Basal Body Temperature

Your basal body temperature is your body temperature at complete rest, traditionally taken immediately on waking, before getting out of bed. It sits around 36.1 to 36.4 degrees Celsius for most people in the first half of a menstrual cycle.

What makes it worth recording is a shift rather than a level. After ovulation, progesterone raises it by roughly 0.3 degrees Celsius, and that higher level holds until the next period begins. A chart of a whole cycle shows two distinct plateaus with a step between them.

The step confirms that ovulation happened, which no calendar estimate can do. It confirms it after the fact rather than predicting it, so on its own it is a record rather than a forecast, and several cycles of records make the forecast better.

What it is not

The rise is small, and almost anything will hide it: a poor night's sleep, alcohol, illness, a different thermometer, or taking the reading at a different time. A wearable that measures skin temperature overnight is measuring something related but not the same, and it reports a deviation from your own normal rather than an absolute.

Where you see it in FitnessSyncer

Temperature readings arrive from any connected device that records them and can be logged in the Notebook, charted on your Dashboard and shown alongside your cycle tracking data.