BBT Calculator
Compare pre- and post-ovulation basal body temperature averages to confirm ovulation.
What is BBT?
Basal Body Temperature (BBT) — the temperature taken first thing on waking — drops slightly just before ovulation and rises about 0.4 °F (0.2 °C) afterward, sustained by progesterone. Tracking BBT over a full cycle reveals whether ovulation occurred and roughly when.
How is it calculated?
Difference = Average Post-Ovulation Temp − Average Pre-Ovulation Temp. A sustained shift of ≥ 0.4 °F (≥ 0.2 °C) over 3+ days is a reliable sign of ovulation.
Frequently Asked Questions
- How do I take BBT?
- On waking, before any activity, with a basal thermometer.
- Will BBT confirm ovulation?
- Retrospectively — the rise happens after ovulation.
- Is BBT enough for contraception?
- Not on its own — combine with other fertility-awareness signs.