Is a 98.6f temp underarm temperature considered a fever on a 9 months old baby?

Take rectal temp: For infants, a rectal temperature is the most accurate way to measure body temperature. A rectal temperature of 100.4F or greater is considered a fever in an infant. Make sure to treat the baby and not the number - if the baby is eating and drinking well, even with a fever, the baby can be managed at home. If the baby, however, is not drinking or urinating, go see your pediatrician!