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What temperature counts as a fever in a baby?

A rectal temperature of 38.0°C (100.4°F) or higher is considered a fever in babies, and this is the most accurate way to check.

Any baby under 3 months with a rectal temperature at or above this level needs prompt medical assessment, even if they seem well.

Strength of evidence

Strong

Based on national pediatric guidelines and position statements from the Canadian Paediatric Society and American Academy of Pediatrics, which agree on this threshold.

What the evidence says

For babies, a fever is defined as a rectal temperature of 38.0°C (100.4°F) or higher. This is considered the gold-standard, most accurate way to check a baby's temperature, especially for infants under 3 months old.

Other methods (oral, ear/tympanic, forehead) are less accurate in babies, and armpit (axillary) readings tend to run a bit lower, so they may miss a true fever. If an armpit reading is normal but your baby feels warm and seems unwell, it's worth confirming with a rectal reading.

The age of your baby matters a lot when deciding what to do about a fever. Babies younger than 3 months with a rectal temperature of 38.0°C or higher should be seen by a doctor urgently, even if they seem otherwise well, because young infants can get seriously ill quickly. Babies 3 to 6 months old with a fever should also be checked by a doctor.

For babies over 6 months who otherwise seem well, fed, and comfortable, a fever itself is not dangerous and doesn't always need treatment - it's a normal sign the body is fighting an infection.

Sources

  • Guideline Management of well-appearing febrile young infants aged ≤90 days Canadian Paediatric Society (cps.ca), 2023

    Canadian guideline defining fever as rectal temp ≥38.0°C in young infants

  • Guideline Fever and temperature taking Caring for Kids, Canadian Paediatric Society, 2020

    Canadian guidance on fever thresholds, thermometer methods, and when to see a doctor by age

  • Guideline Fever and Your Baby HealthyChildren.org (American Academy of Pediatrics), 2023

    Defines rectal temp ≥38.0°C (100.4°F) as fever; details by age

  • Guideline Infant Fever American Academy of Pediatrics (aap.org), 2021

    AAP clinical practice guideline threshold for infants 8-60 days old

  • Guideline Fever in children Royal Children's Hospital Melbourne (rch.org.au), 2023

    Confirms 38°C threshold and urgent care for babies under 3 months

  • Guideline High temperature or fever in children Raising Children Network (Australian government funded), 2023

    Defines normal range and 38°C fever cutoff

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked July 29, 2026

Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so this may not apply to you. In an emergency, call your local emergency number. What Founded Parent cannot do

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