What is a normal temperature for a baby?

A normal rectal temperature for a baby is 97 to 100.3 degrees Fahrenheit (36.1 to 37.9 degrees Celsius). A rectal reading at or above 100.4 F (38 C) in an infant under 3 months is a medical emergency requiring immediate pediatric evaluation, per the American Academy of Pediatrics.

Which thermometer is most accurate for newborns?

A digital rectal thermometer is the gold standard for infants under 3 months, according to the AAP. The rectal method consistently gives the most accurate core temperature in this age group. Temporal artery (forehead) thermometers become reliable for infants 3 months and older when used correctly.

Can I use an ear thermometer on a newborn?

Tympanic (ear canal) thermometers are not recommended for infants under 6 months. A newborn's ear canal is too small and curved for accurate placement, which leads to unreliable readings. Wait until at least 6 months before using this method.

How do I take a rectal temperature safely without hurting my baby?

Use a flexible-tip digital rectal thermometer. Apply a thin layer of petroleum jelly to the tip. Lay your baby face-down on your lap or face-up with legs raised. Gently insert the tip no more than 0.5 to 1 inch (1 to 2.5 cm) into the rectum. Hold still until the thermometer beeps, usually within 10 to 20 seconds. Never force or push.

My toddler's axillary (armpit) reading was 99 F. Do I need to worry?

Axillary readings run 0.5 to 1 degree Fahrenheit lower than rectal readings. A 99 F armpit reading roughly corresponds to a rectal reading near 100 F, which is within normal range. If your child appears sick or the armpit reading exceeds 99.4 F, confirm with a rectal or temporal artery reading.

How to Take a Baby Temperature Accurately (2026 Guide)

Quick answer: The right thermometer depends on your baby’s age

For newborns through 3 months, a rectal digital thermometer is the most accurate method, and the one your pediatrician will trust. From 3 months to 4 years, a temporal artery (forehead) thermometer works well when swept correctly across the forehead. Ear thermometers are reliable from 6 months onward once the canal is wide enough for a proper seal. Oral readings are practical at 4 to 5 years, when a child can hold the probe still under the tongue for a full 20 to 30 seconds.

The single biggest mistake new parents make is reaching for whichever thermometer looks easiest without checking whether it suits their child’s age. An ear thermometer on a 6-week-old will almost always give a false-low reading. A forehead strip is decorative, not diagnostic.

Below are the techniques pediatric nurses use, broken down by age and method.

Rectal method: Most accurate for under-3-month infants

The American Academy of Pediatrics (AAP) states that rectal temperature is the most reliable measurement for infants under 3 months of age. The rectal route reads core body temperature directly, with a margin of error as low as plus or minus 0.2 degrees Fahrenheit in standard digital probes.

What you need:

A flexible-tip digital rectal thermometer (brands like Vicks, Frida Baby, or Safety 1st make dedicated rectal models)
Petroleum jelly (plain Vaseline)
A clean, flat surface or your lap

Step-by-step:

Clean the thermometer tip with rubbing alcohol or soap and water; rinse and dry.
Coat the tip with a thin layer of petroleum jelly, covering about 0.5 inches of the probe.
Lay your baby face-up on a changing table with their legs bent toward their chest, or face-down across your lap.
Gently spread the buttocks and locate the anal opening.
Slowly insert the tip no more than 0.5 to 1 inch (1.3 to 2.5 cm). Never force past resistance.
Hold the thermometer steady with two fingers against the buttocks while your other hand rests across the lower back to keep the baby from rolling. Most digital models beep within 10 to 20 seconds.
Remove the thermometer, wipe clean, and read the number. Record the value, the time, and the method used (“rectal”) before calling your doctor.

What is a fever? The AAP defines fever in infants as a rectal reading at or above 100.4 F (38 C). In infants under 3 months, any reading at or above this threshold is a medical emergency requiring same-day or emergency care, not a wait-and-see approach.

Safety note: Always label your rectal thermometer and store it separately. Thermometers used rectally should never be used orally, even after cleaning.

Temporal artery (forehead) method: Best from 3 months to 4 years

A temporal artery thermometer detects infrared heat from the skin over the temporal artery as you sweep it across the forehead. When used correctly, research published in peer-reviewed pediatric journals shows accuracy within about 0.3 degrees Fahrenheit of rectal readings in children over 3 months.

Popular models include the Braun ThermoScan 7, the Exergen Temporal Artery Thermometer (a standard in many US children’s hospitals), and the Frida Baby Quick-Read Digital Thermometer. These range from roughly $20 to $60 at current Amazon prices.

How to sweep correctly:

Remove hats, hair, or sweat from the forehead. Even a thin layer of moisture from crying or sweating will pull the reading down by 0.5 to 1 degree Fahrenheit.
Place the probe flat against the center of the forehead, just above the eyebrow.
Press and hold the scan button while slowly sweeping in a straight line to the hairline at the temple. The sweep should take about 2 to 3 seconds.
Some models require you to then lift the probe and touch it briefly behind the ear to capture a behind-ear reading. Follow the specific model’s instructions.
The thermometer beeps and locks the reading. Release the button.

Common errors that cause low readings: sweeping too fast, sweeping over hair, using it immediately after the baby comes in from cold air, or not pressing the probe firmly enough against the skin.

A rectal reading is still the confirmation method if a temporal reading seems inconsistent with how sick your child appears. If your 4-month-old is lethargic and pale but the forehead thermometer reads 99.8 F, take a rectal reading to confirm.

Ear (tympanic) method: Reliable from 6 months onward

Tympanic thermometers read infrared radiation from the eardrum, which reflects core body temperature closely because the eardrum shares blood supply with the hypothalamus, the brain’s temperature control center. The catch is that the ear canal must be straight enough to allow a proper seal, which it is not until around 6 months of age.

The Braun ThermoScan 7 IRT6520 is the most widely recommended model in clinical settings and is accurate to within plus or minus 0.4 degrees Fahrenheit in children over 6 months. It includes age-specific fever thresholds built into the display.

How to take an ear temperature:

Wait at least 15 minutes after being outside in cold or hot weather. Temperature extremes in the outer ear canal will skew results.
Gently pull the ear straight back (not upward as you would for an adult) to straighten the canal. This is the most commonly missed step.
Seat the probe snugly at the entrance to the ear canal. You should feel slight resistance when the seal is good. Do not push past resistance.
Press the button and hold for the full reading cycle, usually 1 to 2 seconds. A correct reading requires the probe to point at the eardrum, not the canal wall.
An active ear infection (otitis media) can cause a falsely elevated reading in the affected ear. Always use the unaffected ear when one ear is infected.

When ear readings mislead you: Wax buildup, a probe cover that is not fully seated, and too-rapid insertion are the three most common sources of error. Replace probe covers every single use.

Oral and axillary methods: For ages 4 and up

Oral reading is practical once a child can breathe through their nose and hold the thermometer still under the tongue for 20 to 30 seconds without biting. Most children reach this milestone reliably at 4 to 5 years. A digital oral thermometer like the Vicks Comfort Flex produces results in about 20 seconds and has a flexible stem that bends slightly for a more comfortable fit.

Place the probe tip under the tongue, as far back as possible on either side of the frenulum (the small ridge running down the center of the tongue). Instruct your child to close their lips gently, not their teeth. Wait for the beep.

Do not take an oral reading within 20 minutes of hot or cold food or drink. A cup of apple juice can suppress the reading by 1 to 2 degrees Fahrenheit.

Axillary (armpit) reading is the least invasive method and is sometimes used in toddlers when rectal is not practical. Place the thermometer tip in the center of the armpit, press the arm firmly against the body, and wait for the beep, usually 30 to 60 seconds on most digital models. Axillary readings run approximately 0.5 to 1 degree Fahrenheit below true rectal temperature. A 99 F axillary reading corresponds roughly to a 99.5 to 100 F rectal reading.

Use axillary readings as a screening tool only. If the axillary reading is above 99.4 F or your child appears genuinely unwell, confirm with a rectal or temporal artery reading before deciding whether to call your pediatrician.

What never to use: Forehead fever strips (the adhesive kind that change color) are not reliable enough for clinical use. They detect skin surface temperature, which can vary by 2 to 3 degrees depending on room conditions, sweating, and skin tone. They are fine for a quick sanity check but should not drive any medical decision.

Bottom line: Match the method to the age

Taking a baby’s temperature accurately is less about the specific thermometer brand and more about selecting the right method for your child’s age and using the technique correctly every time.

Birth to 3 months: rectal digital thermometer only
3 to 6 months: temporal artery (forehead) as primary, rectal to confirm
6 months to 4 years: temporal artery or tympanic ear thermometer
4 years and older: oral or temporal artery

Keep one dedicated rectal thermometer clearly labeled in your infant kit. A temporal artery thermometer like the Exergen Temporal Artery Thermometer is a sensible second thermometer that covers you from 3 months through the toddler years.

Check current Amazon pricing before you buy, as these fluctuate. Avoid relying on a single thermometer type for all ages and all situations. A rectal reading takes less than 20 seconds and is the single most reliable data point you can give your pediatrician when your baby is sick.

When to call your doctor immediately (per AAP guidelines):

Any fever (100.4 F rectal or higher) in a baby under 3 months
Fever above 104 F in a child of any age
Fever lasting more than 2 to 3 days in a child 2 years or older
Fever with stiff neck, severe headache, rash, difficulty breathing, or extreme lethargy

This article is for educational purposes and does not replace professional medical advice. Always contact your child’s healthcare provider with specific concerns about fever or illness.