The basal body temperature fluctuates daily, some days more than others. Changes in your routine can cause fluctuations as well – for example, changes in sleep, travel, and sickness can cause the basal body temperature to fluctuate. These factors can cause the Natural Cycles' algorithm to take longer to understand where you are in your cycle.
The app will indicate that you have "fluctuating temperatures" if it is having difficulties finding your ovulation day, due to a large spread among your temperatures (variation). Every now and then, the app may send you a warning in a message, about very high or low values. Please remember to take these messages into consideration – it's the app trying to help you.
Under the 'My Data' tab in your app, you may be told that your temperature variation is "unstable" (under 'My temperatures'). Your temperature variation is the number of degrees that your temperature is likely to change within each cycle. If it shows "unstable", please make sure to review our guidelines on how and when to measure your temperature. Most often, it may just be a small, simple, adjustment you may need to do to improve your measurements.
If you are working shifts please read more here.
If you have a baby or small children waking up at night we recommend you measure after your longest stretch of sleep or measure after you have had at least three hours of sleep. Read more about this here.
If you travel within different time zones and/or to a different climate, add the temperature as "excluded" the first 1-2 days so that your body gets used to the temperature change and then measure as usual. Read more about this here.
Do you have very few data points?
If you have a few data points (for instance if you've just started with Natural Cycles) and believe that your temperature fluctuates, keep measuring until you complete one cycle of measuring and adding data. A cycle begins on the first day of menstruation and ends when your next menstruation begins. The app will show you each cycle individually in the graph view. The graph is the best place to spot a fluctuation.
Are you measuring according to our guidelines?
Always measure before you get out of bed and as soon as you wake up. Read more here.
How can you see if your temperature is fluctuating?
In general, during your follicular phase (first period day to ovulation) your temperature should be below your cover line* - and roughly ranges between 35.75-36.40 °C (96.3-97.6 °F). In the luteal phase (ovulation to period), your body releases progesterone which raises your temperature to above your cover line - and roughly ranges between 36.40-36.90 °C (97.6-98.4 °F).
In the graph below, you will find an example of what can be considered temperature fluctuations throughout the different phases of a cycle.
Looking at the data for this user, we can see that the temperatures on Cycle Days 6, 8, and 11(follicular phase) rose above the cover line*: this would be considered a temperature fluctuation.
On Cycle Day 28 (luteal phase), the temperature suddenly dropped well below the cover line: this would also be considered a temperature fluctuation because this temperature is unusual for this phase of the cycle.
*The cover line is the average of all your temperature points throughout your cycles.