What the temperature chart can tell us

Every woman's cycle is unique — and so is her temperature chart. Once you start tracking your basal body temperature (BBT), you'll begin to notice patterns that reveal a great deal about your hormonal health, ovulation timing, and overall cycle rhythm. Here's a guide to reading your temperature curve and understanding what different patterns might mean.

A Typical BBT Curve

A classic BBT chart follows a bi-phasic pattern — two distinct phases separated by a clear temperature shift. In a 28-day cycle, ovulation typically occurs around days 12–13. You'll recognise it by a sustained rise in waking temperature of approximately 0.3°C. The phase before ovulation is called the follicular phase; the phase after is the luteal (or corpus luteum) phase, which lasts until menstruation begins. In a typical cycle, the luteal phase runs for around 12–16 days.

The Pre-Ovulation Temperature Dip

Some women notice a slight drop in temperature on the day just before ovulation (marked with an arrow in the chart above). This dip is caused by a surge in oestrogen immediately prior to the egg being released. While not everyone experiences it, when it does appear it can be a useful signal — particularly for those trying to conceive, as it often marks the most fertile day of the cycle.

Higher Than Usual Average Temperature

If your overall temperature readings are consistently higher than expected — even while still showing the typical bi-phasic rise after ovulation — this may be worth discussing with your doctor. A persistently elevated baseline temperature can sometimes be associated with an overactive thyroid (hyperthyroidism).

Other signs that may accompany hyperthyroidism include:

• Consistently long cycles (over 35 days)
• Short menstrual bleeds (under 3 days)
• General restlessness or nervousness
• Increased sweating

Only a doctor can diagnose thyroid conditions — but your temperature chart can be a helpful starting point for that conversation.

Lower Than Usual Average Temperature

A consistently low baseline temperature — particularly if your wake-up temperature regularly falls below 35°C — may indicate an underactive thyroid (hypothyroidism). Note that readings below 35°C are automatically excluded from Daysy and Lady-Comp's calculations and will show as a yellow or red day.

Other signs that may point to hypothyroidism include:

• Absent periods (amenorrhea)
• Persistently heavy periods
• Irregular cycles
• Cycles without ovulation (no temperature rise)
• A short luteal phase
• Significant day-to-day temperature fluctuations

Only a medical professional can confirm a thyroid diagnosis — but tracking your BBT gives you valuable data to share with your healthcare provider.

Out-of-Range Temperature Readings

Occasionally, a single measurement will appear significantly higher or lower than the surrounding days. These one-off outliers are usually caused by fever, disrupted sleep (too little or too much), alcohol consumption the night before, or an incorrect measurement technique. Both Daysy and Lady-Comp are designed to recognise and handle these outliers automatically — displaying a yellow or red day rather than letting a single unusual reading skew your fertility data.

Illness and Fever

A fever is generally defined as a body temperature of 38°C or above. If you're unwell, your BBT reading won't reflect your true hormonal baseline — so it's best to skip measurements until you're feeling better. As a general rule: if you wake up feeling sick, don't measure that day. Readings above 37.8°C are automatically excluded from the algorithm and won't affect your fertility calculations.

Have questions about your temperature chart or cycle patterns? We're happy to help — reach out to our team at info@periodwisdomboutique.com.au for a free cycle analysis.