A healthy newborn’s body temperature sits between 97.7°F and 100.3°F (36.5°C to 38°C). The exact reading depends on where you measure, but anything in that range is normal. A rectal temperature of 100.4°F (38°C) or higher counts as a fever, and in babies under three months old, that number always warrants a call to your pediatrician.
Normal Range and What Counts as a Fever
Newborns run slightly warmer than adults. Their normal core temperature hovers around 98.6°F (37°C) but can fluctuate a degree or so in either direction throughout the day. After a feeding, a crying spell, or time spent bundled up, a reading on the higher end of normal is expected.
The critical threshold is 100.4°F (38°C) taken rectally. The American Academy of Pediatrics uses this cutoff for infants 8 to 60 days old. Below that number, there’s generally no concern. At or above it, the fever itself may be mild, but in a newborn whose immune system is still immature, even a low-grade fever can signal a serious infection. The AAP breaks its evaluation guidelines into three age windows (8 to 21 days, 22 to 28 days, and 29 to 60 days) because the risk profile changes rapidly in those early weeks.
When a Temperature Is Too Low
Cold is just as dangerous as heat for a newborn. The World Health Organization defines neonatal hypothermia as a core temperature below 97.7°F (36.5°C). Even before a baby’s reading drops that low, cold stress can set in, forcing the body to burn extra calories just to stay warm. That metabolic response increases oxygen demand by two to three times the normal rate, which is particularly risky for premature infants or babies with breathing difficulties.
Prolonged cold stress that goes unnoticed can also divert energy away from growth. If your baby feels cool to the touch on the chest or belly (not just the hands and feet, which are normally cooler), add a layer and recheck in 15 to 20 minutes.
How to Take a Newborn’s Temperature
For babies under three months, a rectal thermometer gives the most accurate reading. It measures core body temperature directly, which is why pediatricians rely on it. If you’re not comfortable with the rectal method, a forehead (temporal artery) thermometer is a reasonable alternative for a first check, though your pediatrician may ask you to confirm with a rectal reading if the baby seems sick.
Armpit (axillary) readings are the least reliable. They tend to run about a degree lower than rectal readings, so they can miss a fever entirely. Ear thermometers aren’t accurate in babies until around six months of age because the ear canal is too small for a proper seal.
Whichever method you use, take the temperature when your baby is calm. A screaming, recently fed, or heavily swaddled baby will read higher than baseline. If a first reading seems off, wait a few minutes and try again.
Room Temperature and Sleep Safety
The room where your baby sleeps plays a direct role in body temperature. The recommended range is 61°F to 68°F (16°C to 20°C). Keeping the nursery within that window helps lower the risk of sudden infant death syndrome (SIDS), because overheating is a known risk factor. A simple room thermometer on a shelf or wall takes the guesswork out of it.
To check whether your baby is comfortable, feel the skin on their chest or the back of their neck. Hands and feet that feel cool are normal and not a sign your baby is cold. If the chest feels hot or sweaty, remove a layer of clothing or bedding. A good rule of thumb is to dress your baby in one more layer than you’d wear comfortably in the same room.
Signs of Overheating
Overheating doesn’t always show up as a high number on a thermometer. Physical signs to watch for include skin that feels very warm to the touch (especially on the chest and back), damp or sweaty hair, flushed skin, faster breathing, and a rapid heartbeat. If your baby is sweating heavily and then stops sweating while their skin stays hot and dry, that’s a more serious sign of heat-related illness and needs prompt attention.
Common culprits are too many blanket layers, a hat left on indoors, a car seat cover that traps heat, or a room that’s warmer than you realize. Babies can’t kick off covers or tell you they’re uncomfortable, so regular spot checks matter more than you might expect in the first few months.
Quick Reference
- Normal body temperature: 97.7°F to 100.3°F (36.5°C to 38°C) rectally
- Fever threshold: 100.4°F (38°C) or higher rectally
- Hypothermia threshold: below 97.7°F (36.5°C)
- Ideal room temperature for sleep: 61°F to 68°F (16°C to 20°C)
- Best thermometer for newborns: rectal, followed by forehead as a backup