Learn How To Check Your Baby's Temperature

Understanding Normal Baby Temperature Ranges

Knowing what counts as a normal temperature for your baby is the first step in monitoring their health. Babies' body temperatures work differently than adults', and the range considered normal can vary depending on your baby's age and the method used to measure temperature.

For infants under three months old, a rectal temperature of 100.4°F (38°C) or higher is considered a fever. This age group requires special attention because fever in very young babies can indicate a serious infection. Rectal temperature is considered the gold standard for accuracy in this age group because babies cannot hold a thermometer in their mouth safely.

For babies between three months and three years old, a rectal temperature above 102°F (39°C) is typically considered a fever. However, some healthcare providers use 101°F (38.3°C) as the threshold. During this age range, your baby's immune system is still developing, so temperatures may fluctuate more than in older children.

Normal temperature ranges also vary by the time of day. Body temperature naturally rises in the afternoon and early evening and drops in the early morning. Your baby's temperature may be about 1°F lower in the morning and up to 1°F higher in the evening. This is perfectly normal and not a cause for concern.

The method you use to take your baby's temperature matters. Rectal readings tend to be about 0.5°F higher than oral readings and about 1°F higher than armpit readings. If you switch between different methods, remember these differences when comparing readings.

Practical takeaway: Keep a record of your baby's normal temperature range at different times of day. This personal baseline helps you recognize when something may be off and provides valuable information to share with your pediatrician during a visit.

Choosing the Right Thermometer for Your Baby

Several types of thermometers are available for measuring baby temperatures, and each has advantages and disadvantages. Understanding your options helps you select the tool that works best for your family's needs.

Digital thermometers are the most commonly recommended choice for babies. They provide fast, accurate readings—typically within 30 seconds to 2 minutes depending on the model. Digital thermometers can be used rectally for infants under three months, which provides the most accurate reading for this age group. Look for thermometers with a flexible tip, which is more comfortable for babies. Digital thermometers are affordable, durable, and easy to read, making them a practical choice for most families.

Temporal artery thermometers (forehead thermometers) scan the temporal artery on the forehead and provide a reading in about 1 second. These are non-invasive and quick, making them popular with parents. However, studies show they can be less accurate than rectal readings, especially in very young infants. They work better for babies over six months old. Sweat, hair, or recent sun exposure on the forehead can affect accuracy.

Ear thermometers (tympanic thermometers) measure the heat radiating from the eardrum. They're quick and non-invasive but can be inaccurate in babies under three months because their ear canals are too small and curved. They also require careful positioning to get an accurate reading, which can be difficult with a squirming baby.

Avoid mercury thermometers entirely. If you have an old mercury thermometer at home, dispose of it properly through a hazardous waste facility. Mercury is toxic and poses serious health risks if the thermometer breaks. Pacifier thermometers and thermometer strips that change color are not reliable enough for medical decisions about your baby.

Practical takeaway: Invest in a quality digital thermometer with a flexible tip as your primary tool. Keep it stored in a safe, accessible place and check that the batteries work before you need it in an emergency.

How to Take Your Baby's Temperature Rectally

Taking a rectal temperature is the gold standard for babies under three months old because it provides the most accurate reading. While this method may feel uncomfortable at first, it becomes routine with practice. Your pediatrician can demonstrate the technique during a visit if you're unsure.

Before you start, gather everything you need: a digital thermometer, lubricant like petroleum jelly or a water-soluble lubricant, a tissue or wipe, and something to clean the thermometer afterward. Having everything ready prevents you from leaving your baby unattended while searching for supplies.

Place your baby on their back on a soft surface like a changing table or bed. You can also hold your baby on your lap with their back against your chest. Clean the thermometer tip with soap and warm water or an alcohol wipe, then apply a small amount of lubricant to the tip. This reduces friction and discomfort.

Gently insert the thermometer into your baby's rectum, pushing it in about 0.5 inches (1.3 centimeters). Hold it steady and wait for the beep. Most digital thermometers beep when the reading is complete, typically within 1-2 minutes. Keep your hand on the thermometer the entire time to prevent it from going in too far or being pushed out suddenly.

Remove the thermometer slowly and gently. Note the reading immediately, as it's easy to forget after dealing with a fussy baby. Clean the thermometer with soap and warm water and dry it completely before storing.

Practical takeaway: Practice this technique when your baby is calm and content, not when they have a fever and may be uncomfortable. Staying calm yourself helps keep your baby calm during the process.

Taking Armpit and Forehead Temperatures in Older Babies

As your baby grows older, taking temperatures under the arm (axillary method) becomes more practical. This method works well for babies over three months old, though it's slightly less accurate than rectal temperature. It's non-invasive and easier to manage with an active toddler.

To take an armpit temperature, remove your baby's shirt or pull it up to expose the armpit area. Make sure the skin is dry. Place the thermometer tip directly in the center of the armpit and hold your baby's arm down against their body to keep the thermometer in place. Keep it there for the full time recommended by your thermometer—usually 1-3 minutes for a digital thermometer. Wait for the beep, then remove and read the temperature.

Remember that armpit temperatures run about 1°F lower than rectal temperatures. If your baby's armpit temperature is 99.4°F (37.4°C), this is roughly equivalent to a rectal temperature of 100.4°F (38°C). This is an important detail when communicating with your pediatrician about whether your baby has a fever.

Forehead thermometers work well for babies over six months old who can sit still for a moment. These temporal artery thermometers scan across the forehead and provide a reading in seconds. Ensure the forehead is clean and dry, and follow the manufacturer's instructions for proper positioning and speed of the scan. Some models require you to swipe the thermometer across the forehead, while others need you to hold it at a specific angle.

Neither armpit nor forehead readings are as reliable as rectal temperatures for very young babies. If you're concerned about fever in a baby under three months old, use a rectal thermometer to get the most accurate information before contacting your pediatrician.

Practical takeaway: As your baby gets older, test different thermometer methods to see which one works best with your baby's temperament. Some babies tolerate forehead scans better than armpit readings, and knowing your baby's preference helps you get accurate readings when needed.

Reading and Recording Temperature Results

Once you have a temperature reading, it's important to understand what the number means and keep track of the reading for future reference. This information helps your pediatrician understand patterns and make informed decisions about your baby's care.

Write down the temperature reading, the time you took it, which method you used, and any symptoms your baby is showing. For example: "3:45 PM, rectal temp 101.2°F, fussy and not eating as much as usual." This level of detail provides context that matters when talking with your healthcare provider. A single elevated temperature might be normal variation, but a pattern of rising temperatures or temperatures