KidyFever in a baby or toddler: call, or watch?
Enter the temperature, how long it has lasted, and how your child is doing: colour, how they react, eating, wet diapers, breathing. You get one of four answers, from "call 911" to "watch at home, and call if it is still there by this time".
How old is your child?
Under 3 months, any fever counts differently.
The fever: how high, and for how long?
A fever is 100.4°F (38°C) or higher. Under 3 months, only a real reading will do.
How is your child doing?
Tick anything that fits. Nothing ticked means none of these is happening. The signs come from the NICE traffic light table for children with a fever.
Call 911 (999 in the UK)
See a doctor now
Call your doctor today
Any vaccinations in the last two weeks?
A fever after shots follows its own timing, so the answer can be more precise.
Which visit? UK: 8, 12 and 16 weeks match the 2, 4 and 6 month rows.
When?
Your answer
Log each reading and each dose in KidyGrow as it happens, and "when did this start?" has an answer instead of a guess. A logged fever also counts toward the next Daily Brief, which takes the last 24 hours into account.
Get the app →How the checker decides
The UK's NICE guideline for fever in children under 5 sorts signs into a traffic light: green for low risk, amber for intermediate, red for high. Doctors use it, and so do the NHS 111 phone lines when they cannot see the child. The checker takes the part a parent can see at home and works through it in this order.
- Emergency signs. Trouble breathing or grunting, a seizure, a rash that does not fade under a glass, a child who does not wake, swollen lips, tongue or throat with trouble swallowing or talking, blue or grey skin, a stiff neck, weak, high-pitched or non-stop crying. Any of these means 911 (999 in the UK) (NHS).
- See a doctor now. Under 3 months with 100.4°F (38°C) or more (AAP), 3 to 6 months with 102.2°F (39°C) or more (NHS), a floppy child, a bulging soft spot, refusing all fluids or far fewer wet diapers, repeated vomiting.
- Call today. Paler than usual, less reaction or activity than usual, faster breathing, eating and drinking much less, shaking chills, a limb they will not use, a temperature above 104°F (40°C) at any age, or a fever that has lasted more than 24 hours under age 2 or more than 3 days from age 2 (AAP).
- Watch at home. None of the above. The checker tells you until when, and which signs would change the answer.
If there was a vaccination in the last two weeks, it also checks whether the timing fits the vaccine. That part has its own page: fever after vaccines checker.
The traffic light, in parent terms
| Green | Amber | Red | |
|---|---|---|---|
| Colour | Normal | Paler than usual | Pale, blotchy, grey or blue |
| Activity | Reacts, smiles, wakes easily, strong cry | Less reaction, no smile, hard to wake, less active | Does not wake or stay awake, weak or non-stop cry |
| Breathing | Normal | Faster, nostrils flaring | Grunting, ribs sucking in |
| Fluids | Moist mouth, usual wet diapers | Dry mouth, poor feeding, fewer wet diapers | |
| Other | 39°C at 3 to 6 months, fever 5 days or more, shaking chills, swollen or unused limb | 38°C under 3 months, rash that does not fade, bulging soft spot, stiff neck, seizure |
Adapted from the NICE NG143 traffic light table, leaving out the parts only a clinician can measure (pulse, oxygen, capillary refill). The checker is stricter than the table in two places: 39°C at 3 to 6 months counts as see-a-doctor-now, because the NHS lists it for 999/A&E, and duration uses the AAP's 24 hours under age 2. It has no single temperature line after 6 months except the AAP's above 104°F (40°C), because neither NICE nor the NHS uses one.
While you watch
- Offer drinks and feeds often. Fluids matter more than bringing the number down.
- Dress your child lightly and keep the room comfortable. No extra blankets to "sweat it out".
- Check the temperature again in a few hours and write down the time. Check the signs above again too.
- Fever medicine only at the dose your pediatrician or the package gives for your child's age and weight. It is for comfort; it does not change how serious the illness is.
help_outlineFAQ
When is a baby's fever an emergency?
Call 911 (999 in the UK) for trouble breathing or grunting, a seizure, a rash that does not fade when you press a glass on it, a child who does not wake or stay awake, swollen lips, tongue or throat with trouble swallowing or talking, blue or grey skin, or a stiff neck.
What temperature is too high for a baby?
Under 3 months, 100.4°F (38°C) or more is always a call. At 3 to 6 months, 102.2°F (39°C) or more needs a doctor now. At any age, a temperature above 104°F (40°C), especially one that keeps coming back, is a reason to call (AAP). Above those lines, how your child looks matters more than the number.
How long can a fever last before I call the doctor?
The AAP says to call if a fever lasts more than 24 hours in a child under 2, or more than 3 days in a child 2 or older. After a vaccination the usual fever lasts one to two days.
Does eating and peeing matter with a fever?
Yes. Refusing all feeds or far fewer wet diapers can mean dehydration and needs a doctor now. Eating and drinking much less than usual is a reason for a doctor to see your child the same day.
Methodology
The warning signs are the ones a parent can see in the NICE NG143 traffic light table, sorted into three levels: the NHS list of emergency signs, the rest of the NICE red column plus dehydration as "see a doctor now", and the NICE amber column as "call today". Temperature and duration lines are the AAP's, with the NHS 102.2°F (39°C) line for 3 to 6 months as see-a-doctor-now. The vaccine step uses the CDC Pink Book and UKHSA timing windows.
Last reviewed: September 2026.
Sources
- NICE NG143: Fever in under 5s, traffic light table
- AAP, HealthyChildren.org: Fever, when to call the pediatrician
- NHS: High temperature (fever) in children
- CDC Pink Book: Measles (MMR fever timing)
Informational only, not a substitute for a doctor's assessment.