Frequency of menses

The normal frequency of onset of menstrual periods is from 24 to 38 days, based on large databases and using the 5^th to the 95^th percentiles.
(A) The top panel demonstrates an individual with a 27-day cycle that is "normal."
(B) The middle panel is a cycle length of 44 days, outside the normal range (infrequent).
(C) The bottom panel depicts a cycle length of 22 days and is, therefore, defined as being "frequent."