A normal temperature for a baby ranges from 97°F to 100.4°F (36.1°C to 38°C). Anything at or above 100.4°F is considered a fever. That range is wider than most parents expect, and where your baby’s temperature falls within it depends on the time of day, how active they’ve been, and how you took the reading.
The Normal Range and What Counts as a Fever
The American Academy of Pediatrics defines 100.4°F (38°C) as the cutoff for fever in infants. Below that, your baby’s temperature is considered normal, even if it seems high to you. A reading of 99.5°F after a nap or a crying spell is perfectly typical.
Babies don’t hold a steady 98.6°F the way many parents assume. That number is just an average. Body temperature naturally dips in the early morning and peaks in the late afternoon and evening. Newborns already show this pattern within days of birth, and the daily swings become more pronounced by around four weeks of age. So a reading of 97.3°F first thing in the morning and 99.8°F before bedtime can both be completely normal for the same baby on the same day.
Other everyday factors push the number around too. A warm room, a thick swaddle, recent feeding, or a bout of crying can all nudge a baby’s temperature up temporarily without meaning anything is wrong. If you get a borderline reading, wait 15 to 20 minutes, remove a layer of clothing, and check again.
How to Take Your Baby’s Temperature Accurately
The method you use matters more than most parents realize. Each type of thermometer reads slightly differently, and some are far more reliable than others for babies.
Rectal (bottom): This is the gold standard for babies under 3 months. It gives the most accurate core body temperature. If you use any other method and get a concerning result, a rectal reading is the way to confirm it.
Temporal artery (forehead): Forehead thermometers are nearly as accurate as rectal ones and much easier to use. They’re a good option for babies 3 months and older, and recent research suggests they can also provide reliable readings in newborns.
Tympanic (ear): Ear thermometers are not recommended for babies younger than 6 months. A small, curved ear canal or a bit of earwax can throw off the reading. After 6 months, they become a reasonable choice.
Axillary (armpit): Armpit readings are the least accurate of all methods. They can be used as a quick first check for a baby of any age, but if the number looks worrisome, follow up with a rectal thermometer. Armpit temperatures tend to read lower than the true core temperature, so a “normal” armpit reading doesn’t always rule out a fever.
Why Age Matters With Fever
A fever of 100.4°F means very different things depending on how old your baby is. In the first two months of life, a baby’s immune system is still immature, and a fever can be the only visible sign of a serious infection. The AAP’s clinical guidelines break this vulnerable window into specific age groups: 8 to 21 days, 22 to 28 days, and 29 to 60 days, each with its own evaluation steps.
For babies under 2 months, any rectal temperature of 100.4°F or higher needs prompt medical attention, even if the baby looks fine otherwise. More than 10% of febrile infants in this age group turn out to have a urinary tract infection. More serious infections like meningitis are rare (fewer than 0.05% of cases), but the stakes are high enough that doctors take every fever in a young infant seriously.
For older babies, between 3 and 12 months, a fever on its own is less alarming. At that age, how your baby is acting tells you more than the number on the thermometer. A baby with a 101°F temperature who is feeding well, making eye contact, and wetting diapers normally is in a very different situation than one who is limp, refusing to eat, or hard to wake.
Febrile Seizures
Some children experience seizures triggered by fever, called febrile seizures. These can happen at any fever level, even a low-grade one just above 100.4°F. They’re most common between 6 months and 5 years of age. A febrile seizure typically involves stiffening, shaking, or eye rolling that lasts less than a few minutes. While terrifying to watch, febrile seizures are generally not harmful and don’t cause lasting neurological damage. They tend to run in families.
Keeping Your Baby’s Temperature Stable
Babies lose and gain heat faster than adults because of their higher skin-surface-to-body-weight ratio. That makes room temperature and clothing choices genuinely important. A room temperature below about 79°F (26°C) is considered safe for most infants. Above that, especially for prolonged periods, overheating becomes a concern.
A good rule of thumb is to dress your baby in one layer more than what you’re comfortable wearing. If you’re fine in a t-shirt, your baby probably needs a onesie plus a light swaddle or sleep sack. Feel the back of your baby’s neck or chest to gauge warmth. Hands and feet are naturally cooler in babies and aren’t a reliable indicator. If the skin on their chest or neck feels hot, sweaty, or flushed, they’re likely overdressed or the room is too warm. Overheating can mimic a low-grade fever on a thermometer, so it’s worth adjusting the environment before assuming your baby is sick.