A high temperature, or fever, in a baby is 38°C or above. But the number is only part of the picture: your baby's age and how they seem in themselves are important too.
If you are worried that your baby feels hot, check their temperature with a digital thermometer rather than relying only on touch.
What counts as a high temperature in a baby?
The NHS considers 38°C or above to be a high temperature in babies and children.
A baby's normal temperature can vary slightly. Feeling your baby's chest or back may make you notice that they seem warmer than usual, but a thermometer gives you a much more useful reading.
For guidance on choosing and using one, see choosing the best thermometer for a newborn
When is a baby's temperature urgent?
Age matters. If your baby is under 3 months old and has a temperature of 38°C or higher, the NHS advises seeking urgent medical advice.
For babies aged 3 to 6 months, the NHS advises seeking urgent medical advice if the temperature is 39°C or higher, unless they have had a vaccination in the previous 2 days.
There are other warning signs that may need urgent or emergency help regardless of the temperature, including difficulty breathing, unusual drowsiness or being hard to wake, a seizure, or blue, grey, pale or blotchy skin, lips or tongue.
If you think your baby is seriously unwell, trust your judgement and seek medical help.
How should you take a baby's temperature?
For children under 5, the NHS recommends using a digital thermometer in the armpit.
Place the thermometer in the top of the armpit, gently hold your baby's arm against their body and leave it in place for the time stated in the manufacturer's instructions.
What if my baby has a fever at night?
You do not need to wait until morning if you are worried. NHS 111 can advise you when you need medical help but it is not a life-threatening emergency. Call 999 for an emergency.
For more information, see what to do if your baby gets ill at night.
Should you give medicine for a fever?
Paracetamol or ibuprofen may sometimes be suitable if a baby or child is distressed or uncomfortable, but age, weight and individual circumstances matter.
Do not use medicine as a reason to delay getting medical advice for a young baby with a temperature that meets an urgent-help threshold.
For more detail, see when babies can have paracetamol and when babies can have ibuprofen
It helps to be prepared
Keeping a digital thermometer somewhere easy to find, knowing how to use it and having NHS 111 and your GP details saved can make an unsettling moment a little easier to manage.
For a broader checklist, see the baby medicine cabinet checklist