Baby Fever Guide — What's Normal, When to Worry, What Actually Helps

Few things rattle a parent like a hot, floppy little body in your arms at 2am. The good news: in babies over 3 months, fever itself is rarely dangerous — it''s a sign the immune system is doing its job. What matters is how your baby is behaving , not the number on the thermometer. This guide walks you through what counts as a real fever, how to measure temperature accurately, the red flags that mean call now, safe pain-relief dosing, and the comfort measures that genuinely help. Written from a Maternal Health Nurse lens, aligned with Red Nose, NHS and Royal Children''s Hospital Melbourne guidance. What counts as a fever? A normal body temperature for babies and children sits between 36.5°C and 37.5°C. A fever is generally defined as 38°C or higher when taken under the arm or in the ear. Forehead temporal thermometers can be a quick screen but are less reliable, especially in newborns. Low-grade fever: 38.0°C – 38.9°C Moderate fever: 39.0°C – 39.9°C High fever: 40°C or above The height of the fever doesn''t reliably tell you how sick your baby is. A baby with 38.2°C who is floppy and hard to rouse needs urgent attention; a toddler with 39.8°C who is still drinking, weeing and playing in flashes is usually fighting a routine viral illness. How to take your baby''s temperature accurately Method matters more than most parents realise: Under-arm axillary : the recommended method for babies under 3 months. Hold the thermometer snug against bare skin for the full reading time. Ear tympanic : reliable from around 6 months. Gently pull the ear back and up to straighten the canal. Forehead infrared : convenient but easily affected by sweat, room temperature and technique. Use as a screen, then confirm with under-arm if it reads high. Mercury / glass thermometers: avoid — they''re no longer recommended. Re-check 20–30 minutes after a bath, breastfeed or being heavily wrapped — all can falsely elevate readings. When fever is urgent — call now Call your GP, 13 HEALTH 1737 in NZ or 000 / 111 / 911 immediately if your baby has any of these: Under 3 months old with a temperature of 38°C or higher — always assessed urgently, no exceptions. 3–6 months old with a fever of 39°C or higher. Fever lasting more than 48 hours without an obvious cause. A non-blanching rash doesn''t fade when you press a glass against it . Stiff neck, bulging fontanelle, severe headache or sensitivit…