Selected percentiles for the distribution of menstrual interval by age based on data from over 200,000 cycles. Longer intermenstrual intervals occur in females just after menarche and in the years preceding menopause.
Data from: Treloar AE, Boynton RE, Behn BG, Brown BW. Variation of the human menstrual cycle through reproductive life. Int J Fertil 1967; 12:77.