The average age for the onset of menses (menarche) is 12.7 years of age. The average age of cessation of menses is 51.4 years of age. The mean length of the menstrual cycle is 28 days, but this only occurs in 15% of females. The normal range of the menstrual cycle is 21 to 35 days. The average duration of menses is 3 to 5 days with an average blood loss of 30 to 60 ml, which is 1 to 2 ounces. Ovulation usually occurs on day 14, the first day of the menses being day 1.