A fever in a newborn? Call first, read after.
The CDC, the American Academy of Pediatrics and the NHS each say what counts as a fever in a baby, how to take the temperature, and when to call. Here’s what they say, in their own words, with a link to every page.
When to call, by age
The sources don’t draw the age line in the same place, so here is each of them.
“Talk to a healthcare provider right away
If your child is under 3 months old with a fever of 100.4 °F (38 °C) or higher.” CDC
“If your baby is 3 months of age or younger and has a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, call your pediatrician immediately. This is very important, even if your baby shows no other signs or symptoms of being ill.” American Academy of Pediatrics
“Call Doctor or Seek Care Now ... Fever in baby less than 12 weeks old. Caution: do NOT give your baby any fever medicine before being seen. ... Contact Doctor Within 24 Hours
Age 3-6 months old with fever” AAP KidsDoc (Barton Schmitt, MD)
“Urgent advice: Call 111 if your child:
is under 3 months old and has a temperature of 38C or higher, or you think they have a high temperature
is 3 to 6 months old and has a temperature of 39C or higher, or you think they have a high temperature” NHS
“You also may need to notify the doctor if your child is between 3 and 6 months and has a fever of 101 degrees Fahrenheit (38.3 degrees Celsius) or greater, or is older than 6 months and has a temperature of 103 degrees Fahrenheit (39.4 degrees Celsius) or higher.” American Academy of Pediatrics
“Call your pediatrician right away if your child:
is 2 months old or younger with a rectal temperature of 100.4 degrees Fahrenheit or higher, or if fever rises above 104°F (40°C) repeatedly at any age.” American Academy of Pediatrics
“Babies younger than 6 months old should see a doctor when they have a fever. Babies younger than 3 months old should be seen urgently.” Canadian Paediatric Society
“If your child aged 0-3 months has a fever, seek immediate medical attention. For example, take your child to a GP or hospital emergency department.” Raising Children Network
What counts as a fever in a baby
“A normal temperature in babies and children can vary slightly from child to child.
A high temperature is 38C or more.” NHS
“A normal temperature in babies and children is about 36.4C, but this can vary slightly. A high temperature or fever is usually considered to be a temperature of 38C or above.” NHS
“Ordinarily, a rectal temperature reading of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher is considered a fever. A rectal reading is the most reliable and accurate for infants, especially babies under 3 months old.” American Academy of Pediatrics
“Your child has a true fever if:
Rectal (Bottom), Ear or Forehead temperature: 100.4° F (38.0° C) or higher
Oral (Mouth) temperature: 100° F (37.8° C) or higher
Under the arm (Armpit) temperature: 99° F (37.2° C) or higher
Caution: ear temperatures are not accurate before 6 months of age” AAP KidsDoc (Barton Schmitt, MD)
“Any temperature above this range is considered a fever.
Method | Normal temperature range
Rectum | 36.6°C to 37.9°C (97.9°F to 100.2°F)
Mouth | 35.5°C to 37.5°C (95.9°F to 99.5°F)
Armpit | 36.5°C to 37.5°C (97.8°F to 99.5°F)
Ear | 35.8°C to 37.9°C (96.4°F to 100.2°F)” Canadian Paediatric Society
“Fever in children is when their body temperature is higher than 38°C. A normal temperature range for children is 36.5°C-38°C.” Raising Children Network
“Many authorities use either 100° F (37.8 degrees Celsius) or 100.4° F (38.0 degrees Celsius) as a cut-off for fever, but this number can vary depending on factors such as the method of measurement and the age of the person.” CDC
How to take a baby’s temperature
This is where the sources disagree most: the AAP and the Canadian Paediatric Society prefer a rectal reading for babies, the NHS uses the armpit, and Raising Children advises against rectal.
“Rectal (in the anus) temperatures are the most accurate. Forehead temperatures are the next most accurate. Oral and ear temperatures are accurate if done properly. Armpit temperatures are the least accurate, but you can use this method to screen a child of any age.” American Academy of Pediatrics
“Taking a rectal temperature gives the best reading, especially for infants under 3 months of age. ... Turn the thermometer on and slide it 1/2 inch (for babies less than 6 months old) to 1 inch into the anus.” American Academy of Pediatrics
“Avoid using an ear thermometer for babies under 6 months old, since their ear canals are too small to allow an accurate reading.” American Academy of Pediatrics
“Age | Recommended method
Birth to 2 years | Most accurate: Rectum Alternative: Armpit” Canadian Paediatric Society
“Hold them comfortably on your knee and put the thermometer in their armpit – always use the thermometer in the armpit with children under 5 years.” NHS
“Although you can use a digital probe thermometer to take a rectal temperature reading, this isn’t recommended. It’s uncomfortable for your child, and there’s a risk that the tip of the thermometer could damage the lining of your child’s rectum.” Raising Children Network
The temperature and the dose, with the time.
When you call, they’ll ask what it was and when, and what you gave. Bundle of Joy logs the medicine and the dose free, and the temperature with Premium, on your phone and your partner’s.
Sources
- CDC: Ear Infection Basics (January 25, 2024)
- American Academy of Pediatrics: Fever and Your Baby (September 23, 2025)
- AAP KidsDoc (Barton Schmitt, MD): Fever
- NHS: High temperature (fever) in children (January 3, 2024)
- American Academy of Pediatrics: How to Take Your Child's Temperature (April 17, 2024)
- Canadian Paediatric Society: Fever and temperature taking (June 2022)
- Raising Children Network: High temperature or fever in children (April 22, 2025)
- NHS: How to take your baby's temperature (July 18, 2023)
- CDC: Caregivers of Infants and Young Children (September 18, 2024)
- Raising Children Network: How to take temperature in children (April 22, 2025)
Every quote on this page was checked against its source on . Not medical advice: for your baby, ask your pediatrician or health visitor.
More from the sources: Baby feeding chart · Newborn diaper chart · Newborn weight loss and gain · Average newborn weight · Newborn sleep · Tummy time · Bathing a newborn · Cluster feeding · Infant Tylenol and Motrin dosage · Newborn hiccups · Baby colic
What it was, and when.
Doses on both your phones, with who gave them.
