Your basal body temperature is your resting temperature on waking. After ovulation, progesterone raises it by about 0.2 to 0.5 °C (0.4 to 0.9 °F) and it stays higher until your next period. That rise confirms ovulation has already happened; it does not predict it. Charting your temperature every morning for a few cycles shows your own pattern.
Why temperature changes during the cycle
Before ovulation, in the follicular phase, temperature stays in a lower range. Once the ovary releases an egg, the corpus luteum produces progesterone, which slightly raises your body's set point. If you are not pregnant, progesterone falls before your period and temperature drops back. This two-level pattern is called a biphasic chart.
How to measure it correctly
- Use a basal thermometer that shows two decimal places.
- Measure right after waking, before you get up, talk or drink anything.
- Take it at about the same time every day, after at least three hours of sleep.
- Use the same method each time: mouth, vagina or rectum, never switching mid-cycle.
- Log the reading straight away and note anything unusual.
How to read your chart
- Look for a shift: at least three temperatures in a row higher than the six before them.
- Draw a line just above those six lower readings. This is often called the coverline.
- The day before the first higher reading is the most likely day of ovulation.
- Count the days of higher temperatures until your next period: that is your luteal phase.
| Pattern | What it can mean |
|---|---|
| Clear shift, high phase of 10 to 16 days | Ovulation likely happened |
| No clear shift | Possibly no ovulation that cycle, or measurement problems |
| Short high phase, under 10 days | A short luteal phase worth discussing with a professional |
| High temperatures for 18 days or more | Possible pregnancy: take a test |
A single cycle without a shift is not a reason to worry. Several in a row are worth discussing with a healthcare professional.
What can throw your readings off
- Illness or fever.
- Alcohol the night before.
- Short or broken sleep, or measuring at a very different time.
- Shift work, travel and time zone changes.
- Some medicines and hormonal contraception.
Mark these days as disturbed instead of deleting them, and do not use them to find the shift.
Combining temperature with other signs
Temperature only confirms ovulation afterwards. To see it coming, combine it with cervical mucus and LH tests. Our ovulation calculator gives you an estimate to start with.
Charting temperature in Bloom Private
Bloom Private lets you log basal body temperature next to cervical mucus, LH tests and cervical position, and see the chart for each cycle. If you choose to turn on Apple Health, the app can also write your temperature there. Temperature charting is not contraception, and the app is not a medical device.
Frequently Asked Questions
Usually about 0.2 to 0.5 °C (0.4 to 0.9 °F). It stays higher until your next period.
No. The rise comes after ovulation, so it confirms it. Cervical mucus and LH tests help you see ovulation coming.
One cycle without a clear shift can be due to measurement problems or a cycle without ovulation. If it happens several cycles in a row, talk to a healthcare professional.