The menstrual cycle has four distinct stages: menstruation, the follicular phase, ovulation, and the luteal phase. A full cycle averages about 28 days, though anywhere from 21 to 35 days is normal. Each stage is driven by shifting hormone levels that prepare the body for a possible pregnancy, then reset when pregnancy doesn’t occur.
Stage 1: Menstruation
Your period is the most visible stage of the cycle and the one most people think of first. It happens because levels of two key hormones, estrogen and progesterone, drop sharply at the end of the previous cycle. Without those hormones to maintain it, the thickened lining of the uterus breaks down and sheds through the vagina as a mix of blood, tissue, and mucus.
Most periods last between three and seven days. The total blood loss is smaller than it feels: roughly two to three tablespoons over the entire period. Anything above about 80 milliliters (around five tablespoons) per cycle is considered heavy menstrual bleeding and worth bringing up with a healthcare provider. During this stage, energy tends to be lower, and cramping is common as the uterus contracts to help shed its lining.
Stage 2: The Follicular Phase
The follicular phase actually overlaps with menstruation. It starts on day one of your period and continues until ovulation, typically spanning the first 13 or 14 days of the cycle. The name comes from the follicles, tiny fluid-filled sacs in your ovaries where eggs mature.
Here’s what’s happening behind the scenes: your pituitary gland (a small structure at the base of the brain) releases a hormone that signals your ovaries to start developing several follicles at once. As the follicles grow, one becomes dominant and begins releasing large amounts of estrogen. That rising estrogen does two important things. First, it thickens the uterine lining from its post-period minimum up to about 12 to 13 millimeters, roughly half an inch, creating a nutrient-rich surface where a fertilized egg could implant. Second, it signals the brain to dial back the hormone that started the process, which causes the remaining non-dominant follicles to wither away.
For most people, the follicular phase is when they feel their best. Rising estrogen is linked to more energy, better sleep, improved mood, and a general sense of motivation or confidence. Bloating from your period typically fades as this phase progresses.
Stage 3: Ovulation
Ovulation is the shortest stage, lasting roughly 12 to 24 hours, though the fertile window around it stretches a few days longer. It’s triggered when the surge of estrogen from the dominant follicle causes a rapid spike in another hormone called LH. About 36 to 40 hours after that LH spike, the dominant follicle releases a mature egg into the fallopian tube.
Ovulation typically happens around day 14 in a 28-day cycle, but the timing varies widely from person to person and even cycle to cycle. Some people notice subtle signs: a slight rise in basal body temperature (measurable with a thermometer first thing in the morning), changes in cervical mucus that becomes clearer and more slippery, or a mild twinge of pain on one side of the lower abdomen. Basal body temperature tracking can confirm ovulation happened after the fact, but it can’t predict it in advance. At-home ovulation test strips work by detecting the LH surge in urine, which typically means ovulation will follow within 12 to 24 hours.
Stage 4: The Luteal Phase
After the egg is released, the now-empty follicle transforms into a temporary structure called the corpus luteum. Its sole job is to pump out progesterone, the hormone that shifts the uterine lining from “building mode” into “ready for pregnancy mode.” During this phase the lining thickens further, reaching 16 to 18 millimeters, and becomes more spongy and blood-vessel-rich.
The luteal phase lasts about two weeks in most people. If sperm fertilizes the egg and it implants successfully, the corpus luteum keeps producing progesterone to support the early pregnancy. If fertilization doesn’t happen, the corpus luteum starts breaking down roughly 10 days after ovulation. Progesterone and estrogen levels drop, the lining can no longer sustain itself, and menstruation begins. The cycle resets.
Why the Luteal Phase Feels Different
The high progesterone levels during this stage are responsible for many of the symptoms people associate with PMS. Common physical effects include breast tenderness, bloating, food cravings, headaches, constipation, and trouble sleeping. On the emotional side, mood swings, irritability, fatigue, sadness, and anxiety are all typical. These symptoms tend to peak in the final days before your period starts and ease once menstruation begins and hormone levels bottom out.
How Your Cycle Changes Over Time
The four stages stay the same throughout your reproductive years, but the timing and intensity shift. In the first few years after puberty, cycles are often irregular because the hormonal feedback loop is still maturing. Periods may come every three weeks one month and every six weeks the next, and that’s normal for adolescents.
Cycles tend to become more predictable through the twenties and thirties. Then, during perimenopause (the transition toward menopause, which can start in the early to mid-forties), ovulation becomes increasingly unpredictable again. You might notice your cycle length shifting by seven or more days compared to what’s been normal for you, a sign of early perimenopause. Flow can swing between unusually light and unusually heavy. If you go 60 days or more between periods, that’s typically a sign of late perimenopause, when ovulation is happening only sporadically.
Tracking your cycle, whether with an app, a calendar, or simply noting start dates, is one of the simplest ways to spot patterns, anticipate symptoms, and notice changes worth discussing with a provider. Even knowing which phase you’re in can help explain why your energy, sleep, or mood feels different from one week to the next.