What is the duration of a normal menstrual cycle?

24 - 32 days. Gynecological textbooks say that cycles between 24 and 32 days are normal. The count starts on the day a woman starts her period, which can be just slight spotting, before normal flow sets in and stops the day before the next period starts. Ovulation is length of cycle minus 14 days. The second half of the cycle after ovulations needs to last for 2 weeks.