During every cycle, the uterine lining (endometrium) gets thicker to prepare for a fertilized egg. This process occurs in most women that are of fertile age and not using any hormonal birth control. A period occurs if the released egg does not become fertilized and the lining of the uterus is shed. When you are on your period, you may need to use a tampon or a pad, and this should be marked as "Period" in the app.
Your period marks the start of a new cycle and is the 1st Cycle Day (CD1). Cycle Day 1 is shown in the app in the Today, Month, History, and Graph views by the period logo displayed on the days where you have added 'period.'
The length of your period may vary from cycle to cycle – on average, our Cyclers' periods last four days. You can also experience spotting during your cycle, which is not the same as your period. You can read more about spotting here.
In the 'My Cycle' (statistics) tab, you can see detailed information about your Period data, such as how long your bleeding usually lasts and how often you get your period (the average length of your cycle). You can read this article to read more about the 'My Cycle' tab and what you can learn from it.