Everyday temperatures

Fever Temperature Chart: Adults & Children (°F and °C)

A fever starts at 100.4°F (38°C). This chart breaks down severity levels for adults and children and the warning signs that warrant a call to a doctor.

Last reviewed: 2026-07-17

Fever chart (adults and children over 3 months)

Common fever classification (oral-equivalent readings)
Reading (°F)	Reading (°C)	Classification
97.0–99.0°F	36.1–37.2°C	Normal
99.1–100.3°F	37.3–37.9°C	Elevated / low-grade
100.4–102.2°F	38.0–39.0°C	Fever
102.3–104.0°F	39.1–40.0°C	High fever
Above 104.0°F	Above 40.0°C	Very high - seek medical advice
Above 106.0°F	Above 41.1°C	Medical emergency (hyperpyrexia)

Babies are different

For infants under 3 months, any rectal temperature of 100.4°F (38°C) or higher is an immediate call-the-doctor situation - do not wait to see how the baby does. For babies 3–24 months, call if the fever reaches 102°F (38.9°C), lasts more than 24 hours, or comes with unusual drowsiness, poor feeding, rash, or trouble breathing.

When adults should seek care

Call a clinician if you have

A fever above 103°F (39.4°C)
Any fever lasting more than three days
Fever with stiff neck, severe headache, chest pain, shortness of breath, confusion, rash, or dehydration

Go to emergency care for a reading above 105°F (40.6°C).

Treating the number itself matters less than comfort: fluids, rest, and - if appropriate for you - acetaminophen or ibuprofen. Avoid aspirin for anyone under 18. This page is general information, not medical advice; when in doubt, call your doctor or local health line.

Taking a temperature that you can trust

Fever decisions ride on half a degree, so measurement technique matters:

Under 3 months: rectal readings only - they are the standard every threshold in this chart assumes for infants.
3 months to 4 years: rectal or temporal (forehead); ear thermometers work from about 6 months if positioned well.
4 years and up: oral works once a child can hold the probe under the tongue with a closed mouth.
Adults: any method, but stay consistent and wait 15 minutes after eating, drinking or exercise for oral readings.

Whichever method you use, our normal body temperature guide shows how each one reads relative to oral.

Three fever myths worth dropping

“The higher the fever, the sicker the child.” Not reliably. A miserable child at 101°F needs more attention than a playful one at 102.5°F. Behavior beats the number, except at the emergency thresholds.
“Fevers cause brain damage.” Ordinary fevers do not; the body caps them around 105-106°F. The dangerous territory is heat stroke, an external overheating problem, not illness fever.
“Teething causes real fevers.” Teething can nudge temperature up slightly, but anything at or above 100.4°F (38°C) should be treated as illness, not teeth.

Frequently asked questions

Can teething cause a fever?

Teething may raise temperature slightly, but not to true fever levels. A reading of 100.4°F (38°C) or higher means something else is going on and should be evaluated like any fever.

Should I wake a sleeping child to check or treat a fever?

Generally no - sleep helps recovery. Exceptions: infants under 3 months with any fever, a child who is hard to rouse, trouble breathing, or your doctor has given specific instructions.

What temperature is a fever in adults?

100.4°F (38°C) or higher measured orally. 103°F+ (39.4°C+) is high and worth a call to a clinician.

What fever is too high for a child?

Call a doctor for any infant under 3 months at 100.4°F+, for 102°F+ (38.9°C) in babies 3–24 months, or any fever with lethargy, rash, stiff neck, or breathing trouble.

Should I alternate acetaminophen and ibuprofen?

Some clinicians recommend it for stubborn fevers, but dosing errors are common - get explicit instructions from a pharmacist or doctor before alternating.