A babys normal temperature can range from about 97 to 100.3 degrees Fahrenheit (36.4 to 37.9 degrees Celsius) . A fever is an elevated body temperature, and it is usually considered to be a temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher. Different ways of measuring a temperature include rectal, armpit, ear, forehead, and mouth. The most accurate way to take a temperature for infants younger than 3 months is rectally. For infants between 3 months and 4 years old, rectal or forehead temperatures are accurate, and an ear thermometer can be used after 6 months old. Armpit temperatures are the least accurate but can be used for screening at any age. If a baby is younger than 3 months and has a fever, it is considered an emergency, and medical attention should be sought immediately. If a baby is between 3 and 6 months old and has a temperature up to 102 degrees Fahrenheit (38.9 degrees Celsius) and seems unusually irritable, lethargic, or uncomfortable, or has a temperature higher than 102 degrees Fahrenheit (38.9 degrees Celsius), medical attention should be sought. If a baby is older than 6 months and has a temperature higher than 102 degrees Fahrenheit (38.9 degrees Celsius) that lasts longer than one day but shows no other signs of illness, medical attention should be sought.