Basal Body Temperature & Ovulation Detection
Your basal body temperature (BBT) is your body's resting temperature, measured right after waking, before you get out of bed. After ovulation, progesterone causes a shift of 0.3–0.5°C that persists until your next period. Enter today's temperature and cycle day to analyze whether the pattern indicates ovulation.
When to use this calculator
- You want to confirm whether you ovulated this cycle.
- You use the symptothermal method to plan or prevent pregnancy.
- You want to confirm ovulation after a positive LH test.
- You track fertility and want to analyze your temperature pattern.
- You suspect you're not ovulating and want data to discuss with your doctor.
Example: 36.7°C on cycle day 16
- Temperature: 36.7°C.
- Cycle day: 16.
- Interpretation: elevated temperature suggests post-ovulation.
- Phase: early luteal phase.
How it works
1 min readHow Basal Body Temperature Works
Before ovulation, your basal body temperature is lower (~36.1–36.4°C). After ovulation, progesterone raises it by ~0.3–0.5°C (~36.4–36.8°C). This shift creates a biphasic pattern.
How to Measure It Correctly
1. Measure immediately upon waking, before getting out of bed, talking, or using the bathroom.
2. Use a basal body temperature thermometer (with 0.01°C precision).
3. Measure in the same location every time (mouth, vaginal, or rectal).
4. Measure at the same time each morning (±30 minutes).
5. Record your readings in a chart or app.
Interpreting Your Pattern
| Pattern | Meaning |
|---|---|
| Biphasic (low → high) | Ovulation confirmed |
| Monophasic (no change) | Possible anovulatory cycle |
| High > 16 days | Possible pregnancy |
| Sharp drop | Period coming soon |
Important Limitations
Related Calculators
Frequently asked questions
What's a normal basal body temperature?
Before ovulation, BBT typically ranges from 36.1 to 36.4°C (97 to 97.5°F). After ovulation, it rises to 36.4–36.8°C (97.5–98°F) or higher. Every woman's baseline is different—track your own pattern, not absolute numbers.
How much does BBT rise after ovulation?
BBT typically rises 0.3–0.5°C (0.5–1°F). The increase may happen gradually over 1–2 days or suddenly. A sustained rise for 3+ consecutive days confirms ovulation has occurred.
What if my temperature doesn't rise?
A cycle without a clear temperature shift may indicate an anovulatory cycle (a cycle without ovulation). Occasional anovulatory cycles are normal, but if this happens frequently, talk to your doctor.
Can elevated basal body temperature indicate pregnancy?
Yes. If your temperature remains elevated for more than 16 days (longer than a typical luteal phase), it's a strong sign of pregnancy. Confirm with a pregnancy test.
What thermometer should I use?
A basal body temperature thermometer is recommended because it displays to 0.01°C precision (like 36.45°C). Standard thermometers show only one decimal place and may miss the small 0.3°C shift.
What can affect my basal body temperature reading?
Alcohol, sleeping fewer than 3 hours, fever, certain medications, and high stress can all raise your BBT. Mark these factors on your chart so you know which readings need context.
Is BBT alone reliable for contraception?
Basal body temperature alone is not reliable for birth control. Combined with cervical mucus observation (the symptothermal method), effectiveness improves—but it requires careful daily tracking.
How long does BBT stay elevated after ovulation?
Your temperature typically stays elevated for about 12–14 days (the luteal phase) before dropping as your period approaches. If it stays high beyond 16 days, pregnancy may be the cause.
Why measure BBT immediately upon waking?
Any activity—even getting out of bed—raises your body temperature. BBT is your lowest resting temperature, so measuring before any movement gives the most accurate reading for ovulation tracking.