Regular menstruation (also called eumenorrhea) lasts for a few days, usually 3 to 5 days, but anywhere from 2 to 8 days is considered normal. The average menstrual cycle is 28 days long from the first day of one menstrual period to the first day of the next.
Generally, it takes 28 days from the last time your period started for you to have your next period. This is especially true if you have a regular menstrual cycle. Some women though wait up to 35 days for their next period to start. You can find more information here: women.webmd.com
Your period can be so late that you can totally skip it. Late or skipped periods can be a result of many things including anxiety, stress, illness, medications and both physical and emotional exhaustion.