The short answer: for a baby under 4 weeks old, use a digital thermometer under the arm. That's what NICE recommends, and the NHS says to use the armpit for all children under 5. From 4 weeks, NICE also accepts an infrared ear thermometer. Skip forehead strips and old glass mercury thermometers, and don't use the mouth or bottom.
The NHS says a high temperature is 38C or more, and to call 111 if your baby is under 3 months with 38C or higher, or 3 to 6 months with 39C or higher. But how your child seems matters more than the number. This guide sums up NHS and NICE advice; it isn't medical advice.
What thermometer is best for a newborn (and after 4 weeks)?
NICE's fever guideline, written for health professionals, sets out the method by age:
| Age | What NICE recommends |
|---|---|
| Under 4 weeks | An electronic (digital) thermometer under the arm |
| 4 weeks to 5 years | An electronic or chemical dot thermometer under the arm, or an infrared ear thermometer |
| Not recommended | The mouth or bottom as a routine for under 5s, and forehead chemical strips |
The NHS keeps it simpler: a digital thermometer in the armpit for every child under 5. So a digital stick is right at any age.
Ear or forehead thermometer for a baby?
Ear thermometers are on NICE's list from 4 weeks. They're quick, but the NHS warns they can mislead if they aren't put in the ear correctly, which is more likely with a baby's small ear.
Forehead strips show the temperature of the skin rather than the body. The NHS says they aren't accurate, and NICE calls them unreliable.
Infrared no-touch forehead thermometers are a different thing, but to be plain: they aren't on NICE's list for under 5s, and the NHS page on taking your baby's temperature doesn't mention them. So treat one as a quick check, lovely for a sleeping toddler you don't want to wake. If it reads high, or doesn't match how your child seems, confirm it under the arm (or in the ear, from 4 weeks) before you act on it.
How to take a baby's temperature under the arm
This is the NHS method, and it works with any digital stick:
- Sit your baby comfortably on your knee and put the tip of the thermometer into the top of their armpit.
- Gently but firmly hold their arm against their side for as long as the instructions say, usually about 15 seconds. Many beep when they're done.
- Read the display.
Tight wrapping, a warm room, a hot water bottle, heavy clothes, a bath or lots of activity can nudge the reading up. If so, let your baby cool down for a few minutes (without getting cold or shivery) and take it again.
How to use an ear thermometer properly
Technique matters more here, so follow your model's instructions. Braun's ThermoScan instructions make a good template:
- Fit a fresh lens filter every time, and choose the age setting if there is one.
- Fit the probe snugly into the ear canal, pointing towards the opposite temple, then press start and hold it steady until it confirms the reading.
- Use the same ear each time, because left and right can read differently.
- If they've been lying on their side, use the ear that was facing up, and avoid an ear with lots of earwax or ear drops in it.
If an ear reading surprises you, take it again, or check under the arm.
What counts as a high temperature in a baby?
The NHS says a normal temperature in babies and children is about 36.4C, though it varies a little, and a high temperature is 38C or more. Your baby might feel hotter than usual on their back or chest, be sweaty or clammy, or have flushed cheeks.
Age changes what a number means. NICE puts babies under 3 months with 38C or higher in a high-risk group for serious illness, and babies of 3 to 6 months with 39C or higher in at least an intermediate-risk group.
One catch: Braun's Age Precision colours are Braun's own bands, not the NHS thresholds. On the ThermoScan 7+, the 3 to 36 months setting stays yellow up to 38.5C, while the NHS counts 38C as high. Go by the NHS numbers.
How your child seems matters more than the number
NICE tells doctors not to judge how ill a child over 6 months is from the height of their temperature alone, and not to judge any child by whether it comes down after paracetamol or ibuprofen. Are they feeding? Responding to you like they normally do? Unusually drowsy? That's the bigger picture. NICE also says a parent's sense that their child has a fever should be taken seriously, so trust your instincts.
Which thermometer should I buy?
You don't need to spend much. Based on our baby thermometer reviews:
- Before the birth: a digital stick. Our Value Star, the Braun Age Precision Digital Stick (around £12), does what NICE recommends for newborns, with no covers to buy. Keep it under the arm.
- From 4 weeks, for speed: an ear thermometer. Our Gold Star, the Braun ThermoScan 7+ (around £45), is quick and has a night mode. Most families end up with both: ThermoScan 7+ vs the digital stick.
- On a tighter budget: the ThermoScan 3 (around £20) is just as quick but has no night mode or colour coding. Is the 7+ worth the extra?
- If you'd use an app: the ThermoScan 7+ connect (around £50) logs each reading with the time. See ThermoScan 7+ vs 7+ connect.
- A no-touch extra for night checks: the Braun Sensian 7 (around £33) is our Best no-touch pick, ahead of the Tommee Tippee No Touch (around £30): Sensian 7 vs Tommee Tippee. Torn between ear and forehead? ThermoScan 7+ vs Sensian 7. Make it your second thermometer, not your only one.
When to get help
A high temperature usually goes down within 1 to 4 days, and you can usually look after your child at home. Here's when to get help, in the NHS's words.
Call 111, or ask for an urgent GP appointment, if your child:
- is under 3 months old and has a temperature of 38C or higher, or you think they have a high temperature
- is 3 to 6 months old and has a temperature of 39C or higher, or you think they have a high temperature
- has other signs of illness, such as a rash, as well as a high temperature
- has had a high temperature for 5 days or more
- does not want to eat, or is not their usual self and you're worried
- is dehydrated, such as nappies that are not very wet, sunken eyes, or no tears when crying
Call 999 if your child:
- has a stiff neck, is bothered by light, or has a fit for the first time
- has a rash that does not fade when you press a glass against it
- has unusually cold hands and feet, or blue, grey, paler than usual or blotchy skin, lips or tongue
- is drowsy and hard to wake, extremely agitated (does not stop crying) or confused
- has difficulty breathing, such as grunting, breathing very fast or their tummy sucking in under their ribs
- is not responding like they normally do, or is not interested in feeding or normal activities
And if you're worried, whatever the thermometer says, pick up the phone. A thermometer helps you describe what's happening. It doesn't make the decision for you.