Basal body temperature (BBT) is your resting temperature on waking. After ovulation, progesterone raises it slightly, usually by about 0.2 to 0.5°C (0.4 to 1°F), and it stays higher until your next period. BBT confirms ovulation after the fact, so many people combine it with LH tests that predict ovulation ahead of time. Measure at the same time every morning before getting up, or use a wearable that tracks overnight temperature.
BBT is a low-cost way to learn your cycle’s pattern.
How to measure
- Use a BBT thermometer with two decimal places.
- Measure at the same time each morning before getting up.
- Record in an app or chart.
- Note disruptions such as illness or late nights.
Reading your chart
| Phase | Temperature |
|---|---|
| Before ovulation | Lower |
| After ovulation | Shifts up and stays higher |
| Before period | Drops |
| Pregnancy | Can stay elevated |
Combine methods
- LH tests predict ovulation.
- BBT confirms it.
- Cervical mucus observations add context.
Store your data safely with a privacy-focused app. Browse fertility and ovulation.
Common questions
Can BBT predict ovulation?
Not in the same cycle. It shows ovulation already happened. Patterns over several cycles can help you anticipate it.
What affects BBT?
Illness, alcohol, poor sleep, travel, shift work and measuring at different times.
Are wearable temperature trackers accurate?
Many track skin temperature overnight and estimate trends. Check each device's regulatory status and claims.