A full menstrual cycle averages 28 days but normally ranges from 21 to 35 days. That cycle breaks into four distinct phases, each driven by different hormones and lasting anywhere from less than a day to three weeks. Here’s how long each one typically runs and what affects the timing.
Menstrual Phase: 2 to 7 Days
The menstrual phase is the bleeding portion of your cycle, starting on day one. Most people bleed for 3 to 5 days, though anything from 2 to 7 days falls within the normal range. Flow is usually heaviest in the first two days, then gradually tapers off. During this time, your uterus is shedding the lining it built up during the previous cycle.
Bleeding that consistently lasts longer than 7 days is considered prolonged and worth investigating. Very heavy flow that soaks through a pad or tampon every hour for several consecutive hours is also outside the typical range.
Follicular Phase: 14 to 21 Days
The follicular phase overlaps with menstruation, starting on the same day your period begins and lasting until ovulation. According to Cleveland Clinic, it typically runs 14 to 21 days. This is the most variable phase of the entire cycle, and it’s the main reason cycle lengths differ so much from person to person and month to month.
During this phase, your brain signals your ovaries to start developing small fluid-filled sacs called follicles. One follicle eventually becomes dominant and produces a mature egg. How quickly that dominant follicle matures determines how long the phase lasts. If it takes longer, your whole cycle stretches out. If it’s faster, your cycle shortens. Rising estrogen levels thicken the uterine lining in preparation for a possible pregnancy.
This variability is why tracking ovulation matters more than counting calendar days if you’re trying to conceive or avoid pregnancy. A “late” period often just means the follicular phase ran a few days longer than usual, not that something is wrong.
Ovulatory Phase: 12 to 24 Hours
Ovulation itself is the shortest phase, lasting roughly 12 to 24 hours. It’s the window during which a mature egg is released from the ovary and is available for fertilization. The trigger is a sharp spike in luteinizing hormone (LH). This LH surge begins about 36 hours before ovulation, peaks, and then the egg is released 8 to 20 hours after that peak.
While the egg only survives about a day, the fertile window around ovulation is wider because sperm can live in the reproductive tract for up to five days. So the practical window for conception stretches to roughly six days, even though ovulation itself is brief.
Luteal Phase: 12 to 14 Days
After ovulation, the luteal phase begins and lasts until your next period starts. Unlike the follicular phase, the luteal phase is remarkably consistent. It typically runs 12 to 14 days, though it can range from 11 to 17 days. Once you know your personal luteal phase length, it tends to stay fairly stable cycle to cycle.
During this phase, the empty follicle transforms into a structure that produces progesterone. Progesterone maintains the uterine lining so a fertilized egg could implant. If no implantation occurs, progesterone drops, the lining breaks down, and your period starts.
A luteal phase of 10 days or fewer is considered a luteal phase deficiency by the American Society for Reproductive Medicine. A consistently short luteal phase can make it harder for a fertilized egg to implant successfully, which is one reason it’s relevant for anyone tracking fertility.
How These Phases Change With Age
Cycle length and phase timing shift across your lifetime, and the pattern isn’t a straight line. A large study from the Harvard T.H. Chan School of Public Health tracked how cycles vary by age and found some clear trends.
Teenagers and young adults under 20 had the longest average cycles at 30.3 days, with the most cycle-to-cycle variation at about 5.3 days. By ages 35 to 39, cycles settled into their most predictable pattern, averaging 28.7 days with only 3.8 days of variation. People in their early to mid-40s had slightly shorter cycles (averaging 28.2 days) as ovarian function began declining and the follicular phase shortened. After 50, cycles lengthened again and became much less predictable, varying by an average of 11.2 days as perimenopause progressed.
Most of this age-related change happens in the follicular phase, since the luteal phase stays relatively fixed throughout reproductive life.
What Makes Your Phases Shorter or Longer
Stress is one of the most common disruptors. When your body perceives sustained stress, cortisol rises and can suppress the hormonal signals that trigger follicle development and ovulation. In practical terms, this means the follicular phase can drag on longer than usual, delaying ovulation and pushing your period back. In more extreme cases, chronic high cortisol can block ovulation entirely, leading to a missed period or a cycle where bleeding happens but no egg was actually released.
Significant changes in body weight, intense exercise, illness, travel, and disrupted sleep can all have similar effects, primarily by lengthening or disrupting the follicular phase. Because the luteal phase is hormonally more rigid, external stressors are less likely to change its length. So if your cycle suddenly runs long, the follicular phase is almost always the culprit.
Hormonal birth control overrides these natural phase lengths entirely by supplying synthetic hormones that prevent ovulation, so the “phases” on birth control don’t follow the same timeline. If you’ve recently stopped hormonal contraception, it can take several months for your natural phase lengths to re-establish.