The exact temperature thresholds, red flag signs, and clinical decision framework for managing fever in babies and children from birth to 8 years — sourced from NHS and AAP guidelines.
It was 2am. A first-time mum had been checking her baby's temperature every twenty minutes. The thermometer read 38.3°C. She didn't know whether to call 111, go to A&E, or wait until morning. Nobody had ever told her the rule that makes this decision simple.
A fever is a temperature of 38°C (100.4°F) or above. That is the clinical threshold. Below that is normal variation — not a fever, not something to treat with medicine.
Most parents panic at anything over 37°C. That panic is understandable — but giving Calpol at 37.4°C means your baby gets medicine they do not need, and you lose the ability to track whether they are actually getting worse.
The NHS uses age as the primary risk factor for fever in babies. Here is the rule. No exceptions.
Under 3 months with any fever (38°C+) — call 999 or go to A&E immediately. Do not call 111 first. Do not wait. A young baby's immune system cannot fight serious infection the way an older child's can.
3 to 6 months with a fever — call 111 or your GP same day. This age group needs medical assessment, not home management.
6 months to 5 years with a fever over 39°C — call 111 or see your GP. If your child looks well, is drinking, and you can manage the discomfort with paracetamol, monitor closely. If anything changes, call immediately.
Always dose by your baby's current weight, not their age. The age guide on the packet is a rough estimate only. A heavier baby in a younger age bracket may need more. A lighter toddler may need less.
Never use a kitchen spoon. Use the measuring syringe that comes in the box. If you have lost it, ask your pharmacist — they are free. Never exceed 4 doses in 24 hours. Leave at least 4 hours between doses.
NHS Fever in children guidance · NICE CG160 Feverish illness in children under 5 · British National Formulary for Children (BNFc) · Reviewed April 2026.