How to Take a Baby's Temperature

Your baby feels warm. Maybe warmer than usual, maybe you are not sure, and now you are standing in the hallway at 11pm holding a thermometer you have never actually used. Learning how to take a baby's temperature is one of those skills nobody teaches you before you leave the hospital, and it always seems to come up for the first time when you are tired and a little worried.

The good news is that it is genuinely simple once you have done it once. There are only a handful of methods, each one takes under a minute, and the technique matters more than the gadget. Where parents usually get tripped up is not the measuring itself, it is knowing which method to use at which age, and what the number actually means afterward.

This guide walks through each method step by step, shows typical ranges side by side, and covers when it makes sense to call your pediatrician. Every baby is different, so treat this as a friendly starting point rather than a rulebook.

Pippy says:

Practice once on a calm afternoon when nobody is sick. It is a lot easier to learn the motion when you are not also worried.

Which Method to Use at Each Age

The method that makes sense depends almost entirely on how old your baby is. For newborns and babies under 3 months, most pediatricians ask for a rectal temperature, because that is the reading they trust when deciding whether a young baby needs to be seen. At that age a fever is taken seriously regardless of how happy the baby seems, so accuracy really matters.

Between roughly 3 months and 6 months, a rectal reading is still the gold standard, though many families start using an armpit or forehead thermometer for a quick first check and only confirm rectally if the number looks high. From about 6 months onward, forehead and ear thermometers become more practical, especially with a squirmy baby who has strong opinions about being held still.

One thing worth knowing early: you should have a dedicated rectal thermometer that never gets used anywhere else, clearly labeled so nobody mixes them up. Digital stick thermometers are inexpensive, so keeping one for rectal use and one for oral or armpit use is an easy call. Mercury glass thermometers are no longer recommended for any age because of the breakage risk.

How to Take a Rectal Temperature

This is the part most parents dread, and it is almost always easier than expected. Your baby may fuss, but it does not hurt them when done gently, and the whole thing is over in under a minute. Start by washing the thermometer tip with soap and cool water or wiping it with rubbing alcohol, then rinsing. Put a small dab of petroleum jelly on the tip.

Lay your baby down in whichever position feels steadier to you. Some parents prefer belly down across their lap with one hand resting on the lower back, others prefer the baby on their back with knees gently bent toward the chest, the same position you already know from diaper changes. Turn the thermometer on, then slide the tip gently into the rectum about half an inch to one inch. Never force it. If you feel resistance, stop and reposition.

Hold the thermometer steady with your fingers resting against your baby's bottom so it cannot slide in further if they wiggle. Keep your other hand on their legs or back. Wait for the beep, usually somewhere between ten and thirty seconds depending on the model, then remove it and read the number. Clean the thermometer again before putting it away. Many parents find that talking or singing through the whole thing keeps everyone calmer, including themselves.

Armpit, Forehead, and Ear Readings

An armpit (axillary) reading is the gentlest option and works at any age. Tuck the thermometer tip into a dry armpit, making sure it is touching skin on all sides rather than sitting in a fold of clothing, then hold your baby's arm snugly down against their side until it beeps. Armpit readings run lower than rectal ones, and the difference varies from baby to baby, which is why it is best used as a screening check rather than the final word.

Temporal artery thermometers, the kind you sweep or hold across the forehead, are fast and easy to use on a sleeping baby. They can be quite good when used exactly as the instructions say, which usually means starting at the center of the forehead and sweeping toward the hairline, not down the face. Sweat, a hot room, or a baby who was just unwrapped from a blanket can all skew the result, so a quick second reading is worth doing if the first one surprises you.

Ear (tympanic) thermometers are generally not recommended for babies under 6 months, because a young baby's ear canal is small and curved enough that positioning errors are common. For older babies they work well, as long as you gently pull the ear back and up to straighten the canal first. Earwax or a recent bath can affect the reading. Whichever method you use, note down which one it was, because your pediatrician will want to know.

Normal Temperature Ranges by Method

These ranges give you a rough sense of what typical looks like, but a single number never tells the whole story on its own. A baby's temperature naturally runs a bit lower in the early morning and higher in the late afternoon, and crying, a warm room, or a heavy sleep sack can nudge it up temporarily. What your pediatrician cares about is the number, the method, and how your baby is behaving.

Notice that the armpit threshold sits lower than the others. That is why converting between methods by adding a degree is not reliable. Report what you actually measured and say which method you used, and your pediatrician will interpret it from there. If you want a deeper look at what different fever readings mean, our guide on baby fever and when to call the doctor goes through it in more detail.

Things That Throw Off a Reading

Before you panic at a number, it helps to rule out the ordinary explanations. A baby who has been bundled in a fleece sleep sack in a warm room can read a little higher than they truly are. So can a baby who has just finished a long crying session, or one who was napping face down against your chest. Unwrapping your baby for five to ten minutes and taking the reading again often tells a clearer story.

On the other end, a cold thermometer tip, a damp armpit, or a forehead scan done right after coming in from outside can read artificially low. Batteries matter too. A thermometer that is giving wildly different numbers three times in a row usually needs new batteries rather than a new interpretation. If your readings are inconsistent, take two or three and look at whether they cluster.

The most useful piece of information is not on the thermometer at all. How is your baby acting? A baby with a mild fever who is feeding, alert between naps, and producing wet diapers is a different picture than a baby with the same number who is limp, refusing feeds, or unusually difficult to wake. Keeping an eye on signs of dehydration and diaper output alongside the temperature gives your pediatrician a much fuller picture.

Pippy says:

Write down the time, the number, and the method every single time. Three readings on a timeline say far more than one number remembered from an hour ago.

Keeping Track of Readings

When a baby is under the weather, the questions your pediatrician asks are almost always about pattern rather than peak. When did it start? What has it been doing over the last twelve hours? Did anything bring it down, and for how long? Those are hard questions to answer accurately from memory, especially on very little sleep.

Many parents find it helps to log each reading right after taking it, along with the method and anything else happening at the time, like a dose of medication cleared with your pediatrician, a refused bottle, or a dry diaper stretch. A short note takes ten seconds and saves you from reconstructing the day at the front desk of the clinic.

If both parents are involved in care, shared notes are even more useful, since the person on the phone with the doctor is not always the person who took the last reading. Our post on splitting baby duties with a partner covers a few ways to keep everyone in sync without constant check in texts.

When to Call Your Pediatrician

Pediatric offices genuinely would rather hear from you than have you wait and worry, and there is no such thing as calling too early about a young baby. The general guidance is that any rectal temperature of 100.4 degrees Fahrenheit or higher in a baby under 3 months old warrants a call right away, day or night, even if your baby otherwise seems fine. Babies that young have less to show on the outside, so the number carries more weight.

For older babies, most pediatricians want to hear about a fever that lasts more than a day or two, a fever above roughly 102 degrees Fahrenheit, or any fever paired with things like unusual sleepiness, refusing to feed, far fewer wet diapers than normal, a rash, or labored breathing. A temperature that is unusually low can matter too, so mention that as well.

Trust your read on your own baby. If something feels off even without a dramatic number, that is a good enough reason to call. You know your baby's normal better than any chart does, and every pediatrician's office has taken that call a thousand times before.

Pippy says:

Never give fever medication to a baby without checking with your pediatrician first, especially under 6 months. Dosing depends on weight, not age.