What is a normal body temperature? Why yours changes through the day

You feel a bit warm, so you reach for the thermometer. It says 37.2°C. Is that a fever? Should you worry? Australians search for it thousands of times a month, and the answer is more reassuring than you might think.

The short answer: healthdirect says a normal body temperature is usually 36.5°C to 37°C, and a fever is 38°C or higher. Your own normal can sit a little above or below that, and it moves through the day. So a reading like 37.2°C on its own is usually nothing to worry about. Here's what's normal, why it changes, when a temperature is worth acting on, and how the Thrive Health Band and the Thrive by Optihealth app can help you learn your own normal.

What counts as normal

There isn't one perfect number. Healthdirect gives a normal range of 36.5°C to 37°C, and says your temperature depends on:

your age
the time of day
how your temperature was taken
whether you're awake or asleep

The Better Health Channel puts normal at around 37°C, give or take a degree, and notes that this varies from person to person. In other words, 37°C is a useful guide, not a target you have to hit.

Why your temperature changes through the day

Your body clock runs your temperature on a daily cycle. The Sleep Health Foundation explains that body temperature rises and falls over roughly 24 hours, and that core temperature is low at night, when melatonin is high. That's part of how your body gets ready for sleep. It's also why a cool bedroom helps. Our piece on warm nights and summer sleep covers that side.

Day to day, everyday things nudge it too. A brisk walk, a hot shower, a sauna, a warm room or a heavy doona can all leave you feeling warmer for a while. A cold morning or a swim can do the opposite. If you're training in warm weather, see exercising in the heat.

Where you take it matters

Thermometers can read your temperature in different places. Healthdirect lists the forehead, the ear, under the armpit and under the tongue. Each gives a slightly different number, so:

Follow the instructions for your thermometer.
Use the same type and the same spot each time if you're keeping track.
Wait a little after a hot drink, a shower or exercise before checking.
Keep the thermometer clean between uses.

What counts as a fever

Healthdirect defines a fever as 38°C or higher. A fever is usually part of your immune system responding to an infection, most often a virus such as a cold, flu or COVID-19. You might also notice sweating, shivering, aching muscles or a headache.

A mild fever isn't always a bad thing. The Better Health Channel notes that a mild fever up to 39°C can actually help your immune system clear an infection, and that most mild fevers settle on their own within a couple of days. If you're unwell with a cold, our guide to how long a cold lasts covers when to rest and when to get moving again.

Healthdirect's self-care tips for a fever are simple:

Drink plenty of clear, non-alcoholic fluids, such as water.
Dress lightly and skip the heavy blankets and doonas.
Keep the room at a comfortable temperature.
Avoid cold baths or sponging, which can make you shiver.
Rest, and avoid heavy activity until you feel better.

If you have aches as well, your pharmacist or GP can suggest over-the-counter pain relief that's safe for you.

And a low temperature?

A slightly low reading is usually down to how or when you measured it. A truly low body temperature is different. Healthdirect says hypothermia is when your temperature drops below 35°C and your body can't warm itself up. Symptoms can start with shivering and cool skin and move on to confusion, a slow heart rate and slow breathing. That's an emergency: call triple zero (000).

When to see your GP

Most temperature changes are your body doing its everyday job. A one-off reading a little above 37°C, with no other symptoms, is usually nothing to worry about. Even so, it's always fine to check in with your GP if you're unsure.

Healthdirect suggests seeing your doctor if a fever lasts more than 3 days and isn't getting better with self-care, or if you have any other symptoms you're concerned about. The Better Health Channel adds a temperature over 40°C, or feeling sicker as time goes on.

Go to your nearest emergency department straight away if a fever comes with seizures, confusion or difficulty breathing. For children, follow healthdirect's advice on fever in children, which explains when to call triple zero (000).

You can show your Thrive trends to your GP too. They can help you describe when you started to feel off and how your nights have been.

Get to know your own patterns

See your temperature trend. The Thrive Health Band estimates your temperature from your wrist through the day and night. It has no screen and up to 14 days of battery, so you can wear it to bed. Wrist temperature isn't the same number you'd get from a thermometer under your tongue, so treat it as an estimate and watch how it trends over time.

See it against general ranges. The Thrive by Optihealth app shows your temperature trend against general temperature ranges, as a general guide only. It isn't a diagnosis, and the Band is not a medical device. An estimate that sits higher than usual may simply reflect a warm room, a workout or the time of day. If you think you have a fever, use a thermometer, and talk to your GP if you're worried.

Log how you feel. "Fever", "Chills" and "Night sweats" are among the symptoms you can log in the app, with a note.

Add the context. In your Daily Check-In you can tag your day with things like Heat exposure, Cold exposure or Sauna, and rate your mood and stress. Thrive also shows your hours slept along with Quality, Quantity, Regularity and Timing, and your resting heart rate. See resting heart rate explained.

Over time, Thrive learns what's usual for you right across your health, from sleep, heart, temperature and activity to mood, stress, meals, medications and symptoms. Your Health Fingerprint is ready after about 30 days of wear. Then you can ask Ask Thrive questions like:

"How did my temperature trend the week I logged feeling unwell?"
"Does my temperature run warmer on days I tag Heat exposure?"
"How did my sleep change while I was unwell?"

Before you buy

Thrive Health Band: A$589 for the band including 12 months of the Thrive plan, paid upfront. Prices are in AUD and include GST.

Free shipping. Your 12 months start when you activate your Band, and there's no automatic renewal.

One size, IP68, up to 14 days battery, 12-month warranty, not a medical device, no Apple Health sync. The app is Thrive by Optihealth on iPhone and Android.

See today's price on the Thrive store

At renewal: a new band plus 12 more months for A$589.

Or keep your band and renew the plan for A$240 a year.

Or A$29 a month with no lock-in.

Consumer guarantees under Australian Consumer Law always apply. See Returns if something is wrong with your purchase.

Common questions

Is 37.5°C a fever?

Not by healthdirect's definition, which starts at 38°C. It's a little above the usual range, so rest, drink water and check again later. See your GP if you feel unwell or it keeps rising.

Is body temperature lower in the morning?

Usually, yes. Your body clock lowers core temperature overnight, and it rises again through the day.

Can a fitness band take my temperature?

The Thrive Health Band estimates your temperature from your wrist so you can see how it trends over time, and the app shows that trend against general ranges as a general guide. It isn't a diagnosis and doesn't replace a thermometer for checking a fever. Talk to your GP if you're worried.

For more answers, see Questions.