Use our temperature calculator to find out if your temperature is high or low by age.
Enter your age and the reading on your thermometer to see your results.
What is the ideal body temperature range?
A normal body temperature is generally considered to be anywhere between 36.1°C and 37.4°C. Having a temperature outside of this range may happen due to a number of causes, such as an infection, exposure to extreme weather, problems with the body auto-regulating its own temperature, or inflammation in the body.
Does illness always cause a high temperature or fever?
It is also possible to have a serious infection and still have a normal temperature. This is especially true for more elderly people, who often tend to run a bit cooler than younger and middle-age adults anyway, and frequently aren’t able to produce a ‘fever response’ even during an infection1. For this reason, a change in the usual baseline temperature can be significant, especially in an older adult.
A temperature may also be normal earlier on in the stages of an infection, so a normal body temperature shouldn’t be taken as blanket reassurance that there isn’t something serious happening. If you or your loved one has symptoms that concern you, make sure you seek medical attention as you would do normally, even if a thermometer shows a normal temperature. Read on for what to do when a thermometer shows an abnormal reading.
How you should take your temperature by age
The National Institute of Health and Clinical Excellence has given the following guidelines when it comes to using thermometers when assessing for a fever in children2:
- Oral and rectal thermometers should not be used routinely for children under 5 years of age.
- Infants under 4 weeks old: ideally use an electronic thermometer in the armpit (axilla).
- Children age 4 weeks to 5 years should have one of the following used:
- Electronic thermometer in the armpit.
- Chemical dot thermometer in the armpit.
- Infra-red tympanic thermometer3
- ‘Forehead chemical thermometers are unreliable and should not be used by healthcare professionals.’
- ‘Reported parental perception of a fever should be considered valid and taken seriously by healthcare professionals.’
In addition to the above, an important factor to consider is whether the thermometer you are using has the required accreditations to be reliable. Here at Kinetik, all of our thermometers meet the necessary ISO clinical directives (and some are even used by the NHS) so you can have peace of mind that you can trust the reading you see.
What affects your temperature?
As briefly mentioned above, there are multiple factors that can influence someone’s body temperature4. We all know that a high temperature can happen due to an infection. There are other causes of a raised temperature besides this though, such as heatstroke, inflammation in the body, and medical conditions such as an overactive thyroid gland (hyperthyroidism). However, not all causes are due to something going wrong: it can be normal for a body temperature to rise in response to exercise of course, as well as after ovulating, and even in response to the time of the day (due to our circadian rhythm, we are typically all at our warmest in the late afternoon).
Similarly, a lower body temperature may be due to a range of causes. Some of the more concerning ones are: a severe infection that is damaging our body (sepsis), exposure to extreme cold (hypothermia) and an underactive thyroid gland (hypothyroidism). It is not uncommon for adults over 65y to tend to have a slightly cooler baseline body temperature compared to when they were younger. Again, body temperature can also fluctuate with activity level and time of day, typically being at it’s lowest point when we are asleep.
What temperature is a fever?
Usually a mild, or ‘low-grade’ fever is considered to be a temperature between 37.5°C – 37.9°C. While this can happen due to an infection, when considering the indicator of body temperature alone, it may be less significant than a ‘proper’ fever of 38.0°C or higher. Please see ‘What body temperature is a fever5’ for more information.
What are the symptoms of a fever (without a thermometer)?
This can vary from person to person. Symptoms may include:
- Feeling hot and sweaty
- Shivering (this is called rigors in the context of a fever)
- Feeling generally unwell or under the weather
- Reduced appetite
- Reduced energy levels
High temperature (fever) in children
If your child has a high temperature, pay attention to other signs that could also suggest they are unwell. What are their activity/energy levels like? Are they happily running and making plenty of noise, or just curled up on the couch? What is their fluid intake like? Have they drunk and wee’d normal amounts today? If not, get them a drink straight away as dehydration can make simple illnesses become much more dangerous. Do they have any other signs or symptoms that make you concerned? (See ‘When you should dial 999 or 111’ below.)
If they are under 3 months old with a fever, it is usually best to seek prompt medical attention, especially if their temperature is 38.0°C or higher. If they are 3 – 6 months old and have a temperature of 39.0°C or higher (or have any other potentially serious symptoms – see below), this is also concerning. For other age ranges, see below.
It isn’t always necessary to give medicine to reduce a fever, especially if the child seems to be tolerating it quite happily. There is some evidence suggesting that a fever might help our bodies fight off an infection faster6. Fevers themselves don’t tend to cause damage but if the child seems miserable, or is in too much discomfort to drink enough, then some Calpol can certainly be helpful (provided they are old enough)!
What is a low temperature?
Generally, 35.1°C – 36.0°C is considered to be a low temperature. 35.0°C or less is considered to be a very low temperature and is usually the cut off for hypothermia.
What are the symptoms of hypothermia?
Of course, the easy-to-guess symptoms are those that you might feel if you get stuck outside on a cold day without enough layers: feeling cold, shivering, extremities starting to look a bit pale or blue. However, things can get pretty serious when it comes to a severely low body temperature. The more extreme symptoms include: confusion, drowsiness, slurred speech, slowed breathing and even a coma. If you think that someone has hypothermia and they have any of these symptoms, dial 999 or take them to A&E now. (Note: babies with hypothermia may have different symptoms – they may look red or floppy and seem very sleepy and not want to feed.)
The NHS has a handy Do and Don’t guide when it comes to looking after someone with suspected hypothermia while waiting for the ambulance to arrive7:
Do’s and don’ts of hypothermia
- move the person indoors or somewhere sheltered as quickly as possible
- remove any wet clothing, wrap them in a blanket, sleeping bag or dry towel, making sure their head is covered
- give them a warm non-alcoholic drink and some sugary food like chocolate if they’re fully awake
- keep them awake by talking to them until help arrives
- make sure you or someone else stays with them
- do not use a hot bath, hot water bottle or heat lamp to warm them up
- do not rub their arms, legs, feet or hands
- do not give them alcohol to drink
When you should dial 999 or 111 for a high temperature
Dial 999 or attend A&E if any of the following apply:
- For Children: If your child appears very unwell, looks pale, blotchy or blue, is not responding normally to you, has difficulty staying awake, seems to be struggling with their breathing (e.g., breathing very quickly or noisily), has a rash that doesn’t fade under pressure, neck stiffness, light sensitivity, very cold hands and feet, a weak, high-pitched cry, is inconsolable, confused or appears to be having a seizure for the first time, please ring 999 or attend A&E immediately. For further advice, visit https://www.nhs.uk/conditions/fever-in-children/
- For Adults: If your temperature is 40.0 or higher and you are feeling unwell, or if you have a fever and are feeling drowsy, confused, lightheaded, faint or short of breath, if you have a new severe headache along with vomiting +/- non-fading rash +/- neck stiffness +/- light sensitivity +/- changes to your vision, or if you have other symptoms that you think may be life-threatening.
Contact your GP or ring 111 if any of the following apply:
- For Children: For any less severe but still concerning symptoms, such as a rash that fades under pressure, not playing or smiling like normal, not drinking enough, weeing less than normal, shaking and shivering with a high temperature, fever lasting 5 days, or if this is for a baby <3 months with a temperature of 38.0°C or higher, or age 3 – 6 months and their temperature is above 39.0°C, or if you have that parental instinct that something isn’t right, please contact your GP or ring NHS 111. For further advice, visit https://www.nhs.uk/conditions/fever-in-children/
- For Adults: If you are concerned that you have serious, but not life-threatening symptoms, such as possible dehydration that you aren’t able to get on top of (a sign of this is only passing small volumes of dark urine or being excessively thirsty), a new, severe pain in the body, a fever persisting 5 days, a history of recent travel overseas, or if you have any other medical conditions or take medicine that could make you susceptible to complications or to more severe infections (e.g., having an organ transplant, diabetes mellitus, a suppressed immune system, lung or kidney disease)9.
- Dean C. Norman, Fever in the Elderly, Clinical Infectious Diseases, Volume 31, Issue 1, July 2000, Pages 148–151, https://doi.org/10.1086/313896
- Rice P, Martin E, He JR, Frank M, DeTolla L, Hester L, O’Neill T, Manka C, Benjamin I, Nagarsekar A, Singh I, Hasday JD. Febrile-range hyperthermia augments neutrophil accumulation and enhances lung injury in experimental gram-negative bacterial pneumonia. J Immunol. 2005 Mar 15;174(6):3676-85. doi: 10.4049/jimmunol.174.6.3676. PMID: 15749906. https://www.jimmunol.org/content/174/6/3676.long