Your menstrual cycle has three main phases: the follicular phase (which includes your period), the ovulatory phase, and the luteal phase. A full cycle typically lasts between 24 and 38 days, though the “textbook” 28-day cycle is more of a rough average than a rule. Only about 87% of people fall within that 24-to-38-day range, and plenty of cycles land somewhere other than day 28.
Each phase is driven by shifting hormone levels that prepare your body for a potential pregnancy, then reset when one doesn’t occur. Here’s what happens in each phase, how long it lasts, and what you can expect to feel.
Menstruation: Days 1 Through 5
Your cycle starts on the first day of bleeding. This happens because estrogen and progesterone both drop sharply at the end of the previous cycle, signaling your uterus to shed its lining. That lining exits as menstrual blood over the course of roughly 3 to 7 days.
Most periods involve less than 45 mL of actual blood, which is about three tablespoons. Anything under 60 mL is considered normal. If you’re regularly soaking through a pad or tampon every hour for several hours, or passing large clots, that may signal heavier-than-normal bleeding worth looking into. Periods over 100 mL of blood loss are classified as excessive.
The Follicular Phase: Building Up Again
The follicular phase technically begins on day 1 of your period and runs until ovulation, so it overlaps with menstruation. After your period ends, this phase is when your body actively prepares its next egg. It ranges from 14 to 21 days total, making it the most variable part of the cycle. If your cycle is longer or shorter than average, this phase is usually the reason.
Here’s the chain of events: your pituitary gland (a small structure at the base of your brain) releases follicle-stimulating hormone, or FSH. FSH activates your ovaries to start developing follicles, which are tiny fluid-filled sacs where eggs mature. Several follicles begin growing, but one becomes dominant and starts pumping out estrogen. That rising estrogen does two things. First, it thickens the lining of your uterus from its post-period minimum up to about 12 to 13 millimeters, creating a cushion where a fertilized egg could implant. Second, it signals your pituitary gland to dial back FSH production, which causes the non-dominant follicles to wither away.
During this phase, many people notice increased energy and a more stable mood compared to the days right before or during their period. That tracks with the steady climb in estrogen.
Ovulation: The 24-Hour Window
Ovulation is the shortest phase, lasting roughly 12 to 24 hours. It typically occurs between day 12 and day 16 of a 28-day cycle. The trigger is a sudden surge in luteinizing hormone (LH), which causes the dominant follicle to rupture and release a mature egg into the fallopian tube.
The egg itself survives for only 12 to 24 hours after release. Because sperm can live inside the reproductive tract for up to five days, the fertile window extends a few days before ovulation as well. Estrogen, LH, and testosterone all peak around this time, which is why some people feel a boost in energy or libido at mid-cycle.
Signs That Ovulation Is Happening
Your body offers a couple of observable clues. In the days leading up to ovulation, cervical mucus increases noticeably and becomes thin, slippery, and stretchy (often compared to raw egg whites). Right after ovulation, it decreases and turns thicker. Your basal body temperature, the lowest temperature your body reaches at rest, also rises by about 0.5 to 1°F after ovulation and stays elevated through the rest of the cycle. The catch is that this temperature shift only confirms ovulation after it has already happened, so it’s more useful for tracking patterns over several months than for predicting ovulation in real time.
The Luteal Phase: The Premenstrual Stretch
After the egg is released, the now-empty follicle transforms into a structure called the corpus luteum. This structure produces progesterone, the hormone that dominates the second half of your cycle. Progesterone continues to thicken and stabilize the uterine lining, which grows to 16 to 18 millimeters at its peak, preparing it for a potential embryo.
The luteal phase lasts about 14 days and is the most consistent part of the cycle from person to person. If fertilization doesn’t occur, the corpus luteum breaks down, progesterone and estrogen levels plummet, and the uterine lining begins to shed. That brings you back to day 1.
Rising progesterone is responsible for many of the symptoms people associate with PMS. Common ones include:
- Breast tenderness
- Bloating
- Acne breakouts
- Mood changes and irritability
- Increased appetite or cravings
- Fatigue and brain fog
These symptoms tend to peak in the last few days before your period and resolve once bleeding begins and hormone levels reset.
Why Your Cycle Length Varies
The 28-day cycle gets all the attention, but data from the Apple Women’s Health Study at Harvard, which tracked tens of thousands of participants, shows that cycle length varies widely. A “normal” cycle falls anywhere between 24 and 38 days. About 13 out of every 100 people have a median cycle length outside even that broad range.
Most of the variation comes from the follicular phase. Stress, illness, travel, weight changes, and sleep disruptions can all delay or accelerate follicle development, shifting ovulation earlier or later. The luteal phase, by contrast, stays close to 14 days regardless of overall cycle length. So if your cycle suddenly runs long, it almost always means ovulation was delayed, not that something went wrong after it.
Tracking your cycle over several months gives you a much better picture of your own pattern than comparing yourself to a 28-day template. Whether you use an app, a calendar, or basal temperature readings, the goal is to learn your personal normal so you can spot meaningful changes when they happen.