Normal Period Timing? Every month, your entire body prepares to get pregnant. Your ovaries release an egg. Hormones rise and fall. This is your menstrual cycle. It starts on the first day of your last period and ends on the first day of your next period. Though the average cycle is 28 days long, anything between 21 and 45 days is considered normal. That's a 24-day difference. For the first year or two after menstruation begins, women tend to have longer cycles that don't start at the same time every month. Older women often have shorter, more consistent cycles. If you're on birth control pills or have an IUD, it can change the timing of your period. Ask your doctor what's normal for your form of contraception. How long your period lasts also varies. The time from the first sign of blood to the last is usually in the 3-to-5-day range. Any length from 2 days to a week is normal for a period.