The short answer
- Normal: about 36.1 to 37.2°C (97 to 99°F) in adults. It varies through the day and between people.
- Fever: 38°C (100.4°F) or higher.
- High fever: about 39.4°C (103°F) and above in adults.
- Babies under 3 months: a temperature of 38°C (100.4°F) or more needs medical advice straight away, even if the baby seems well.
Temperature guide
| Reading | °C | °F |
|---|---|---|
| Low (possible hypothermia) | Below 35.0 | Below 95.0 |
| Normal range | 36.1 to 37.2 | 97.0 to 99.0 |
| Slightly raised | 37.3 to 37.9 | 99.1 to 100.3 |
| Fever | 38.0 and above | 100.4 and above |
| High fever (adults) | 39.4 and above | 103.0 and above |
Need to convert? See Celsius to Fahrenheit.
Why readings differ
Body temperature naturally changes through the day, by up to about 0.5°C (1°F): lowest in the early morning, highest in the late afternoon and evening. It also rises after exercise, hot drinks, a hot bath and around ovulation.
The type of thermometer matters too:
| Method | Compared with an oral reading |
|---|---|
| Rectal | About 0.3 to 0.6°C (0.5 to 1°F) higher |
| Ear | Similar or slightly higher |
| Oral (under the tongue) | Reference |
| Armpit | About 0.3 to 0.6°C (0.5 to 1°F) lower |
| Forehead (temporal artery) | Similar to oral, depends on the device |
Use the same method each time so you can compare readings.
How to take a temperature properly
- Wait 15 to 30 minutes after eating, drinking, exercise or a bath.
- Digital oral: place it under the tongue towards the back, close the lips, and wait for the beep.
- Armpit: place the tip in the middle of a dry armpit and hold the arm against the body until it beeps. This is the usual method for babies under 3 months at home.
- Ear: pull the ear gently back (and up in adults and older children) to straighten the ear canal before measuring.
- Forehead: follow the device's instructions exactly; sweat and moving the probe too fast give low readings.
- Do not use glass mercury thermometers; they can break and release mercury.
Caring for a fever at home
A fever is the body's way of fighting infection, often from a cold, flu or another virus. It is not dangerous in itself in otherwise healthy people. Our guide to cold, flu and COVID symptoms helps you tell them apart.
- Drink plenty of fluids. Fever increases fluid loss. Look for pale urine.
- Rest.
- Dress in light clothing and keep the room comfortably cool. Do not bundle up or use cold baths or ice; they cause shivering, which can raise temperature.
- Medicines for comfort: paracetamol (acetaminophen) or ibuprofen can ease aches and discomfort. Follow the dose on the pack for age and weight, and do not exceed the daily maximum.
- Never give aspirin to under-16s, because of the risk of Reye's syndrome, a rare but serious condition.
- Do not give ibuprofen to anyone dehydrated, or if a doctor or pharmacist has advised against it, for example in some kidney or stomach conditions.
When to get medical help
Babies and children
Get medical advice straight away if:
- a baby under 3 months has a temperature of 38°C (100.4°F) or higher
- a baby 3 to 6 months has a temperature of 39°C (102.2°F) or higher
- a child is unusually drowsy, floppy, hard to wake or will not stop crying
- a child has a rash that does not fade when you press a glass against it
- a child has difficulty breathing, signs of dehydration (few wet nappies, no tears, sunken soft spot), or a seizure
- the fever lasts more than 5 days
Adults
Seek urgent help if a fever comes with:
- a stiff neck, severe headache or sensitivity to light
- a rash that does not fade under pressure
- difficulty breathing or chest pain
- confusion, extreme drowsiness or a seizure
- persistent vomiting, or being unable to keep fluids down
See a doctor if:
- the fever lasts more than 3 days or keeps coming back
- your temperature is 39.4°C (103°F) or above and does not come down with medicine
- you have a weakened immune system (for example from chemotherapy), are pregnant, or have a long-term condition
- you have recently travelled to an area with malaria or other tropical infections
Low temperature
A temperature below 35°C (95°F) can be a sign of hypothermia, especially in older adults and babies in cold homes, and needs urgent medical attention.
Preventing infections
Many fevers in winter come from the flu and other respiratory viruses. Vaccination, handwashing and staying home when ill all help. See our flu season and vaccine guide.
Key takeaways
- A fever is 38°C (100.4°F) or higher; normal is about 36.1 to 37.2°C (97 to 99°F).
- Readings vary by time of day and thermometer type.
- Treat for comfort with fluids, rest and the right dose of paracetamol or ibuprofen.
- A baby under 3 months with a fever needs medical advice straight away.
This article is general information, not medical advice. If you are worried about a fever, contact a doctor, a nurse helpline or emergency services.