study period. Individual within- and among-year synchrony displayed wide variation and were weakly correlated. Each contributed to mean daily mating potential to differing extents, indicating that consequences of flowering synchrony, such as mate availability, vary in magnitude between temporal scales. In particular, among-year synchrony explained 39% more variation in mean daily mating potential than did within-year synchrony. Thus, among-year synchrony likely has underappreciated significance for mating dynamics in non-masting species.