The basal body temperature (BBT) varies from person to person and also depends on where you measure it. You can measure your basal body temperature orally, vaginally, or rectally. We do not currently recommend using skin temperatures as we need the core temperature to accurately measure the basal body thermometer.
Measurement of the temperature vaginally or rectally provides higher temperatures than measuring orally. It is important that you always measure in the same manner and the same place.