Bottom line up front: the best baby thermometer is a digital rectal thermometer for the first months, plus a forehead (temporal artery) thermometer once you want quicker, less invasive checks. The American Academy of Pediatrics ranks rectal readings as the most accurate and forehead readings as next most accurate, and says a rectal temperature “gives the best reading, especially for infants under 3 months of age.” So a short, flexible-tipped rectal stick like the Frida Quick-Read Digital Rectal Thermometer is the one non-negotiable buy. A temporal-artery scanner such as the Exergen TAT-2000C is the best second thermometer, and an ear thermometer only earns a place after six months.
This page is organised by age and method rather than by brand. That is how the guidance is written, and it is the question you are actually asking at 2 a.m. My minimalist registry checklist already puts “baby thermometer, rectal, unglamorous, accurate” on the short list. This is the longer answer to which one. All accuracy and age guidance below is quoted from the AAP’s parent site, HealthyChildren.org, loaded on 11 October 2026.
The accuracy ranking that decides the purchase
HealthyChildren’s guide to taking a child’s temperature is unusually direct about the order:
“Rectal (in the anus) temperatures are the most accurate. Forehead temperatures are the next most accurate. Oral and ear temperatures are accurate if done properly. Armpit temperatures are the least accurate, but you can use this method to screen a child of any age.”
It also sets age limits on two of the methods. Oral use “is not recommended until a child is age 4 or older,” and ear thermometers “can be used on children age 6 months and older” because they are “not reliable for younger babies, whose ear canals are too narrow.” It is also clear about the device type: “It is best to use a digital thermometer to check your child’s temperature. Do NOT use a mercury thermometer.”
Put together, that gives a buying table:
| Method | Usable from | AAP accuracy note | Pick |
|---|---|---|---|
| Rectal (digital stick) | Birth | Most accurate; best under 3 months | Frida Quick-Read Rectal |
| Forehead (temporal artery) | Any age | Next most accurate | Exergen TAT-2000C |
| Ear (tympanic) | 6 months | Accurate if placed properly | Braun ThermoScan 7 |
| Oral (digital stick) | 4 years | Accurate if done properly | Vicks SpeedRead |
| Armpit (digital stick) | Any age | Least accurate; screening only | Same stick as oral |
| Non-contact forehead | Any age | Follow distance instructions | Braun No Touch 3-in-1 |
Under 3 months: a rectal thermometer, full stop
This is the one age band where the choice is made for you. HealthyChildren’s fever and your baby page says a rectal reading “is the most reliable and accurate for infants, especially babies under 3 months old,” and the number that triggers a call to the pediatrician at this age is a rectal one. If you only own a forehead or ear thermometer when your newborn feels hot, you will be asked for a rectal reading anyway.
The pick: Frida Quick-Read Digital Rectal Thermometer. It is the design most parents are nervous about rather than the brand. Frida’s own product page describes a “safe flexible tip and stopper” meant to keep it from being inserted too far. It also lists a 10-second read, a “large, backlit display for nighttime temp checks” and memory for the last 10 readings. It was $16.99 on frida.com when I checked on 11 October 2026. The stopper is the useful part: HealthyChildren’s instructions are to insert “1/2 inch (for babies less than 6 months old) to 1 inch,” and a physical stop takes the guesswork out of that.
The cheaper alternative: the Vicks Baby Rectal Thermometer, which also uses a short, flexible tip. Either does the job. What matters is that it is digital, short and kept for rectal use only.
HealthyChildren’s technique, in brief: a little petroleum jelly on the tip, baby belly down across your lap or on their back with legs pulled up, gentle insertion with no resistance (“If there is, stop”), hold still until it beeps. Clean it before and after, and label it. The AAP says to “label the rectal thermometer so it is not accidentally used in the mouth.” A strip of tape with an R on it is fine.
Any age: a temporal artery (forehead) thermometer
Once your baby is past the newborn weeks, the thermometer you will reach for most is the one that does not wake a sleeping child. HealthyChildren says temporal artery thermometers “can be used on children of any age,” and ranks forehead readings second only to rectal for accuracy.
The pick: Exergen TAT-2000C. It is a contact, swipe-across-the-forehead design, and its listing names newborns, kids and adults as users. It is not a replacement for the rectal stick under three months. It is the thermometer that answers “is this worth a rectal reading?” without a fight.
Two conditions from the AAP page are worth knowing before you trust a forehead number: “Direct sunlight and cold temperatures after being outside may affect reading.” If you have just come in from a cold stroller walk, wait before reading. And follow the package instructions on where and how to swipe, because the method is the accuracy.
The non-contact version: the Braun No Touch 3-in-1 reads without touching the skin. HealthyChildren notes non-contact models “may help reduce the risk of passing germs,” and tells you to “check the instructions to find out how close to the forehead” to hold it. It is the better choice if you have several sick children and one thermometer. If accuracy is the priority, a contact temporal-artery swipe is the more conservative buy.
From 6 months: an ear thermometer, if you will learn to place it
Ear thermometers are fast, and older babies tolerate them well. They are also the method most dependent on technique. HealthyChildren is specific: “A correct temperature depends on pulling the ear back. Pull the ear back and up if the child is over 1 year old. Then aim the tip of the ear probe between the opposite eye and ear.” It adds that a cold day can cause a low reading, so “wait 15 minutes after coming indoors.”
The pick: Braun ThermoScan 7. It takes disposable lens filters, so budget for refills. Skip it if your baby is under six months, or if you already own a temporal-artery thermometer and do not want two forehead-speed devices. For most families, rectal plus forehead covers every age, and the ear thermometer is a preference rather than a need.
The stick for older kids: oral and armpit
A basic digital stick does three jobs: rectal, oral from age four, and armpit screening at any age. The catch is the labelling rule. One stick should never move between rectal and oral use, so in practice you buy two and mark them.
The pick: Vicks SpeedRead Digital Thermometer. It is an inexpensive, widely available stick. Buy it as your oral and armpit thermometer once your child is old enough, and keep the rectal one separate. For oral readings, HealthyChildren says to wait 30 minutes after a hot or cold drink, place the tip “under one side of your child’s tongue toward the back of the mouth,” and keep the lips sealed until it beeps.
What to skip
- Mercury thermometers. The AAP says not to use them: the thin glass “can break and release toxic levels of mercury fumes.” If an old one is in a drawer, it should go.
- Fever strips. HealthyChildren lists “fever strips on the forehead” among the less accurate options, fine for “quick screening” but not as good as a digital reading. Its fever-and-your-baby page puts it more bluntly: “temperature sensitive tape or ‘fever strips’ also is not reliable.”
- Pacifier thermometers. Named by the AAP alongside fever strips as a less accurate screening method.
- Your hand on their forehead. “Quick but not very exact,” per the AAP. It tells you to go and find the thermometer, not what the temperature is.
The numbers that mean “call now”
A thermometer is only useful if you know what to do with the number. From HealthyChildren’s when to call the pediatrician page, call your child’s doctor right away if your child has a fever and:
- is younger than 3 months (12 weeks) with a temperature of 100.4°F (38.0°C) or higher;
- has a temperature that rises above 104°F (40°C) repeatedly, at any age;
- looks very ill, is unusually drowsy, or is very fussy;
- still “acts sick” once the fever is brought down;
- has had a fever for more than 24 hours and is younger than 2, or more than 3 days and is 2 or older.
The fever-and-your-baby page adds that you “may need to notify the doctor” if a baby between 3 and 6 months has a fever of 101°F (38.3°C) or higher, or a baby older than 6 months reaches 103°F (39.4°C) or higher. This post gives no advice on treating a fever. Medication and dosing are a conversation with your pediatrician, by weight.
If the fever comes with a blocked nose and a miserable night, the nasal side of the same cold is covered in my nasal aspirator comparison. Betteroo’s guide to how sleep changes while a baby is unwell covers the overnight side: more wakings, keeping the crib flat, and when to wake a sick baby to feed.
The setup I would buy
- Before birth: one short, flexible-tipped digital rectal thermometer, labelled R.
- Around the first cold: a temporal-artery forehead thermometer for screening.
- Optional, from 6 months: an ear thermometer, if you prefer it and will practise the placement.
- From age 4: a separate digital stick for oral readings, labelled O.
Keep the rectal one and a small tub of petroleum jelly in the same drawer. When you are travelling, a thermometer belongs in the small medical pouch in my diaper bag checklist.
FAQ
What is the best thermometer for a newborn?
A digital rectal thermometer. The AAP says rectal readings are the most accurate and give the best reading “especially for infants under 3 months of age,” and the fever threshold for calling the doctor at that age (100.4°F) is a rectal reading. A short, flexible tip with a stopper makes it easier to use correctly.
Are forehead thermometers accurate for babies?
Temporal artery (forehead) thermometers are the second most accurate method in the AAP’s ranking and can be used at any age. Cold air, direct sunlight and poor technique can throw the reading off. Under 3 months, confirm a high forehead reading with a rectal one.
Can I use an ear thermometer on a baby under 6 months?
No. HealthyChildren says ear thermometers are “not reliable for younger babies, whose ear canals are too narrow,” and should be used from 6 months.
What temperature counts as a fever in a baby?
The AAP defines a fever as usually 100.4°F (38°C) or higher. For a baby under 3 months, a rectal reading at or above that is a reason to call your pediatrician immediately, even if the baby seems otherwise well.
Do I need more than one thermometer?
Most families end up with two: a rectal stick for the early months and a forehead thermometer for everyday checks. If you add an oral stick later, label it, because one thermometer should never be used in both places.
