The luteal phase is the second phase of your cycle – after ovulation and before your period. This phase ends when your period begins. During the end of this phase, you may experience PMS symptoms, which you can track by using the #PMS feature – add #PMS to your Notes for any day, and the algorithm will inform you about upcoming PMS tailored to you and your cycle.
After the ovulation, progesterone is produced from the remains of the follicle that released the egg, the follicle is now called corpus luteum.
Corpus luteum is what produces progesterone, which the body needs to soften the endometrium (lining of the uterus). This makes it easier for the egg to attach if fertilized. If the egg isn’t fertilized, your period starts.
An increase of progesterone levels in the body also increases the temperature, which is what the algorithm uses to confirm both that you have ovulated and when you ovulated. If the egg is not fertilized, the corpus luteum stops producing progesterone after approximately 12-16 days and your temperature then drops below your cover line again, and your period will show up soon.
The luteal phase lasts roughly between 10-16 days, the average length is 14 days and is usually equally as long in every cycle. In the My cycle tab, you can see detailed information about your luteal phase, such as how long it usually lasts (the average length of your luteal phase) and your temperature variations. See this article to read more about the My Cycle tab and what you can learn from it.