A baby’s normal temperature is similar to the average temperature of 98.6 degrees for adults, but it varies per child. A reading above 98.6 degrees doesn’t necessarily mean the baby has a fever, says Dr. Amin, as it’s normal for their temperature to fluctuate throughout the day. All our experts agree that a temperature above 100.4 degrees Fahrenheit taken rectally (99.5 degrees orally) is considered a fever, especially in babies under 3 months old. According to Dr. Stovall, a baby under 3 months with a 100.4 temperature must see a doctor immediately. Since newborns don’t always show us other signs of illness similar to older babies or children, doctors want to examine the “why” behind a fever, she says.  Remember: A fever doesn’t necessarily mean something serious is happening. Children who are still interested in playing, drink well, are alert and smiling with normal skin color, and look well with a lower temperature likely do not have a serious fever, Dr. Pitone explains. Although it’s always best to reach out to your child’s pediatrician for any concerns.