Is it a fever?
Fever starts at 100.4°F, or 38°C. Enter the reading and where you measured; the checker corrects for method and tells you plainly what to do.
Armpit readings run about half a degree low; the checker corrects for where you measured.
Keep checking through an illness? Log it in the symptom diary.
Common questions
What temperature is considered a fever?
100.4 F (38 C) and above is a fever, measured orally. Readings from 99.5 to 100.3 F are low-grade and often just the body warming through the day, after exercise, or early in an infection. Normal is a range: most healthy adults run 97 to 99 F, lowest in the morning.
Is 99.5 a fever?
Not officially. It is low-grade territory, worth rechecking after a few quiet minutes, since a hot drink, a warm room, exercise or simply the afternoon can put a healthy person there. If it keeps climbing past 100.4 F, it is a fever.
When is a fever dangerous?
For adults: 104 F (40 C) and above, a fever lasting beyond 3 days, or any fever with a stiff neck, confusion, a rash that does not fade under a glass, trouble breathing, or severe headache; those need same-day care. For a baby under 3 months, 100.4 F is itself the emergency line. Anyone on chemotherapy with a fever needs urgent care regardless of the number.
Should I treat a fever or let it run?
Fever is the immune system working, and treating it is for comfort, not cure. If you feel miserable, acetaminophen or ibuprofen at package doses helps. If you feel tolerable, resting and drinking steadily is a fine choice. What matters is the pattern and the red flags, not forcing the number down.
Do forehead and armpit thermometers read differently?
Yes. Armpit readings run about half a degree F lower than oral; rectal readings run about half a degree higher and are the standard for babies. Forehead scanners are convenient but drift with sweat and technique. Whichever you use, use the same one through an illness so the trend is honest.