The menstrual cycle is the roughly monthly process your body goes through to prepare for pregnancy. It involves a coordinated sequence of hormonal shifts that trigger changes in your ovaries and uterus, and it repeats from puberty until menopause. A typical cycle lasts about 28 days, though anywhere from 21 to 35 days is normal. The cycle has four distinct phases, each driven by different hormones and producing noticeable changes in your body.
The Four Phases of the Cycle
The menstrual cycle is divided into four phases: menses, the follicular phase, ovulation, and the luteal phase. These phases overlap slightly, and the timing shifts from person to person, but the sequence is always the same.
Menses (days 1 to 5): This is your period. Because no pregnancy occurred in the previous cycle, the thickened lining of your uterus sheds through your vagina as blood and tissue. Bleeding typically lasts 4 to 5 days, and most people lose about 2 to 3 tablespoons of blood total. Bleeding for more than 7 days, or losing roughly double that amount, is considered heavy menstrual bleeding.
Follicular phase (days 1 to 13): This phase starts on the same day as your period and runs until ovulation. Your pituitary gland, a small structure at the base of your brain, releases a hormone that stimulates your ovaries to start developing eggs. Between 11 and 20 eggs begin maturing inside tiny fluid-filled sacs called follicles, but only one will fully mature. That dominant follicle pumps out rising levels of estrogen, which signals your uterine lining to thicken and prepare a nutrient-rich environment in case a fertilized egg needs to implant.
Ovulation (around day 14): A sharp surge of luteinizing hormone from the pituitary gland triggers the mature follicle to release its egg from the ovary. The ovulatory phase itself is brief, lasting only about 16 to 32 hours and ending once the egg is released, roughly 10 to 12 hours after the hormone surge. Once free, the egg survives for less than 24 hours, which is why the window for fertilization each cycle is so narrow.
Luteal phase (days 15 to 28): After releasing the egg, the empty follicle transforms into a temporary structure that produces progesterone. This hormone further prepares the uterine lining for pregnancy, making it spongy and rich with blood vessels. If the egg isn’t fertilized, that structure begins to break down about 10 days after ovulation. Progesterone drops, the uterine lining loses its support, and menstruation begins, restarting the cycle.
How Hormones Drive the Cycle
Four hormones do most of the work. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are produced by the pituitary gland and act on the ovaries. FSH kicks off follicle development in the first half of the cycle. LH surges mid-cycle to trigger ovulation. These two hormones also stimulate the ovaries to produce the other two key players: estrogen and progesterone.
Estrogen dominates the first half of your cycle. It thickens your uterine lining and prepares your breasts and reproductive tract for a possible pregnancy. Progesterone takes over after ovulation, maintaining the lining and creating conditions that would support an embryo. When progesterone drops at the end of the luteal phase, it’s the direct trigger for your period to start. This hormonal rise and fall is why many people notice predictable physical and emotional changes at specific points in their cycle.
Changes You Can Track
One of the most reliable physical signs of where you are in your cycle is cervical mucus, the fluid produced by your cervix. In the days after your period, it tends to be dry or tacky and white. As you move toward the middle of your cycle, it becomes creamy and cloudy, similar to yogurt. Right around ovulation, days 10 to 14 in a typical cycle, it turns clear, slippery, and stretchy, often compared to raw egg whites. This is when you’re most fertile. After ovulation, it dries up again and stays that way until your next period.
This pattern is useful whether you’re trying to get pregnant or simply want to understand your body’s rhythms. Home ovulation tests work by detecting that mid-cycle surge in luteinizing hormone in your urine, offering another way to pinpoint your fertile window.
When the Cycle Starts and Ends
Most people get their first period around age 12, though the median has shifted slightly earlier over recent decades. CDC data shows the median age dropped from 12.1 years in 1995 to 11.9 years by 2013 to 2017. Starting anywhere between ages 9 and 16 falls within the normal range.
Menstrual cycles continue until menopause, which typically occurs between ages 45 and 55. In the years leading up to menopause, cycles often become irregular as hormone levels fluctuate and eventually decline. Once you’ve gone 12 consecutive months without a period, menopause is confirmed and the cycle has ended permanently.
What Makes Cycles Irregular
Plenty of everyday factors can throw off your cycle’s timing or flow. Stress is one of the most common culprits, because the hormones your body releases under stress can interfere with the signals between your brain and ovaries. Gaining or losing a significant amount of weight can have the same effect, as can extreme exercise routines that drop your body fat very low. This is particularly common in long-distance runners, dancers, and gymnasts. Changing your birth control method or starting a new workout routine can also shift your cycle temporarily.
If you want to keep your cycle regular, gradual changes tend to be easier on your body than dramatic ones. Crash diets, sudden intense exercise programs, and chronic sleep deprivation all create the kind of physiological stress that disrupts hormonal signaling. Moderate exercise, consistent sleep, and steady nutrition support a more predictable cycle. That said, some variation from month to month is completely normal. A cycle that’s a few days shorter or longer than usual isn’t cause for concern on its own. Cycles that consistently fall outside the 21 to 35 day range, or periods that suddenly become much heavier or more painful, are worth paying attention to.