The average body temperature, taken with a thermometer in the mouth, is 37ºC (98.6º F), but anywhere between 36.5º C and 37.2º C (97.7º F and 99º F) can be considered normal. Armpit temperatures are 0.2º C to 0.3º C lower than this. A fever in adults is a temperature of 38º C (100.4º F) or above.