Sprat is a pelagic species of increasing commercial interest in European waters, yet little is known about its biology or the drivers of its population fluctuations. As a result, the species is currently without an analytical assessment or forecast across much of the North East Atlantic. The objectives of this study were to: verify otolithbased age estimation of sprat; assess the precision, bias and reproducibility of these age estimates; and, determine the age structure of sprat within one North East Atlantic management unit (Celtic Seas ecoregion). Samples were collected over three years (2011, 2013 & 2014) from both commercial catches and scientific surveys. Counts of daily increments in otoliths were used to establish when the first annulus was formed. The seasonal development of annuli was validated using marginal increment analysis. Age estimates were found to be both accurate and reproducible with no intra-reader bias and limited inter-reader bias (average coefficient of variation 2.7%). The age estimates indicate that the stock is comprised primarily of age 0, 1 and 2 year olds. This study has provided previously unavailable information on the biology and age structure of this species which is required to improve assessment and sustainable management of the species.