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Health · 0-12 months

Baby fever: when to call the doctor

Checked against current guidance on October 8, 2026. General information, not medical advice.

Illustration of a parent checking a baby's temperature with a digital thermometer.

The 10-second answer

  • Under 3 months: 38°C or higher needs medical advice right away, even if your baby seems well.1234
  • 3-6 months: the AAP says call the doctor at 38.3°C or higher, the NHS at 39°C or higher. Call at any temperature if your baby seems unwell.13
  • Below 36°C is too cold for a baby. Check again twice within 10 minutes; if it stays below 36°C, call your local emergency number or go to an emergency department.679
  • From 6 months, how your baby looks and acts matters more than the number. Under 3 months, the number alone is reason to call.4

General information from published guidance, not a diagnosis or medical advice for your baby. If you are worried, call your doctor, midwife or local health line, whatever this page says. In an emergency, call your local emergency number.

Fever thresholds by age: what the guidance says

Pick your baby's age to see the temperatures at which the AAP (US) and the NHS (UK) say to call a doctor. This is the published guidance, not an assessment of your baby. If your baby seems unwell, call, whatever the number.

Choose by birthday
AAP (US) says call at
38°C or higher
NHS (UK) says call at
38°C or higher
What to do
Call your doctor right away, even if your baby seems well (in the UK, call 111, or 999 if your baby seems very unwell).

In the US the AAP recommends a rectal reading at this age. In the UK the NHS and NICE recommend under the arm. Follow the method your own doctor recommends.12345

AAP (US) says call at
38.3°C or higher
NHS (UK) says call at
39°C or higher
What to do
Call your doctor the same day (in the UK, call 111, or 999 if your baby seems very unwell). Call at any temperature if your baby seems unwell.

Offer plenty of feeds and dress your baby in light clothing while you wait.1234

AAP (US) says call at
39.4°C or higher
NHS (UK) says call at
No single number: how your baby is matters most
What to do
Call your doctor if a fever lasts more than 24 hours, keeps coming back, or your baby seems unwell.

At this age, how your baby looks and behaves matters more than the number.123

Note the temperature in Ella with the time, so everyone at home knows. Open Ella

Get medical help now if

  • your baby is under 3 months with a temperature of 38°C or higher1234
  • your baby is floppy, very sleepy or hard to wake347
  • breathing is fast, noisy or hard work, or the lips look blue or grey347
  • there is a rash that does not fade under a pressed glass347
  • your baby has a seizure, or the soft spot is bulging2347
  • your baby is feeding much less or has fewer wet diapers (in the UK, call 111)349

Call your doctor or midwife today if

  • your baby is 3-6 months old with a temperature of 38.3°C or higher (call the same day)1
  • a fever lasts more than 24 hours2
  • your baby seems unwell to you, whatever the number says24

If your baby stops breathing, turns blue or grey, is floppy or cannot be woken, call your local emergency number now.

The details

How to take a baby's temperature

Guidance differs by country.

  • US (AAP): for babies under 3 months, a digital rectal reading is the most accurate. Put a little petroleum jelly on the tip and insert it gently about 1.3 cm. Stop if you feel resistance.
  • UK (NHS and NICE): use a digital thermometer under the arm. NICE advises against routine rectal readings in young children.
  • Forehead and ear: handy for quick checks. The AAP advises against ear thermometers under 6 months; NICE allows infrared ear thermometers from 4 weeks.
Follow the method your own doctor or health service recommends. Never use a glass mercury thermometer.

1345

Why under 3 months is different

Young babies can't fight infections as well, and a fever may be the only early sign of a serious one. That is why every guideline says a temperature of 38°C or higher before 3 months needs a doctor's assessment, even if the baby seems fine.

134

Keeping your baby comfortable

Offer extra breast or bottle feeds, dress your baby in light clothing and keep the room at a comfortable temperature. Don't bundle a baby with a fever, and don't sponge them with cold water. Don't give fever medicine to a baby under 3 months unless a doctor or nurse tells you to (in the UK, nurses advise paracetamol after some routine baby vaccinations: follow their instructions), and never give aspirin to babies or children.

348

Fever after vaccines

A mild fever is common after vaccinations. If your baby is under 3 months, call your doctor or nurse for advice about any temperature of 38°C or higher, even after vaccines. At any age, call your doctor straight away if your baby seems unwell or the temperature is 39°C or higher, and call if the fever lasts more than 24 hours.

248

Warm to the touch is not a fever

Babies can feel hot after a feed, in a warm room or when they are overdressed. Take off a layer, wait 15-30 minutes, and measure with a thermometer before deciding.

13

Questions parents ask

What temperature is a fever in a baby?

38°C or higher is a fever. Under 3 months, that number alone is a reason to get medical advice right away.1345

Is 37.5°C (99.5°F) a fever in a baby?

No. It is at the top of the normal range. Remove a layer, offer a feed and check again in 30 minutes.36

Does teething cause a fever?

Teething can make a baby slightly warm, but it does not cause a fever of 38°C or more. Look for another cause and call your doctor if you are unsure.1

Are forehead thermometers accurate for babies?

They are handy for a quick check. Guidance differs by country: in the US, the AAP says a digital rectal reading is the most accurate for babies under 3 months; in the UK, the NHS and NICE recommend a digital thermometer under the arm. Follow your own doctor's advice.1534

Should I wake my baby to check their temperature?

If your baby has a fever and you are worried, yes: check how they wake and respond. A baby who is very hard to wake needs help now.347

Ella

Have the answers the doctor will ask for

When did your baby last feed? How many wet diapers today? Ella has it on every family phone, and on Android you can create a PDF summary to bring to the check-up.

Start your free journalHow Ella tracks this

Sources

  1. AAP, HealthyChildren.org: Fever and your baby
  2. AAP, HealthyChildren.org: When to call the pediatrician about a fever
  3. NHS: High temperature (fever) in children
  4. NICE guideline NG143: Fever in under 5s
  5. AAP, HealthyChildren.org: How to take a child's temperature
  6. WHO: Thermal protection of the newborn: a practical guide (1997)
  7. NHS: Sepsis (symptoms in babies and children)
  8. UKHSA (GOV.UK): What to expect after vaccinations
  9. NHS: When to get urgent medical help for babies and children under 5

Guidance can differ between countries. Where it does, we show both. Follow your own doctor or health service.

Checked against current guidance on October 8, 2026. General information, not medical advice. Written by the Ella team at Muchita AI from published guidance by the AAP, NHS, NICE, WHO and CDC, with AI-assisted drafting and translation checked against those sources by our team. These organisations have not reviewed or endorsed this page. General information, not a diagnosis or medical advice. If you are worried about your baby, trust your instinct and call a doctor.

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