TempoLife › Features › Fever and childrens medicine dosing by weight › what-counts
What counts as a fever at each age
The measurement thresholds, why the site matters, and the one age where any fever is urgent.
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.
The thresholds
A fever is a core temperature of 38 °C or more. Rectal measurement is the reference; an axillary (armpit) reading runs about half a degree lower, so 37.5 °C under the arm corresponds to a core fever, and ear and forehead thermometers have their own tolerances. The number that matters is the measured site plus the method, which is why the measuring page says which site to use at which age.
The one age where any fever is urgent
In a baby under three months, any measured fever — even 38.0 °C — is an urgent medical matter, not a home-care matter, because the immune system is immature and serious infection can present with almost nothing else. The rule is not "wait and see" but "call now". Between three and six months the bar relaxes but not by much: any fever above 38.5 °C, or any fever with poor feeding, drowsiness or a rash, still means a call.
Why fever exists
Fever is not the disease; it is the thermostat. The hypothalamus raises the body's temperature set-point in response to infection, and the higher temperature makes the immune response work faster while slowing some pathogens. The fever itself is usually harmless — even a high-looking 40 °C in an otherwise well child — which is why the treatment target is the child's comfort, not the number on the thermometer.
When the number does matter
The number matters when it comes with the child: a child who is alert, drinking and only mildly bothered at 39.5 °C is less concerning than a listless, poorly drinking child at 38.2 °C. The red-flag page lists the combinations that override everything else on this page.
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
Is 37.5 °C a fever?
Measured in the armpit, 37.5 °C corresponds to a core fever, because the axillary site runs about half a degree below the core. Measured rectally it is normal. The site and the method are part of the number.
How high is too high?
There is no single dangerous number in an otherwise well child; 40 °C looks alarming and is usually tolerated fine. The dangerous combinations are fever with drowsiness, poor drinking, a rash that does not fade under a glass, breathing trouble or a stiff neck — the red-flag list.
Should I wake a sleeping child to check the temperature?
No. Sleep is the body working; a child who can sleep does not need to be woken for a number. Check when they wake, and watch the behaviour rather than the thermometer.
The rest of the fever pages
Fever at every age
All seven fever pages, with the thresholds, the ladders and the red flags.
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.
A medicine log that answers the call
TempoLife timestamps every dose so the daily ceilings stay visible and the doctor gets exact numbers instead of a guess.