09/12/2025
*MENSTRUAL PERIOD INTERVAL (CYCLE LENGTH)*
The menstrual cycle interval is the number of days from Day 1 of one period to Day 1 of the next period.
NORMAL CYCLE LENGTH
-21 to 35 days in adults
-21 to 45 days in adolescents (first few years after menarche)
HOW TO COUNT IT
-Day 1 = first day of full menstrual bleeding (not just spotting)
-Count until the day before the next period starts
COMMON VARIATIONS
-Cycles may vary by ± 2–3 days and still be normal.
-Stress, weight changes, illness, travel, or hormonal fluctuations may shift the interval.
ABNORMAL INTERVALS
Cycle Length Meaning
< 21 days Polymenorrhea (too frequent periods)
> 35 days Oligomenorrhea (infrequent periods)
> 90 days Needs evaluation (possible PCOS, thyroid issues, pregnancy, etc.)