Health & Safety

What temperature is a fever in a baby?

Q: What temperature is a fever in a baby?

38°C or above is a fever. In a baby under 3 months, 38°C+ needs same-day medical advice (call 111 or your GP); under 6 months, 39°C+ does. For older babies, behaviour matters as much as the number — a floppy, unresponsive or persistently distressed child needs help regardless of the thermometer. Trust your instincts and seek advice.

The age-based thresholds

Under 3 months with 38°C+: contact a doctor or 111 the same day, even if baby seems otherwise well — young babies can't localise infection the way older children can, so fever alone earns a check.
3–6 months with 39°C+: same-day advice, same reasoning.
Older babies: the number matters less than the child. Fever is the immune system working; how they look and behave between spikes is the better signal.

Measuring properly

A digital thermometer in the armpit is the NHS-recommended method under 5 (forehead strips are unreliable; ear thermometers are fine used correctly on older babies). Don't measure straight after a bath or feed.

Red flags at any temperature

Call 999 or go to A&E if a feverish child is floppy or unresponsive, has a rash that doesn't fade under a pressed glass, struggles to breathe, has a fit, or can't be woken. Call 111 or your GP if a fever lasts more than 5 days, they're refusing all fluids with fewer wet nappies, or they're persistently distressed and you're worried. On instinct: parents who "just feel something's wrong" are right often enough that every NHS pathway tells you to act on it.

Health answers describe NHS guidance and are not medical advice — for anything urgent, call 111 (or 999 in an emergency). Spotted something out of date? Email editors@clevermum.co.uk.