Basal Body Temperature Calculator
Log your morning BBT readings to detect ovulation, identify cycle phases, and track hormonal patterns — in Celsius or Fahrenheit.
BBT Tracker & Analyzer
Ovulation detection & cycle phase analysis
Normal pre-ovulation: 36.1–36.4°C
Basal Body Temperature rises by 0.2–0.5°C (0.4–0.9°F) after ovulation due to the thermogenic effect of progesterone. By charting daily BBT, you can confirm ovulation has occurred and identify your follicular and luteal phases with precision.
Measure immediately upon waking, before getting up or drinking anything. Use the same thermometer each day, at the same time (±30 min). A 3-day sustained rise above the coverline confirms ovulation.
How to Read Your BBT Chart
The coverline is drawn 0.05°C above the highest temperature in the last 6 days before the rise. Three consecutive readings above the coverline confirm ovulation. The fertile window is typically the 5 days before ovulation and the day of ovulation itself.
| Phase | Duration | Normal BBT (°C) | Normal BBT (°F) |
|---|---|---|---|
| Menstruation | Days 1–5 | 36.1–36.4°C | 97.0–97.5°F |
| Follicular (pre-ovulation) | Days 6–13 | 36.1–36.4°C | 97.0–97.5°F |
| Ovulation (thermal shift) | Day 14 ±3 | Rise ≥0.2°C | Rise ≥0.4°F |
| Luteal (post-ovulation) | Days 15–28 | 36.5–37.0°C | 97.7–98.6°F |
| Possible pregnancy | 18+ days elevated | >37.0°C sustained | >98.6°F sustained |
Sympto-Thermal Method: Combine BBT with cervical mucus observation for the most reliable natural family planning. BBT alone only confirms ovulation retrospectively — it cannot predict it in advance.