A woman’s cycle, or menstrual cycle, is a roughly monthly process in which the body prepares for pregnancy and then resets if pregnancy doesn’t occur. The average cycle lasts 28 days, but anything from 21 to 35 days is normal. It involves four distinct phases, each driven by shifting hormone levels that affect everything from energy and mood to body temperature and vaginal discharge.
The Four Phases
The cycle is divided into menstruation, the follicular phase, ovulation, and the luteal phase. Day 1 is the first day of your period, and the cycle ends the day before your next period starts. Here’s what happens in each phase.
Menstruation (Days 1 to 5, Roughly)
Your uterus sheds its lining because no fertilized egg implanted during the previous cycle. The flow contains blood, mucus, and tissue from the uterine lining. Most periods last between 3 and 7 days. Total blood loss during a normal period is under 60 milliliters, which is about 4 tablespoons. Anything over 80 milliliters is considered heavy menstrual bleeding and worth discussing with a provider.
The Follicular Phase (Days 1 to 14, Roughly)
This phase overlaps with menstruation and lasts about 13 to 14 days. Your brain signals the ovaries to start developing small fluid-filled sacs called follicles, each containing an immature egg. Usually only one follicle matures fully. At the same time, rising estrogen tells the uterine lining to thicken and rebuild, growing from a thin layer to about 12 to 13 millimeters before ovulation. Many people feel a boost in energy and mood during this phase as estrogen climbs.
Ovulation (Around Day 14)
When estrogen reaches a high enough level, it triggers a surge of hormones from the brain that causes the mature follicle to release its egg. This is ovulation, and it typically happens about two weeks before your next period. The egg survives for about 12 to 24 hours after release, making this the peak fertility window. Because sperm can survive inside the body for up to five days, the fertile window effectively stretches to about six days total: the five days before ovulation plus the day of ovulation itself.
The Luteal Phase (Days 15 to 28, Roughly)
After the egg is released, the empty follicle transforms into a structure that pumps out progesterone. This hormone keeps the uterine lining thick and spongy, preparing it for a fertilized egg. The lining reaches its maximum thickness of 16 to 18 millimeters during this phase. If the egg isn’t fertilized, progesterone drops, the lining breaks down, and your period begins, restarting the cycle.
What Drives the Whole Process
The cycle is controlled by a feedback loop between the brain and the ovaries. A small region in the brain releases a signal hormone in pulses, which tells the pituitary gland to produce two key hormones that act on the ovaries. One stimulates follicle growth and estrogen production. The other triggers ovulation once estrogen reaches a critical threshold. This rising estrogen actually amplifies the brain’s signal, creating a positive feedback loop that builds until it triggers the burst of hormones responsible for releasing the egg. It’s this feedback mechanism that makes the cycle, well, cyclical.
Physical Signs You Can Track
Your body gives observable clues about where you are in your cycle, which is useful whether you’re trying to conceive or simply want to understand your patterns.
Cervical mucus changes predictably throughout the cycle. Right after your period, discharge tends to be dry or sticky, with a pasty texture. As the follicular phase progresses, it becomes creamy and smooth, like yogurt. Just before and during ovulation, it turns wet, stretchy, and slippery, resembling raw egg whites. This consistency helps sperm travel through the reproductive tract. After ovulation, it returns to thick and dry. If you notice the egg-white texture, you’re at your most fertile.
Basal body temperature (your temperature first thing in the morning before getting out of bed) also shifts. After ovulation, progesterone causes a small but measurable rise, typically between 0.4°F and 1°F. The increase confirms that ovulation has already happened, so it’s more useful for confirming patterns over several months than for predicting fertility in real time.
PMS and Luteal Phase Symptoms
The luteal phase is when premenstrual symptoms show up. PMS is diagnosed when at least one emotional symptom (irritability, mood swings, anxiety) and one physical symptom (bloating, breast tenderness, joint pain) appear after ovulation and resolve shortly after your period starts. These symptoms are tied to the rise and fall of progesterone and estrogen in the second half of the cycle.
For a smaller number of people, premenstrual symptoms are severe enough to interfere with work, relationships, or daily functioning. This is classified as premenstrual dysphoric disorder (PMDD), which involves at least five symptoms in the final week before menstruation, including marked mood swings, irritability, a feeling of being overwhelmed or out of control, and physical symptoms like breast swelling or muscle pain. PMDD is distinct from general depression or anxiety because it follows a strict cyclical pattern, improving within days of your period starting and largely disappearing the week after.
How the Cycle Changes Over a Lifetime
Cycles aren’t static. In the first few years after periods begin (typically between ages 10 and 16), cycles are often irregular as the hormonal feedback loop matures. By the late teens and twenties, most people settle into a more predictable pattern, though cycle length can still vary by a few days from month to month.
In the years leading up to menopause, a transition called perimenopause, estrogen and progesterone levels become increasingly unpredictable. You may notice your cycle getting shorter or longer, your flow becoming heavier or lighter, or skipping periods entirely. If your cycle length shifts by seven or more days consistently, that’s often an early sign of perimenopause. Going 60 or more days between periods suggests you’re in the later stage. This transition typically begins in the mid-40s but can start earlier, and it ends when you’ve gone a full 12 months without a period, which marks menopause.
What Counts as Irregular
A cycle is generally considered irregular if it consistently falls outside the 21-to-35-day range, if your period lasts longer than 7 days, or if the gap between cycles varies widely from month to month. Occasional irregularity is common and can be caused by stress, significant weight changes, intense exercise, or illness. Persistent irregularity can signal conditions like polycystic ovary syndrome, thyroid disorders, or issues with the uterine lining. Tracking your cycle for a few months, even with a simple calendar or app, gives you a baseline to notice meaningful changes.