Look for a biphasic shift: lower, relatively stable temperatures in the first half of the cycle, then a sustained jump of 0.3°C or more in the second half. Ovulation happened on the last low day or the first high day, and it is confirmed after 3 consecutive days of elevated temperature.
| Phase | Basal temperature |
|---|---|
| Before ovulation | 36.2°C to 36.5°C |
| After ovulation | 36.6°C to 37.1°C |
| The jump | 0.3°C to 0.5°C |
The jump comes from progesterone, produced by the corpus luteum after ovulation, and it holds the temperature up until the end of the cycle. On a chart this looks like two levels: a lower band in the first half, then a higher band in the second.
Before drawing conclusions, check whether something distorted a reading: a poor night's sleep, alcohol the night before, a cold or fever, a shift in timing, or sex before measuring.
If your temperature drops before 12 days after ovulation, a short luteal phase is confirmed. The luteal phase (between ovulation and menstruation) is nearly fixed at 12 to 14 days, and one shorter than 10 days is one of the most underdiagnosed causes of difficulty getting pregnant: an important conversation to bring to your doctor if you suspect it.
If there is a pregnancy, the temperature stays elevated past day 16 after ovulation: one of the earliest indirect hints of conception.
A basal temperature with no biphasic shift (no sustained jump) is one of the signs of an anovulatory cycle. An occasional one is normal, even in healthy women; several in a row deserve medical investigation.
You need at least 3 cycles to see patterns, and trusting a single chart is one of the things that does NOT work. The shape of the thermal curve varies from woman to woman, so the first 2 to 3 cycles are for learning yours. After that, once a month, compare the finished cycle against the average of the last 3 to 6: has ovulation been on the same day? Is the luteal phase consistent?
Reading the chart is part of Chapter 16 of Map to the Positive, in Station II (Attunement). The chapter also gives the correct method for taking your temperature, the factors that distort a reading, and why temperature works best combined with cervical mucus. Chapter 19, in the same station, adds the other signs that a cycle had no ovulation.
Take 30 days. If it does not give you more clarity than everything you have read for free so far, ask for a refund and you get every cent back. We cannot promise you a pregnancy. We can promise you will not be guessing.