In this article, we’ll cover what causes temperature fluctuations, how to spot them, and how you can adjust your measuring routine to improve fluctuations depending on which measuring device you use. Temperature fluctuations don’t affect Natural Cycles’ effectiveness as birth control, but you may get more Red Days (NC° Birth Control) or Brown Days (NC° Plan Pregnancy) which may reduce your satisfaction with the app.
Click into each of the sections listed below to access the information you are looking for:
- What causes temperature fluctuations?
- How can I see if my temperatures are fluctuating?
- What does a temperature curve with stable temperature variation look like?
- What can I do if my temperature fluctuates when measuring with a basal thermometer?
- What can I do if my temperature fluctuates when using the Oura Ring?
- What can I do if my temperature fluctuates when using the Apple Watch?
What causes temperature fluctuations?
Our body temperature fluctuates daily, some days more than others. However, if your temperatures fluctuate a lot and don’t follow the pattern of lower temperatures in the follicular phase and higher temperatures in the luteal phase, the NC° algorithm will struggle with detecting your ovulation.
Temperature fluctuations can be caused by a number of things related to your measuring routine, for example:
- The placement of the thermometer in your mouth
- How tightly or loosely the Oura Ring fits on your finger, or the Apple Watch on your wrist
- Alcohol consumption
- Illness
- Changes in sleep schedule (for those who measure with a thermometer)
- Some medications
You should exclude any temperatures that meet these criteria when they occur.
How can I see if my temperatures are fluctuating?
There are a few different ways to keep track of if your temperatures fluctuate during your cycles.
In-app messages
If your temperatures fluctuate a lot, the app may send you a message to let you know.
The app will indicate that you have fluctuating temperatures if it’s having difficulties finding your ovulation day due to significant temperature variations. Your temperature variation refers to how much your temperature is likely to change within each cycle phase. If the algorithm categorizes your temperatures as fluctuating, your average temperature variation is unstable, which means that your temperatures tend to vary a lot from one day to the next.
High temperature variation in your Cycle Insights
Under the Cycle Insights tab in your app, you can see if your temperature variations for each cycle phase are considered stable or unstable (by clicking on Follicular phase and Luteal phase). If it shows "unstable," this means that your temperatures are fluctuating.
Keeping an eye on your graph
We recommend looking at your graph frequently—preferably after each temperature—to help you understand what impacts your temperatures and how to reduce fluctuations. A single unusual temperature doesn’t mean that your temperatures are generally fluctuating, but if you notice it happening often, you can consider whether there’s something in your routine that could be causing it.
In the graph below, you’ll find an example of what temperature fluctuations throughout the different phases of a cycle can look like.
Looking at the data for this user, we can see that the temperatures on Cycle Days 4, 9, and 14 (follicular phase) rose above the cover line — this would be considered temperature fluctuations.
On Cycle Days 21 and 25 (luteal phase), the temperature suddenly dropped below the cover line — this is considered a temperature fluctuation because this temperature is unusual for this phase of the cycle.
What does a temperature curve with stable temperature variation look like?
While the average temperature in the follicular and luteal phases differs from person to person, your temperature follows a curve with lower temperatures in the follicular phase and higher temperatures in the luteal phase. Remember that it’s normal for the temperature to vary a bit from one day to the next, even if your temperatures are stable overall.
During your follicular phase (from first period day to ovulation), your temperature generally stays below your cover line.
In the luteal phase (from ovulation to the next period), your body releases progesterone, raising your temperature above the cover line.
When the temperature has risen enough to confirm ovulation, the most likely ovulation day gets calculated from the temperature curve. You can read more about ovulation detection here.
The graph above shows an example of a cycle with stable temperatures in each cycle phase – with lower temperatures during the follicular phase and higher temperatures in the luteal phase.
What can I do if my temperature fluctuates when measuring with a thermometer?
If your temperatures fluctuate a lot, the first thing to do is to review our measuring guidelines to see if you need to make any adjustments to your measuring routine. It may be that the thermometer placement in your mouth when measuring is incorrect, and it takes just a tiny, simple adjustment to improve your measurements.
If you’ve confirmed you’re measuring according to our measuring guidelines and your temperatures are still fluctuating, in general, temperature fluctuations can happen if you measure your temperature when:
- You have slept 2 hours more/less than usual (ex: on weekends)
- You have already snoozed
- Your partner, a child, or a pet woke you up close to your usual measuring time
- You have slept very poorly
- You feel hungover
- You have already gotten out of bed before measuring
- You feel sick
If any of the above applies to you, you should still measure your temperature in the morning (to stay in the routine), but you should exclude it when entering it into the app.
Please also refer to the articles listed below, depending on what applies to you:
- If you work shifts, please read more here.
- If you have a baby or small children who wake up at night, we recommend measuring after your longest stretch of sleep. Read more about this here.
- If you travel across different time zones, exclude your temperature on the first 1-2 days to give your body time to adapt. After that, you can continue to measure as usual. Read more about this here.
- If you often wake up at night, this article will help you identify the best time to measure.
- If you’re unsure when to exclude your temperature, this article may help.
- Do you have very few data points? If you only 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 entire 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 temperature fluctuations.
Do you measure with a basal thermometer? To track your temperature with Natural Cycle, you should only use a basal thermometer (with two decimals), an Oura Ring, or an Apple Watch. All other devices are not compatible with Natural Cycles.
What can I do if my temperature fluctuates when using the Oura Ring?
Fluctuating temperatures while wearing the Oura Ring could happen if:
- You’re wearing the Oura Ring on different fingers each night. To limit fluctuations, you should always wear the ring on the same finger of the same hand.
- You're feeling sick or hungover. In this case, you should exclude your temperature so that the algorithm does not take these temperatures into account.
- You are taking medication or hormones that affect your cycle and/or temperatures. We write more about this here.
- You tend to switch sleeping schedules from one day to the next without any specific pattern. This may affect the quality of your data and you can learn more about this here.
Another possible reason for fluctuations is that your Oura Ring does not fit properly on the finger. If your ring feels too tight or loose on your finger, please refer to this article from Oura for reference on the correct sizing of the ring. You can also reach out to the Oura team through this link so they can help ensure that you have the correct ring size on the correct finger.
From the data we’ve analyzed, we can share that fluctuating temperatures while wearing the Oura Ring are most often caused by rings that are too tight on the finger. Because hands tend to swell overnight, it's a good idea to aim for a slightly looser fit.
If your Oura Ring turns out to be too tight (or loose), we suggest that you wear it on a different finger (index, middle, or ring) on the same hand for at least a few weeks to see if this improves the fluctuations. We recommend that you pick a finger where the ring is not too tight but not too loose so that it rotates on its own.
What can I do if my temperature fluctuates when using the Apple Watch?
Fluctuating temperatures while wearing the Apple Watch can happen if:
- You're feeling sick or hungover. In this case, you should exclude your temperature so that the algorithm does not take these temperatures into account.
- You're taking medication or hormones that affect your cycle and/or temperatures. We write more about this here.
- You tend to switch sleeping schedules from one day to the next without any specific pattern. This may affect the quality of your data and you can learn more about this here.
- The watch is too tight or loose on your wrist. Your watch should fit snugly so there’s enough contact with the skin for the sensors to get a good temperature reading, but not too tight that it’s uncomfortable to wear overnight.
To help improve your data with Apple Watch:
- Try wearing the Apple Watch on your non-dominant hand.
- Try wearing a different band. From silicone to nylon, there are a range of band materials available. We recommend you choose a band that is both comfortable to wear and helps your watch fit snugly while you sleep.
- Try wearing your Apple Watch on your inner wrist. While many people wear their watch on the outer wrist, sleeping with the watch on the inner wrist can give you more stable temperatures due to increased blood flow in this area.