What is the cover line and how is it determined?
In your graph, you will see a thicker, gray, horizontal line. This is your cover line, which helps you visualize the temperature ranges that are associated with the follicular phase and the luteal phase, as well as the temperature shift that indicates ovulation.
The cover line represents the average of all your temperature points throughout your cycles. It also takes into account the average temperature and variations in the two phases of your cycle (the follicular and luteal phases). As you continue to measure and add more temperature data, the cover line will adjust accordingly.
Why don’t I have a cover line?
When you first get started with Natural Cycles, it can take some time before the algorithm gets to know you, so you may not see your cover line right away. In general, it can take between a few days up to a full cycle before the cover line is shown. If you don’t see it yet, just keep measuring according to our guidelines, and you’ll soon see your cover line!
Your cover line may also disappear if you change measuring devices (for instance, if you switch from measuring with an oral thermometer to the Oura Ring or Apple Watch). That’s because different devices may measure differently, and while both devices are accurate, it’s to be expected that the absolute values will differ. The algorithm will need to establish a new cover line based on the temperatures from your new measuring device. Once this is done, your cover line should return!
Why is the cover line important?
The graph and the cover line can be helpful tools to keep track of your temperatures and gain a better understanding of how your measuring habits impact your temperatures.
When looking at your graph, you want to make sure that the temperature variations within each cycle phase are as small as possible – this makes it easier for the algorithm to confirm your ovulation.
In general, your temperature will be lower and stay below your cover line during your follicular phase. During the luteal phase, your temperatures are higher and will generally stay above the cover line.
If you notice that your temperature tends to fluctuate above and below the cover line throughout your cycle without following a specific pattern, something may need to be adjusted in your measuring routine. You can read more about temperature fluctuations and how to avoid them here. If your temperature variations are generally stable and you notice that a temperature is unusually high or low for the cycle phase that you are in at the time, it’s a good idea to try and consider if something was different in your routine that day and if the temperature should be excluded.