My Monthly Cycle

The period before your period.

You might not realize it, but there's a lot going on in your body long before your period starts:

  • In the first half of your menstrual cycle, levels of a female hormone, estrogen, begin to climb. Can you say mood swings?
  • As estrogen rises, the lining of the uterus (or womb) grows and thickens. The lining of the womb is what nourishes an embryo if a woman becomes pregnant.
  • During the same time that the lining is growing, an egg (or ovum) in one of the ovaries starts to mature.
  • Midway through the cycle, at about day 14 (for an average 28-day menstrual cycle), the egg leaves the ovary. This is called ovulation.
  • It's around ovulation that a woman is most able to get pregnant.
  • Since every woman's cycle is unique, the time of ovulation can vary. But, on average, a woman is most fertile during the 3 days before ovulation, on the day of ovulation, and 12 to 24 hours after she ovulates.

Here Comes Your Period.

Each month, your menstrual cycle repeats:

  • The egg leaves the ovary and travels through the fallopian tube toward the uterus.
  • Pregnancy can happen if the woman's egg is fertilized by a man's sperm and the fertilized egg attaches to the uterine wall.
  • During this time, progesterone levels increase to help prepare the uterine lining for pregnancy.
  • If the egg isn't fertilized, hormone levels decrease, the thickened lining of the uterus is shed, and voila! Your period starts.
Menstrual cycle chart

Most women's periods are pretty predictable, starting every 21 to 35 days in adults, and every 21 to 45 days in teens. The average monthly menstrual cycle lasts around 28 days. A full menstrual cycle is counted from day 1 of your current period until the first day of your next period (Day 1 to Day 1).

It's important to know that even if you think your period is "regular," it can change from month to month. Most periods last between 3 and 5 days. But it's still considered normal to have a period that lasts anywhere from 2 to 7 days. Be sure to talk to your doctor if you have any questions or concerns about your cycle.