symptom-guides

Basal Body Temperature Throughout the Menstrual Cycle: What

Basal body temperature rises 0.2–0.5°C after ovulation due to progesterone. It confirms ovulation happened — it doesn't predict it. Here's how to track it

Basal body temperature charting is the oldest modern fertility awareness tool, developed systematically by Dr. Wilhelm Hillebrand in Germany in the 1930s and formalized into clinical practice through the 1950s. It works because progesterone is thermogenic — it raises resting body temperature measurably and consistently after every ovulation. That simple biology makes BBT a reliable ovulation confirmation signal. The Two Phase Pattern A typical ovulatory cycle produces a clearly biphasic BBT pattern: Follicular phase (before ovulation): Temperatures are lower — typically 36.1–36.5°C (97.0–97.7°F) Minor daily variation is normal (0.1–0.2°C) Some people see a slight dip on the day of ovulation itself (the LH surge dip) No progesterone is present, so no thermogenic elevation After ovulation: The corpus luteum begins producing progesterone Progesterone activates thermoreceptors in the hypothalamus, raising the body's temperature set point by 0.2–0.5°C The rise may be abrupt (next day jump) or gradual (rising over 2–3 days) Temperatures remain elevated through the entire luteal phase (10–16 days) On the last 1–2 days of the luteal phase, temperatures typically drop before or at the onset