BBT Calculator

Why Adjust Basal Body Temperature?

Basal body temperature (BBT) charting relies on taking your temperature at the same time each morning before getting up. If you wake later or earlier than usual, your reading may not be comparable. This calculator normalizes the measurement to your usual wake-up time.

BBT Adjustment Formula

First find the time difference in minutes: usual time minus actual time. Then compute the temperature correction as $(\text{time difference} / 30) \times 0.05$ °C, because body temperature rises about 0.05 °C per 30 minutes after waking. If the correction is negative, subtract its magnitude from the measured temperature; otherwise add it.

Example

Usual time 07:00, actual time 07:30, measured 36.5 °C. Time difference is −30 minutes, correction is −0.05 °C, and adjusted temperature is 36.45 °C.