Your Cycle

A story of hormones in flux

Fact: the female sex hormones that control your menstrual cycle naturally rise and fall throughout the month, as shown in the chart below. It's a dynamic process that repeats itself every 28 days, on average.

A few additional facts

Sex Hormone Levels Vary During the Menstrual Cycle

Sex Hormone Levels Vary During the Menstrual Cycle

Your cycle in close-up

Although the duration of each phase of the menstrual cycle can vary, the basic sequence of events does not.

Day 1: Your period

The first day of your period is considered Day 1 of your cycle. At this time, estrogen and progesterone, the 2 main types of reproductive hormones, are at low levels.

Day 5: One egg is selected

Inside the ovary, each egg is present within a “blister” called a follicle. As an individual egg develops, the follicle releases increasing amounts of estrogen.

Days 6-14: Preparing for ovulation

Toward the end of this stage, estrogen levels rise slowly, then more rapidly.

Around Day 14: Ovulation

The follicle surrounding the egg breaks open and the ovary releases the egg into the fallopian tube so it can be fertilized by sperm. The follicle remains in the ovary.

Days 15-28: After ovulation

After ovulation has occurred, levels of progesterone start to increase. If the egg that was released is not fertilized, estrogen and progesterone levels drop after approximately 2 weeks and the lining of the uterus gets ready to be shed. Your next period begins and the cycle starts again.


  1. Hallberg L, Hogdahl AM, Nilsson L, Rybo G. Menstrual blood loss—a population study. Variation at different ages and attempts to define normality. Acta Obstet Gynecol Scand. 1966;45:320-351.
  2. Fraser IS, Weisberg E, Minehan E, Johansson ED. A detailed analysis of menstrual blood loss in women using Norplant and Nestorone progestogen-only contraceptive implants or vaginal rings. Contraception. 2000;61:241-251.
  3. Hale GE, Manconi F, Luscombe G, Fraser IS. Quantitative measurements of menstrual blood loss in ovulatory and anovulatory cycles in middle- and late-reproductive age and the menopausal transition. Obstet Gynecol. 2010;115(2 pt 1):249-256.
  4. National Institute for Health and Clinical Excellence. 2007. Heavy Menstrual Bleeding. Clinical Guideline. London, UK: National Institute for Health and Clinical Excellence.