What is a normal temperature for a baby?

A normal body temperature for a baby is roughly 97.5F to 100.3F (36.4C to 37.8C), with an average close to 98.6F (37C). Temperature can shift by up to about 1 degree Fahrenheit across the day, running lowest in the early morning and highest in the late afternoon and evening. Because of this natural variation, a single reading close to the top of the range is not cause for alarm on its own.

What temperature is a fever in a baby?

The American Academy of Pediatrics defines a fever in a baby as a rectal temperature of 100.4F (38C) or higher. An armpit (axillary) reading of 99F (37.2C) or higher can also indicate a fever, though armpit readings are less reliable. Always confirm a suspected fever with a rectal reading, especially in babies under 3 months old, because the rectal method is the most accurate.

How do I take a baby's temperature?

For babies under 3 months, the American Academy of Pediatrics recommends a rectal thermometer as the only reliable method. Apply a small amount of petroleum jelly to the tip, gently insert it about half an inch to one inch into the rectum, and hold it in place until it beeps. For older infants, an armpit reading gives a useful first screen. Ear and forehead thermometers are convenient but less reliable in very young babies, and ear thermometers should not be used before 6 months.

When should I call the doctor about a baby's fever?

Any baby under 3 months old with a rectal temperature of 100.4F (38C) or higher needs to be seen or assessed by a doctor the same day, and a baby under 2 months with any fever is a medical emergency. For babies 3 to 6 months, call your pediatrician for a rectal reading of 101F (38.3C) or higher, or for any fever that worries you. For babies 6 months and older, call if the fever reaches 103F (39.4C) or is accompanied by other concerning symptoms such as difficulty breathing, a rash, or unusual drowsiness.

Is a low body temperature in a baby dangerous?

A temperature below 97.5F (36.4C) in a baby, called hypothermia, is worth taking seriously. It can signal that a baby is unwell, particularly in newborns and premature infants who have difficulty regulating their own body heat. If a young infant reads below 97F (36.1C), contact your pediatrician or seek medical advice promptly. Keeping babies warm and avoiding overdressing (which can mask early signs) are both important.

Should I worry if my baby feels warm?

Feeling warm to the touch is a reason to take a temperature with a thermometer rather than a reason to panic. Babies can feel flushed after feeding, being bundled up, or being held, and these are not signs of illness. A thermometer gives the only reliable reading. If the rectal temperature is 100.4F (38C) or higher, follow the age-based guidance above and contact your doctor if needed.

Normal Temperature for Babies and Newborns

A normal body temperature for a baby is roughly 97.5F to 100.3F (36.4C to 37.8C), and a fever is a rectal reading of 100.4F (38C) or higher. That single threshold is the most important number on this page. It is the standard used by the American Academy of Pediatrics (AAP), the Mayo Clinic, and major children's hospitals including Boston Children's and Children's Hospital of Philadelphia. If your baby's rectal temperature reaches or exceeds 100.4F (38C), the age of your baby determines how urgently you need to act.

This article is general health information and is not a substitute for professional medical advice. If you are concerned about your baby's temperature or health, contact your pediatrician or a healthcare provider right away. In an emergency, call 911 or go to the nearest emergency room.

Temperature in babies is a topic that causes real anxiety for new parents, partly because the numbers in Fahrenheit and Celsius appear on different thermometers and in different guidelines, making a simple reading feel confusing. This guide puts both scales in the same tables, explains which measurement method is most reliable, and tells you clearly when to call the doctor and when to treat a fever as an emergency. For broader context on fever thresholds, see our articles on what temperature is a fever and normal body temperature.

Normal versus fever: the key temperature ranges

Body temperature in babies is not a fixed number. It drifts by up to about 1 degree Fahrenheit across the day, lowest in the early morning and highest in the late afternoon and evening. The AAP and the Mayo Clinic describe the ranges in the table below using rectal (or equivalent core) readings, which are the gold standard for infants.

Category	Fahrenheit	Celsius
Normal range	97.5F to 100.3F	36.4C to 37.8C
Low-grade fever	100.4F to 101.9F	38.0C to 38.8C
Fever	102.0F and above	38.9C and above
Low temperature (hypothermia)	Below 97.5F	Below 36.4C (also warrants a call for a young infant)

The single most important figure to know is 100.4F (38C). At or above that rectal reading your baby has a fever, and the next step depends entirely on age. The low-grade category above is included for completeness, but clinically the 100.4F (38C) line is where guidelines begin, not 101F or 102F.

Measurement methods: which thermometer to use and when

Not all thermometers read the same site, and that matters. A rectal reading measures temperature closest to the body's core, which is why the AAP recommends it as the most accurate method for babies, particularly those under 3 months old. Other methods are useful as a screen or for older infants, but a rectal reading is what you need before calling a doctor about a possible fever in a young baby.

Method	Best for	Notes
Rectal	All babies, required for under 3 months	Most accurate method. Insert the lubricated tip about half an inch to one inch. A rectal fever threshold is 100.4F (38C) or higher.
Armpit (axillary)	Screening check for infants 3 months and older	Runs 0.5F to 1F lower than core temperature. An armpit reading of 99F (37.2C) or higher suggests fever, but confirm with a rectal reading in young babies.
Ear (tympanic)	Children 6 months and older only	Not reliable in babies under 6 months because the ear canal is too small and too curved for an accurate reading. Earwax can also affect results.
Forehead (temporal artery)	Convenient screen for all ages	Fast and non-invasive, but highly technique-sensitive. Sweat, hair, or an incorrect sweep angle can cause a falsely low reading. Always confirm concerns with a rectal thermometer in young babies.

When you call your pediatrician or describe a temperature to a nurse line, always say which method you used. A reading of 99.5F means something different depending on whether it was taken rectally, under the arm, or on the forehead.

When to call the doctor and when it is an emergency

Age is the single most important factor in deciding how urgently to act on a baby fever. Young infants have immature immune systems and can become seriously ill very quickly, often without showing obvious outward signs. The guidance below is drawn from the AAP, the Mayo Clinic, and Boston Children's Hospital.

Under 2 months: treat as an emergency. Any rectal temperature of 100.4F (38C) or higher in a baby under 2 months old is a medical emergency. Go to the emergency room or call 911. Do not wait to see if the fever comes down on its own.
2 to 3 months: call the doctor the same day. Any rectal temperature of 100.4F (38C) or higher needs to be assessed by your doctor within hours. Do not give fever-reducing medication before being seen, as this can mask important clinical signs.
3 to 6 months: call your pediatrician. A rectal temperature of 101F (38.3C) or higher, or any fever that worries you, warrants a call to your doctor. If your baby is unusually drowsy, has difficulty breathing, is not feeding, or has a rash, seek care promptly.
6 months and older: call for a high fever or concerning signs. A temperature of 103F (39.4C) or higher is a reason to call. Also call if a fever lasts more than two days, returns after going away, or is accompanied by symptoms such as ear pain, persistent crying, difficulty breathing, a rash, or poor fluid intake.
At any age: seek emergency care for these warning signs. A fever paired with a stiff neck, severe headache, a rash that does not fade when pressed, a seizure, unusual difficulty waking the baby, or any signs of breathing trouble is an emergency regardless of how high the temperature reads.

These guidelines are not exhaustive. Trust your instincts. If something about your baby feels wrong, seek medical advice without waiting, even if the temperature is within a number range that looks normal.

How to take a baby's temperature accurately

Getting a reliable reading starts with the right equipment and the right technique. Use a digital thermometer rather than an old mercury one. For babies under 3 months, the AAP recommends a rectal reading every time, even if it takes a moment longer. Here is how to do it safely.

Clean the thermometer with soap and warm water or rubbing alcohol, then rinse and let it dry.
Apply a small dab of petroleum jelly (such as Vaseline) to the tip of the thermometer.
Lay your baby on their back and gently hold both ankles, lifting the legs slightly as you would for a diaper change.
Gently insert the thermometer tip about half an inch to one inch into the rectum. Do not force it. Hold it loosely in place until the thermometer beeps.
Remove the thermometer and read the number. Write it down along with the time and the method used.
For armpit readings, place the tip in the center of the armpit, hold the arm snugly against the body, and wait for the beep. Add approximately 0.5F to 1F to estimate the core temperature if you are comparing to a fever threshold.

Avoid taking an oral temperature in children under 4 years old, as they cannot hold a thermometer safely under the tongue. Also avoid taking a temperature within 20 to 30 minutes of a bath or after the baby has been heavily bundled, as both can temporarily raise a surface reading.

What a low temperature in a baby can mean

Most fever articles focus on temperatures that are too high, but a low temperature in a baby is also a reason to pay attention. The medical term is hypothermia, and in a newborn or young infant it can indicate illness, infection, or the baby's inability to maintain their own body heat, which is common in premature infants and newborns in the first days of life.

A rectal temperature below 97.5F (36.4C) in a baby warrants a call to your pediatrician. A reading below 97F (36.1C) in a young infant is cause for more urgent concern. Warming the baby by skin-to-skin contact with a parent and making sure they are not in a cold environment is appropriate immediate care, but this does not replace a call to a doctor. Children's Hospital of Philadelphia and the Mayo Clinic both note that hypothermia in newborns can be a sign of serious infection (sepsis), and it should be taken as seriously as a high fever.

A low reading can also result from a measurement error, most often a poorly placed armpit thermometer. If you get an unexpectedly low result, take a rectal reading to confirm before calling.

Daily temperature variation and what affects a baby's reading

Even a healthy baby's temperature is not steady throughout the day. It follows a natural rhythm called the circadian temperature cycle, trending lower in the early morning and higher in the late afternoon and early evening. This variation can be as much as 1 degree Fahrenheit in either direction from the daily average. A reading near the top of the normal range (close to 100.3F / 37.8C) taken late in the afternoon is less alarming than the same number at 3 a.m.

Several other factors can temporarily influence a surface reading. Being heavily dressed or swaddled, recent physical activity such as crying, and a warm bath can all raise a skin or armpit temperature modestly. These factors have less effect on a rectal reading, which is another reason it is the preferred method for young babies. If you are unsure whether a high reading is real, undress your baby for ten minutes and retake the temperature rectally.