Infant mortality rate is the number of deaths of children under one year of age.

Some of the international variation in infant and neonatal mortality rates is due to variations among countries in registering practices of premature infants. Most countries have no gestational age or weight limits for mortality registration. However, some countries specify limits based on some combination of gestational age, birth weight or survival.

This indicator is measured as number of deaths per 1 000 live births.