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Fever in children, by weight and by age
What counts as a fever at each age, the weight-based paracetamol and ibuprofen tables with the daily ceilings, how to look after a feverish child, and the red flags that mean call now instead of waiting.
This is a reference, not a prescriber: the package insert of the bottle in your hand outranks every number on this page, aspirin is never for children, and in a baby under three months any measured fever is urgent — call now, do not dose. If the child is on other medicines, or has a known liver, kidney or stomach condition, dosing belongs to a clinician.
How to read this
Fever in children is mostly a numbers problem with one twist: the numbers are weight-based, not age-based, and the dangerous part is usually the dosing errors and the missed red flags rather than the temperature itself. The seven pages below follow the order a worried parent actually needs them: is it a fever, how do I measure it, how much of each medicine, when is it not a home case, how do I look after them, and what if they seize.
What counts as a fever at each age
The measurement thresholds, why the site matters, and the one age where any fever is urgent.
Measuring temperature: which thermometer at which age
Rectal is the reference, the armpit is the compromise, and the ear is only as good as its aim.
Paracetamol dosing by weight
15 mg per kilogram per dose, every 4–6 hours, four doses a day at most — with the arithmetic worked.
Ibuprofen dosing by weight
10 mg per kilogram per dose, every 6–8 hours, from 3 months and about 5 kg — and the situations where it is the wrong choice.
When to call instead of waiting
The red flags that override the thermometer — by age, and the combinations that are always urgent.
Looking after a feverish child
Fluids first, comfort second, medicine for comfort rather than the number, and the two things that make it worse.
Febrile seizures: what they look like and what to do
A fever-driven seizure looks terrifying and is almost always brief and harmless — here is the protocol and the exceptions.
The two rules that prevent nearly every dosing error
First: the dose is the child's weight, not the child's age. Two children of the same age can differ by half in weight, and every paediatric formulation prints a weight ladder for exactly that reason. Second: the daily ceilings are as much a rule as the single doses — four paracetamol doses a day at most, three ibuprofen doses a day at most — and the classic overdose is stacking two products that both contain paracetamol. Read the ingredient list of everything given.
And the one rule that overrides both: in a baby under three months, any measured fever is urgent, and the treatment is a call, not a dose.
Fever thresholds and red flags: the national paediatric guidance in the region. Dosing: the standard weight-based rules — paracetamol 15 mg/kg per dose every 4–6 hours, at most four doses a day (60 mg/kg/day ceiling); ibuprofen 10 mg/kg per dose every 6–8 hours, at most three doses a day (30 mg/kg/day ceiling), from 3 months and about 5 kg. Febrile seizures: the standard paediatric emergency guidance (simple vs complex, the five-minute line). Checked 2026-09-06.
Frequently asked questions
What counts as a fever?
A core temperature of 38 °C or more, with the measurement site as part of the number — an armpit reading runs about half a degree below the core, so 37.5 °C under the arm is a core fever. Rectal measurement is the reference, and it is the only site reliable enough for the under-three-month rule.
How much paracetamol do I give a child?
By weight, not age: 15 mg per kilogram per dose, every 4 to 6 hours, and never more than four doses in 24 hours — a 60 mg/kg daily ceiling. A 10 kg child gets 150 mg per dose. Read the ingredient list of everything you give, because the classic overdose is two paracetamol products stacked.
How much ibuprofen do I give a child?
10 mg per kilogram per dose, every 6 to 8 hours, at most three doses a day — a 30 mg/kg daily ceiling — from 3 months of age and about 5 kg of weight. Give it with food or milk. Ibuprofen is avoided in chickenpox and in a dehydrated child, and aspirin is never for children with a fever.
When should I call instead of treating at home?
Under three months, any measured fever: call now. Three to six months, any fever above 38.5 °C or any fever with poor feeding, drowsiness or a rash. Any age: a fever past three full days, or any of the urgent combinations — the rash that does not fade under a glass, the stiff neck, breathing trouble, a seizure, or a child who cannot be roused.
Should I treat the fever or the child?
The child. Fever is the immune system working and is not dangerous at ordinary heights; the medicine is for the child's comfort, at the weight-based dose, when the fever is costing them comfort. Fluids matter more than the number on the thermometer.
Log the numbers, not the panic
TempoLife keeps a symptom and medicine log with timestamps, so the doctor's four questions — age, weight, readings, medicines given — are already answered when you call.