A fever in children is any body temperature at or above 100.4°F (38°C). That single number applies across all ages, from newborns to teenagers, and it’s the threshold used by the American Academy of Pediatrics. But what counts as concerning depends heavily on your child’s age, how you took the temperature, and what other symptoms are present.
The 100.4°F Threshold
Normal body temperature hovers around 98.6°F (37°C), though it naturally fluctuates throughout the day. It tends to be lowest in the morning and highest in the late afternoon. A reading of 100.4°F or above, taken accurately, is considered a fever regardless of the time of day.
That said, not all fevers carry the same urgency. A temperature of 101°F in a healthy three-year-old is usually manageable at home. The same reading in a baby under three months old is a different situation entirely, one that typically requires an immediate trip to the emergency department. Above 104°F (40°C) in any child warrants prompt medical attention.
Why the Thermometer Location Matters
Where you place the thermometer changes the reading you get. A rectal temperature is the most accurate for young children and the gold standard for babies. An armpit (axillary) reading typically runs about a degree lower than a rectal one, so a 99.4°F armpit reading could actually be a 100.4°F core temperature. Oral readings fall somewhere in between, and ear thermometers can vary depending on how well they’re positioned in the ear canal.
If you get a borderline number from an armpit or forehead reading and your child seems unwell, it’s worth rechecking with a more reliable method before deciding your next step.
Best Thermometer by Age
The right thermometer depends on how old your child is and what they’ll tolerate:
- Birth to 3 months: A standard digital thermometer used rectally gives the most reliable reading. Temporal artery (forehead) thermometers may also provide accurate results in newborns.
- 3 months to 4 years: Rectal remains the most accurate option, but armpit and forehead thermometers work as screening tools.
- 6 months and older: Digital ear thermometers become an option. Before six months, ear canals are too small for a reliable reading.
- 4 years and older: Most children can hold a digital thermometer under their tongue long enough for an oral reading. Ear, forehead, and armpit methods all work at this age too.
Fever in Babies Under 3 Months
A rectal temperature of 100.4°F or higher in an infant younger than three months is always treated seriously. Young babies have immature immune systems, so even a low-grade fever can signal a bacterial infection that needs rapid evaluation. Don’t wait to see if the fever resolves on its own, and don’t give fever-reducing medication first. Head to the emergency department.
For babies between 3 and 6 months, a fever above 102°F or one that persists beyond a day still warrants a call to your pediatrician, even if your baby seems comfortable.
Managing a Fever at Home
For older infants and children, a fever itself isn’t dangerous. It’s the body’s natural response to infection, and bringing the number down doesn’t cure the illness. The goal of treatment is comfort, not hitting a specific temperature on the thermometer.
Two over-the-counter medications help with fever and discomfort. Acetaminophen (Tylenol) can be given every 4 to 6 hours, up to five times in 24 hours. Ibuprofen (Motrin, Advil) can be given every 6 to 8 hours, up to four times in 24 hours. Both are dosed by your child’s weight, not age. Check the packaging or ask your pharmacist if you’re unsure about the right dose. Ibuprofen should not be given to babies under 6 months old.
Beyond medication, keep your child in light, comfortable clothing. Bundling them up can actually trap heat and push their temperature higher. Offer extra fluids throughout the day, since fevers increase fluid loss. Let them rest. Skip rubbing alcohol baths or ice water, which can cause shivering and paradoxically raise core temperature.
Warning Signs Beyond the Number
The temperature alone doesn’t tell you how sick your child is. A child with a 103°F fever who’s drinking fluids and playing between naps is generally in better shape than a child with 101°F who’s limp and unresponsive. Pay attention to behavior more than the thermometer.
Seek immediate medical care if your child has a fever along with any of these:
- Extreme lethargy or unresponsiveness: difficulty waking up or no interest in interacting
- Difficulty breathing: rapid breathing, flaring nostrils, or visible rib pulling with each breath
- Seizures: even brief ones
- Signs of dehydration: dry or cracked lips, no tears when crying, fewer than six wet diapers in 24 hours, or a sunken soft spot on a baby’s head
- A rash that doesn’t fade when pressed or purple spots on the skin
- Stiff neck: resistance to bending the head forward
- Persistent, inconsolable crying or an unusual high-pitched cry
- A fever lasting more than five days, even if it’s low-grade
Children with weakened immune systems (from medications, chronic illness, or recent surgery) should be evaluated for any fever at or above 100.4°F, since their bodies may not mount a strong enough response to fight infections on their own.