My temperature fluctuates – why, and what can I do about this? – Customer Support | Contact Us | Natural Cycles

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What causes temperature fluctuations?

Body temperature fluctuates daily, some days more than others. However, if your temperatures fluctuate a lot and do not follow the pattern of lower temperatures in the follicular phase and higher temperatures in the luteal phase, this may mean that something about your measuring routine should be adjusted.

Sometimes, temperature fluctuations can be because of adjustments that need to be made to your measuring routine, like the placement of the thermometer in your mouth or how tight or loose the Oura Ring is on your finger or the Apple Watch is on your wrist. To fix this, you will need to adjust how you use your device. We cover how to address this below, depending on your measuring device.

However, temperature fluctuations can sometimes be due to other factors like alcohol consumption, changes in sleep, sickness, and some medications, which are all known to have the ability to impact your temperature. You should exclude any temperatures that meet this criteria when they occur.

Generally speaking, we recommend looking at your graph frequently, preferably after each temperature to help you understand what impacts your temperatures and how to reduce fluctuations.

How can you see if your temperature is fluctuating?

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.

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 app will indicate that you have fluctuating temperatures if it is having difficulties finding your ovulation day due to significant temperature variations. Your temperature variation is the number of degrees that your temperature is likely to change within each cycle phase. A single unusual temperature does not mean that your temperatures are fluctuating. If the algorithm categorizes your temperatures as fluctuating, your average temperature variation is unstable, which means that your variation is high.

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 scrolling down to Follicular phase and Luteal phase). If it shows "unstable", this means that your temperatures are fluctuating.

If your temperatures fluctuate a lot, the app may send you a message to let you know. Please remember to consider these messages – the app is trying to help you.

What does a graph with fluctuating temperatures look like?

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 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 can I do if my temperature fluctuates when measuring with a thermometer?

If your temperature fluctuates a lot, the first thing to do is to review our measuring guidelines and re-assess your measuring routine to see if you need to make adjustments. Most often, 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 waking up at night, we recommend you measure 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 identify the best time for you 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? You should only use a basal thermometer (with two decimals), an Oura Ring or an Apple Watch to track your temperature with Natural Cycle. 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 these temperatures are not taken into account by the algorithm.
You are taking medication/hormones that affect your cycle/temperatures. We write more about this here.

Your Oura Ring does not fit properly on the finger, so 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. If in doubt, 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 is a good idea to aim for a slightly looser fit.

If it turns out that your Oura Ring was too tight (or loose), we’d suggest that you wear the ring 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 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 could happen if:

You're feeling sick or hungover. In this case, you should exclude your temperature so that these temperatures are not taken into account by the algorithm.
You are taking medication/hormones that affect your cycle/temperatures. We write 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 with the 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.

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