A normal period (or normal menstruation) is different for every woman. Each month, one of your ovaries releases an egg. Meanwhile, your uterus gets ready to help your baby grow if that egg gets fertilized. If it does, you’re pregnant. If it doesn’t, your body sheds the lining of your uterus through your vagina. That’s your period. It happens, on average, every 28 days.

During a normal menstrual cycle, the lining of a woman's uterus sheds. This cycle is part of a woman's reproductive system and prepares the body for a possible pregnancy. It is also called a period, menses or cycle.

Most women have menstrual periods that last four to seven days. A woman's period usually occurs every 28 days, but normal menstrual cycles can range from 21 days to 35 days.

Examples of menstrual problems include:

• Periods that occur less than 21 days or more than 35 days apart

• Missing three or more periods in a row

• Menstrual flow that is much heavier or lighter than usual

• Periods that last longer than seven days

• Periods that are accompanied by pain, cramping, nausea or vomiting

• Bleeding or spotting that happens between periods, after menopause or following sex

Most girls get their first period between the ages of 10 and 15, but some get it earlier and some later.  A girl's monthly cycle is the number of days from the start of her period to the start of the next time she gets her period. You often hear this is a 28-day cycle. But 28 is just an average figure that doctors use. Cycle lengths vary — some are 24 days, some are 34 days. And a girl may notice that her cycles are different lengths each month — especially for the few years after she first starts getting her period. pregnancy test if you had unprotected sex and then missed your period. Just missing your period isn’t a foolproof way to know that you’re pregnant  a pregnancy test is the only way to find out for sure

Your periods are still considered regular if they come every 24 to 38 days. Your periods are considered irregular if the time between periods keeps changing and your periods come earlier or later.

A period that comes every cycle at exactly the same time is not the norm. Of course cycles are irregular when they’re first starting, as they’re coming to an end, and around the times of pregnancy and changes to contraceptive methods. But even outside of those times, slight variations in timing and symptoms are common. If you are stressed out during the first half of your cycle, for example, your ovulation may happen a couple of days later than usual. Progesterone (the hormone that’s dominant after ovulation) will then peak later in your cycle. This will cause certain symptoms (such as sore breasts) to happen later as well. Your period will also then be a couple of days late. While menstrual cycle irregularities usually aren't serious, sometimes they can signal health problems.