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What fever is too high for a 3- to 6-month-old?

For a baby of 3 to 6 months, a temperature of 102.2 °F (39 °C) or higher means call your pediatrician right away. The NHS fever page gives that threshold for this age; the AAP's lower threshold of 100.4 °F (38 °C) applies to babies under 3 months.

Call your pediatrician right away (UK: your GP or NHS 111) if your baby:

  • 3 to 6 months, 39 °C (102.2 °F) or higher
Fever thresholds by age
AgeTemperatureActionSource
3 to 6 months39 °C (102.2 °F) or higherCall your pediatrician right away (UK: 111 or your GP)NHS
Under 3 months (12 weeks)100.4 °F (38.0 °C) or higherCall your pediatrician right awayAAP

What the sources say

is 3 to 6 months old and has a temperature of 39C or higher

NHS (UK)Fever in childrenPage date: January 3, 2024Checked on October 23, 2026

Is younger than 3 months (12 weeks) and has a temperature of 100.4°F (38.0°C) or higher

AAP / HealthyChildren.orgFever: When to Call the PediatricianPage date: December 2, 2022Checked on October 23, 2026

At 3 AM

Say the number as the thermometer showed it and how you took it. 102.2 °F is 39 °C; if your thermometer reads in the other unit, give that reading and let them convert.

The threshold moves with age, so settle first which band the baby is in. At 3 months and a day, the 39 °C line applies; the day before, it was 38 °C. If the baby was born early, say so and give the due date as well, and let the clinician decide which line to use.

A reading below the line is not an all-clear. The other signs on this site do not depend on the thermometer: a baby who is hard to wake, breathing differently, not feeding for 8 hours, or not wetting diapers needs a call whatever the number says.

Have these ready: the baby's age in weeks, the temperature and method, when it started, what you have given and when, feeds and wet diapers in the last 24 hours, and how the baby is behaving between readings.

Log each reading with its time. Two readings an hour apart say more than one, and a log is quicker to read out than a memory at 3 AM.

Where the sources differ

The AAP page in our list gives a threshold only for babies under 3 months. The NHS gives one for 3 to 6 months as well. This page uses the NHS line for this age band and the AAP line for the younger one, and points at the stricter action wherever they disagree.

You know your baby best. If you think something is seriously wrong, get help now.

This page is general information, not medical advice. If you're worried, call your pediatrician.

Both fever lines sit on the free When to call a doctor page in Baby Tracker for Dads, one tap from the log where you wrote the reading.

Written by The Baby Tracker for Dads teamChecked on October 23, 2026Medical review: pending. Every number on this page is quoted from the AAP, CDC or NHS; the links are above.