MoonstrateHow your cycle works
From Learn about your cycle. General wellness information, not medical advice. Sources.
The two phases and the moment between them
A menstrual cycle runs from the first day of one period to the first day of the next. Clinicians divide it into two phases, with ovulation between them.
The follicular phase starts on the first day of your period. It's named for follicles, the small fluid-filled sacs in the ovary where eggs mature. At the start, estrogen and progesterone are at their lowest and the lining of the uterus sheds, which is your period. Then a few follicles begin to grow, one takes the lead, and the estrogen it makes rises and rebuilds the lining.
Ovulation is the event that ends the follicular phase. When estrogen peaks, it triggers a surge of luteinizing hormone (LH), and that surge sets off the release of an egg from the leading follicle.
The luteal phase runs from ovulation to your next period. What's left of the follicle becomes the corpus luteum, which makes progesterone, along with some estrogen, to prepare the lining for a possible pregnancy. If no pregnancy begins, the corpus luteum breaks down, progesterone and estrogen fall, and that drop starts your next period.
The follicular phase is the part that varies most, from cycle to cycle and person to person, and it's most of why cycle lengths differ. The luteal phase tends to stay steadier, at about 11 to 14 days.
Next: Your Inner Seasons