Normal Body Temperature: Ranges by Age, Method & When It’s a Fever
What is a normal body temperature?
The textbook figure of 98.6°F (37°C) is a 19th-century average. Modern studies put the typical adult range at roughly 97°F to 99°F (36.1–37.2°C), with readings naturally lowest in the early morning and highest in the late afternoon. Body temperature also declines slightly with age and varies by about half a degree across the menstrual cycle.
Get an accurate reading
- Wait 15 minutes after eating, drinking, or exercise before an oral reading.
- Measure at the same time of day when tracking a trend - afternoon readings run about 1°F higher than early morning.
- Stick to one method. Ear, forehead and oral readings differ by up to a degree, so comparisons only work within one method.
Normal ranges by age
| Age group | Normal range (°F) | Normal range (°C) |
|---|---|---|
| Babies (0–2 years) | 97.9–100.4°F | 36.6–38.0°C |
| Children (3–10) | 97.0–100.0°F | 36.1–37.8°C |
| Adults (11–65) | 97.0–99.0°F | 36.1–37.2°C |
| Older adults (65+) | 96.4–98.5°F | 35.8–36.9°C |
Measurement method matters
| Method | Compared with oral | Notes |
|---|---|---|
| Oral | Baseline | Wait 15 min after hot/cold drinks |
| Rectal | +0.5 to +1°F higher | Most accurate for infants |
| Ear (tympanic) | +0.5 to +1°F higher | Position affects accuracy |
| Forehead (temporal) | ≈0 to -0.5°F lower | Fast, slightly less precise |
| Armpit (axillary) | -0.5 to -1°F lower | Least accurate common method |
When is it a fever?
The widely used medical threshold for fever is 100.4°F (38°C). Between about 99.1°F and 100.3°F is often described as a low-grade elevation. See our fever temperature chart for severity levels and when to seek care. A single slightly-high reading in a comfortable, well-appearing person usually just reflects the daily rhythm, exercise, or a warm room - recheck after 30 quiet minutes.
Why the textbook 98.6°F is outdated
The famous 98.6°F comes from a German study of the 1860s. Modern datasets tell a cooler story: average adult body temperature has drifted down over the past 150 years, and large recent studies put today's typical oral average near 97.9°F (36.6°C). Better thermometers, lower rates of chronic infection and changed metabolism all likely contribute.
The practical takeaway: judge readings against a range (97-99°F for most adults) and against your own baseline, not against a single 19th-century number.
What moves your temperature day to day
- Time of day: lowest around 4-6 AM, highest in late afternoon - a swing of about 1°F.
- Exercise: hard workouts can raise core temperature 2-3°F for a while afterward.
- The menstrual cycle: a sustained rise of roughly 0.5-1°F follows ovulation (the basis of basal body temperature charting).
- Age: older adults run cooler and may mount smaller fevers, so a “mild” reading can understate illness.
- Hot drinks, meals and weather: transient effects worth waiting out before you measure.