A temperature of 98°F is not a fever. It falls squarely within the normal range for a healthy human body. The widely accepted medical threshold for a fever is 100°F or higher when measured orally, meaning 98°F sits a full two degrees below that cutoff.
Why 98.6°F Isn’t the Magic Number
You’ve probably heard that 98.6°F is “normal” body temperature. That number dates back to the 1800s, and while it’s a reasonable ballpark, modern research paints a slightly different picture. A systematic review of 36 studies found the actual average human body temperature is closer to 97.9°F, with a normal range spanning roughly 97.1°F to 98.6°F. So a reading of 98°F is almost exactly average.
Your body temperature also isn’t a fixed number. It shifts throughout the day, running lower in the morning and peaking in the late afternoon or evening. Exercise raises it. Menstrual cycles shift it. A reading of 98°F at 7 a.m. reflects a slightly warmer baseline than the same reading at 5 p.m., when your body naturally runs hotter. These daily swings of about one degree are completely normal and don’t indicate illness.
Where You Measure Matters
Not all thermometer readings are interchangeable. Rectal temperatures run about 0.7°F to 0.8°F higher than armpit (axillary) readings. Oral measurements fall somewhere in between. If you took a 98°F reading under your arm, your core temperature is likely a bit higher. If it was a rectal reading, 98°F is on the lower end of normal but still perfectly fine.
For accuracy, oral thermometers are the most common choice for adults. Place the tip under your tongue, keep your mouth closed, and wait for the beep. Avoid taking your temperature right after drinking something hot or cold, since that can throw off the reading by a degree or more.
What Actually Counts as a Fever
The Mayo Clinic defines a fever as an oral temperature of 100°F or higher. That’s the number most doctors use as a starting point. A temperature between 99°F and 100°F is sometimes called a “low-grade” temperature, though it doesn’t meet the clinical definition of fever for most adults. It could simply reflect normal daily variation, recent physical activity, or warm clothing.
For children, the thresholds depend on age. The American Academy of Pediatrics defines fever as any temperature above 100.4°F regardless of age. But risk levels vary: a baby under 3 months old with a temperature of 100.4°F or higher is considered high-risk for serious illness and needs prompt medical evaluation. For toddlers between 3 and 36 months, a reading above 99.6°F is flagged as a fever, while older children have a slightly higher threshold of 99.9°F before concern kicks in.
Fever Thresholds Shift With Age
Older adults tend to run cooler than younger people. The daily range of temperature narrows with age, and baseline readings often sit lower. Because of this, a temperature that looks “normal” on paper might actually represent a significant jump for someone over 65. Clinical guidelines recommend that an increase of at least 2°F above a person’s individual baseline should be treated as a fever in elderly patients, even if the thermometer doesn’t hit 100°F. For someone whose usual temperature is 97°F, a reading of 99°F could signal an infection.
When 98°F Feels Wrong
Sometimes you feel feverish even when the thermometer says otherwise. Chills, body aches, and fatigue can all show up before your temperature officially crosses into fever territory. Your immune system activates in stages, and the subjective “I feel sick” sensation can arrive before measurable heat builds up. If your baseline tends to run low, say around 97°F, then 98°F represents a full degree increase and your body may notice the shift even though the number looks unremarkable.
Dehydration, anxiety, hormonal changes, and certain medications can also make you feel warm without raising your core temperature into fever range. If you feel unwell but your temperature is 98°F, it’s worth checking again in a few hours. Fevers often develop over time, particularly in the evening when your body’s natural thermostat is already set a bit higher.
What a Low Temperature Means
While 98°F is normal, readings that dip well below that range can be concerning in the opposite direction. Hypothermia begins at 95°F, when the body loses heat faster than it can produce it. Persistent readings in the low 96°F range without an obvious cause (like being in a cold environment) are worth mentioning to your doctor, as they can occasionally point to thyroid issues or other metabolic conditions. But a reading anywhere from 97°F to 99°F on a standard oral thermometer is nothing to worry about.