When your baby feels warm, you know it’s time to take their temperature. But getting an accurate reading depends entirely on the method you use.
Below, we’ll go over what type of thermometer is recommended for your baby based on their age and how to properly take their temperature with it.
The Best Baby Thermometer Method by Age
The most accurate method for checking your baby's temperature changes once they turn 6 months old.
Newborns to 6 Months Old
For the first 6 months, a **digital thermometer used rectally** is the best option. This method provides the most accurate temperature readings because it involves direct contact. If you use an all-in-one thermometer, be sure to label it, as the same thermometer should never be used for both rectal and oral temperatures.
Infants 6 Months Old or Older
Once your baby reaches 6 months old, you gain new (and often easier) options. You can use a digital thermometer under your baby’s armpit, a remote forehead monitor, or a remote in-ear thermometer.
Thermometers to Avoid
Thermometers not recommended for babies at any age include plastic strip thermometers, pacifier thermometers, and smartphone temperature apps because they do not provide accurate readings.
How to Take Your Baby’s Temperature Rectally
A rectal temperature is the gold standard for accurately knowing an infant’s temperature until they are over 6 months old. Here’s how to get an accurate reading.
Measuring Rectal Temperature with a Digital Thermometer
- Clean the digital thermometer by washing it with soap and water, or wiping it with rubbing alcohol.
- Lay your baby down either on their back or belly with their legs bent toward their chest.
- Apply petroleum jelly to the metal tip of the thermometer and gently glide it into the rectal opening—usually about half an inch, but always follow your specific thermometer’s instructions carefully.
- Turn on the thermometer.
- Hold the thermometer in place until it beeps, which typically takes about two minutes.
- Remove the thermometer and note the temperature.
- Clean the thermometer before storing it.
If you’re uncomfortable with this method, you can call a nurse line. They can walk you through the process over the phone.
How to Take Your Baby’s Temperature Under Their Arm
Taking your baby’s temperature under their arm (axillary method) is simple, but keep in mind that this reading is less accurate. It can be affected by the amount of clothing your baby is wearing, as well as the room temperature.
Measuring Armpit Temperature with a Digital Thermometer
- Remove your baby’s clothes so their chest is bare.
- Place the digital thermometer in one of their armpits.
- Fold their arm over the thermometer.
- Turn on the thermometer.
- Hold their arm in place until the thermometer beeps, which usually happens in less than two minutes.
- Remove the thermometer.
- Note the temperature, and remember to **add one degree to the reading** for a closer estimate.
Using a Remote Forehead Thermometer (Temporal Artery)
For babies older than 6 months, a temporal artery thermometer (TAT) is an easy way to measure your baby’s forehead temperature. A TAT uses infrared light to read the temperature of the temporal artery in the forehead.
The benefit is a quick reading, meaning your little one won’t need to hold still for long. However, these readings can be less accurate than digital thermometers.
How to Use a Temporal Artery Thermometer
- Make sure your baby’s forehead is clean and dry.
- Hold the thermometer in front of the baby’s forehead at the correct distance (check your model’s directions).
- Hold down the button and wait for the thermometer to beep—this should only take a few seconds.
- Note the temperature.
Using a Remote In-Ear Thermometer (Tympanic)
Another option for babies 6 months and older is an in-ear (tympanic) thermometer. This device measures the temperature of the eardrum using infrared light.
A tympanic thermometer has a small cone-shaped probe for the ear canal. If used correctly, in-ear thermometers can provide reliable readings. However, they may be less accurate if your baby has earwax buildup or a small, curved ear canal.
How to Use a Tympanic Thermometer
- Check the inside of your baby’s ear to make sure it’s clean.
- Clean the tip of the probe with rubbing alcohol.
- Gently tug your baby’s ear straight back to make room for the probe.
- Gently ease the probe into the ear canal.
- Press the button and hold the thermometer in place until it flashes or beeps (usually just a second or two).
- Remove the thermometer and note the temperature.
Next Steps After Taking the Temperature
If your baby does have a temperature, the good news is that most fevers can be monitored and treated at home. What you should do next depends on your child’s age and how high their fever is. You should always consult with your pediatrician or a healthcare professional for specific advice on treating a fever and knowing when it's time to see a doctor.
Frequently Asked Questions: Baby Temperature
A. A rectal temperature of 100.4°F (38°C) or higher is generally considered a fever in babies. For armpit readings, a temperature of 99°F (37.2°C) or higher usually indicates a fever, as this method is less accurate than the rectal method.
A. If your baby has a fever and is generally comfortable, you can check their temperature every 4 to 6 hours. If they are sleeping peacefully, do not wake them up just to check the temperature. If the fever is very high or your baby is acting unusually sick, check it more frequently.
A. You should call a doctor immediately if your baby is under 3 months old and has a rectal temperature of 100.4°F (38°C) or higher, or if your baby seems lethargic, has difficulty breathing, or the fever lasts more than 24 hours.