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Predict future menstrual periods, track cycle regularity, map follicular and luteal phases, and identify symptoms of premenstrual syndrome (PMS).
Average Cycle Length = Sum of Historical Cycle Days / Number of Cycles Logged.Next Period Start = Last Period Start Date + Average Cycle Length.Follicular Phase = Day 1 to Day (Cycle Length - 14); Luteal Phase = Day (Cycle Length - 13) to Day (Cycle Length).PMS Window = Next Period Start Date - 7 Days through Day 1 of Menses.A normal menstrual cycle lasts between 21 and 35 days in adult women (average 28 days). Natural cycle variance of ±2 to 4 days from month to month is common and healthy.
The follicular phase (time from period start to ovulation) varies based on stress, sleep, travel, and nutrition. The luteal phase (time from ovulation to next menses) is biologically fixed at 12 to 16 days (typically 14 days).
Cycles consistently shorter than 21 days, longer than 35 days, or varying in length by more than 7 to 9 days indicate irregular menstruation, warranting screening for PCOS or thyroid dysfunction.
PMS is triggered by the rapid decline of estrogen and progesterone levels during the final week of the luteal phase if fertilization does not occur, altering central neurotransmitters like serotonin.