A healthy baby’s temperature typically sits around 98.6°F (37.0°C), but anything from 97°F to 100.4°F (36.1°C to 38.0°C) is considered normal. That range surprises many parents, but babies’ temperatures shift throughout the day based on activity, clothing, feeding, and even the time of day.
The Normal Range
The American Academy of Pediatrics considers a normal temperature for a child to be anywhere from 97°F to 100.4°F. A reading at the higher end of that range doesn’t automatically mean something is wrong. Babies run warmer after a feeding, a crying spell, or time spent bundled up. Their temperature also tends to be slightly lower in the morning and slightly higher in the late afternoon and evening.
Once a rectal temperature hits 100.4°F (38.0°C) or above, it’s considered a possible fever. That single number is the threshold pediatricians use across the board, regardless of whether your baby is two weeks old or ten months old.
Why the Thermometer Type Matters
Not all thermometers give you the same number, and the method you use changes how accurate that reading is. Rectal and oral temperatures are the most reliable. Armpit (axillary) and ear (tympanic) readings are less precise and can run lower than the actual core temperature.
For babies under three months old, a rectal thermometer is the recommended method. It gives the closest reading to true body temperature. If you take an armpit reading and it seems elevated, follow up with a rectal reading to confirm. Ear thermometers aren’t reliable for very young infants because the ear canal is too small for an accurate measurement.
To take a rectal temperature, lubricate the tip of a digital thermometer, insert it about half an inch, and hold it in place until it beeps. The whole process takes under a minute.
When a Fever Becomes Urgent
A fever of 100.4°F or higher means different things at different ages. Age is the single most important factor in deciding how serious a baby’s fever is.
- Birth to 8 weeks: Any rectal temperature of 100.4°F or above needs immediate medical evaluation. At this age, babies have immature immune systems, and a fever can signal a serious infection that isn’t obvious from the outside. Hospitals follow specific protocols for febrile infants under 56 days old that include blood work, urine tests, and sometimes a spinal fluid check to rule out bacterial infections.
- 2 to 3 months: A fever still warrants a call to your pediatrician the same day. Your baby may need to be seen in person, depending on how they’re acting and whether other symptoms are present.
- 3 to 12 months: A fever alone is less alarming at this age if your baby is feeding well, making wet diapers, and acting relatively normal. How your baby looks and behaves matters more than the number on the thermometer. A baby with 101°F who is playful and drinking well is in a very different situation than a baby with 100.5°F who is limp and unresponsive.
Warning Signs Beyond the Number
Temperature is only one piece of the picture. Certain symptoms alongside a fever signal that something more serious may be happening.
Watch for unusual sleepiness or difficulty waking your baby. A baby who feels floppy when you pick them up, or who is crying inconsolably and can’t be soothed, needs prompt attention. Skin or lips that look blue, purple, or gray point to a breathing or circulation problem.
Dehydration is another concern during any illness with fever. Signs include fewer wet diapers than usual, crying with few or no tears, a dry mouth, and a sunken soft spot on top of the head. Sunken eyes and unusual drowsiness or irritability can also indicate your baby isn’t getting enough fluid. If you’re breastfeeding or bottle-feeding, offer smaller, more frequent feeds to keep fluids up.
A rash that appears suddenly alongside a fever, especially one that blisters or looks infected, is another reason to call right away. Trouble breathing, including flaring nostrils, grunting, or visible rib pulling with each breath, needs immediate care regardless of what the thermometer says.
Keeping Your Baby at a Comfortable Temperature
The room where your baby sleeps plays a bigger role in body temperature than many parents realize. The recommended nursery temperature is 68 to 72°F (20 to 22°C) year-round. A room that’s too warm increases the risk of overheating during sleep, which is a known risk factor for SIDS.
A good rule of thumb: dress your baby in one layer more than what you’d wear comfortably in the same room. If you’re fine in a T-shirt, your baby likely needs a onesie plus a light sleep sack. Hats, heavy blankets, and extra layers in a warm room can push body temperature higher than it needs to be. If your baby’s chest or back of the neck feels hot and sweaty to the touch, they’re overdressed.
When checking whether your baby feels warm due to the environment versus illness, remove a layer, wait 15 to 20 minutes, and retake the temperature. If it drops back into the normal range, overheating was the likely cause rather than a fever.
How to Get an Accurate Reading
Timing and technique both affect accuracy. Avoid taking a temperature right after a bath, a feeding, or heavy swaddling, since all of these can temporarily raise the reading. Wait at least 15 minutes after any of these activities.
If your baby’s first reading is borderline, around 99.5°F to 100.3°F, recheck in 15 to 30 minutes. A single slightly elevated reading doesn’t confirm a fever. Two consistent readings give you a clearer picture. Write down the time, the reading, and the method you used so you can share accurate information if you need to call your pediatrician.