🌡️ BBT Calculator (Basal Body Temperature)
Enter your baseline basal temperature and today’s reading to see if the shift is large enough to suggest ovulation has occurred.
The BBT shift method
Basal body temperature (BBT), taken first thing in the morning before getting out of bed, typically rises slightly after ovulation due to increased progesterone. Charting this small but consistent rise is a widely used natural way to confirm that ovulation has likely already occurred in a cycle.
The 3-over-6 coverline rule
A common charting rule looks for a temperature that is at least 0.4°F (about 0.2°C) higher than the average of the previous six low readings, sustained for three consecutive days, to confirm a genuine post-ovulation shift rather than day-to-day noise. This calculator checks a single reading against that threshold as a quick reference.
- Threshold: ~0.4°F (0.2°C) above your recent baseline average
- BBT confirms ovulation has happened; it does not predict it in advance
This tool is for general educational cycle-awareness purposes only and is not a method of contraception or a medical diagnosis. Illness, alcohol, sleep disruption and thermometer inconsistency can all affect readings; consult a healthcare professional for fertility guidance.