“what temperature is a fever?”
Last updated September 6, 2026.
**A fever is a body temperature of 100.4°F (38°C) or higher.** Normal is a range, not one number: most healthy adults sit between about 97°F and 99°F, and your reading is lowest in the morning and highest in the late afternoon. Where you measure changes the result, so rectal and ear readings tend to run higher than oral, while armpit and forehead readings tend to run lower. Readings between 99°F and 100.3°F are usually called a low-grade or elevated temperature rather than a fever. In adults, how sick you feel and what other symptoms you have matter more than the exact number on the thermometer. Take your temperature before eating, drinking, or exercising, and write down the number, the time, and the method you used so you can track the pattern.
What to do
- Use one method: Take every reading the same way and at similar times so the numbers can be compared.
- Check babies rectally: For infants under 3 months, a rectal reading of 100.4°F or higher means call a clinician right away.
- Watch the whole picture: Track breathing, alertness, fluid intake, and pain along with the number, not the number alone.
- Treat the discomfort: Acetaminophen or ibuprofen at label doses can ease aches, and steady fluids and rest help you feel better.
- Know the 3-day mark: A fever that lasts more than 3 days, tops 103°F, or returns after clearing should be reviewed by a clinician.
- Act fast on red flags: Confusion, trouble breathing, stiff neck, a new rash, seizure, or a fever with a weakened immune system needs emergency care.
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