Periods & cycle

The Menstrual Cycle: Your Four Phases, Explained

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The menstrual cycle runs in four phases: menstruation, the follicular phase, ovulation, and the luteal phase. Estrogen and progesterone rise and fall across an average 24 to 38 days, shaping energy, mood, and discharge. The follicular phase varies most, while the luteal phase after ovulation stays close to two weeks.

Last updated: July 2026

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What are the four phases of the menstrual cycle?

The four phases are menstruation, the follicular phase, ovulation, and the luteal phase, and they repeat with each cycle. According to the American College of Obstetricians and Gynecologists, cycle length works as a vital sign, with a typical interval of about 24 to 38 days 1. Estrogen leads the first half, a luteinizing hormone surge triggers ovulation near the middle, and progesterone leads the second half 2.

Cycles are not identical month to month. Variation of up to 7 to 9 days between one cycle and the next is still considered regular in most adults 2. When yours rarely settles into any pattern, irregular periods have several common causes worth ruling out.

What happens during your period and the follicular phase?

Menstruation opens the cycle as the uterine lining sheds, usually lasting 2 to 7 days 1. Flow tends to be heaviest on the first day or two, then eases off. Because iron leaves the body in menstrual blood, long or heavy cycles can slowly lower iron stores, which is one reason some people feel tired from low iron 3.

The follicular phase overlaps with bleeding and continues after it. Estrogen climbs steadily, the lining rebuilds, and a single ovarian follicle becomes dominant. This stretch is the most variable part of the cycle, so a longer or shorter month usually reflects a longer or shorter follicular phase 2.

How does ovulation work and when does it happen?

Ovulation is the release of a mature egg, set off by a mid-cycle surge in luteinizing hormone. In a 28-day cycle it often falls near day 14, though timing shifts with cycle length because the follicular phase varies 2. The fertile window spans roughly 6 days — the five days before ovulation plus the day itself — because sperm can survive several days, according to reproductive medicine guidance 4.

Body signs can help you estimate timing. Cervical fluid turns clear and stretchy, and basal body temperature rises slightly afterward. When you want a closer read, here is how to tell when you are ovulating.

Why does the luteal phase affect how you feel?

The luteal phase follows ovulation and lasts a fairly steady 12 to 14 days 2. Progesterone rises to ready the uterine lining, then drops sharply if no pregnancy takes hold, which brings on the next period. That hormonal fall explains many premenstrual symptoms — bloating, breast tenderness, mood swings, and for some people migraines before a period.

Symptoms that are severe or disabling are worth flagging. Premenstrual syndrome is common, and a smaller share of people meet criteria for premenstrual dysphoric disorder, according to the Office on Women's Health 5. Tracking two or three cycles makes patterns easier to see and to share.

When cycle changes need a gynecologist

A clinician helps when your cycle shifts in ways that worry you or disrupt daily life. Periods that stop for several months, arrive fewer than 21 or more than 38 days apart, or soak through protection quickly are worth a conversation, according to gynecology guidelines 1. Bleeding between periods or any bleeding after menopause also deserves evaluation 5.

A primary care clinician or gynecologist can review your hormones, thyroid, and iron, and explain what is typical for your stage of life. Gale can help you prepare for that conversation.

Common questions

Most cycles run about 24 to 38 days, measured from the first day of one period to the first day of the next. Some month-to-month variation is normal. Cycles that are consistently shorter or longer, or that jump around a lot, are reasonable to mention to a clinician.

Your period marks the menstrual phase, day one being the first day of full flow. The follicular phase runs from then until ovulation, roughly mid-cycle. After the egg releases you enter the luteal phase, which lasts about two weeks until your next period begins.

Yes. The follicular phase is the most variable, so stress, illness, travel, and hormonal shifts can move ovulation earlier or later and change your total cycle length. The luteal phase after ovulation tends to stay more consistent, close to 12 to 14 days.

Not always. Day 14 is only an average for a textbook 28-day cycle. If your cycles are longer or shorter, ovulation shifts accordingly. Tracking cervical fluid, basal body temperature, or ovulation tests gives a more personal estimate than the calendar alone.

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When cycle changes are worth a check

  • —Periods that stop for three or more months without a known pregnancy — arrange a clinician visit
  • —Cycles consistently shorter than 21 days or longer than 38 days — raise it at your next appointment
  • —Bleeding between periods or after sex — have it evaluated
  • —Any vaginal bleeding after menopause — contact a clinician promptly

This article is general health education, not medical advice. What is typical for your cycle depends on your age, health history, and stage of life, which a primary care clinician or gynecologist can review with you.

References

  1. 1.American College of Obstetricians and Gynecologists (2015). ACOG Committee Opinion No. 651: Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign. Obstetrics & Gynecology. doi:10.1097/AOG.0000000000001215 ✓Establishes the menstrual cycle as a clinical vital sign and gives normal ranges for cycle interval (about 24 to 38 days) and menstrual duration (2 to 7 days).
  2. 2.Harlow SD, Gass M, Hall JE, et al. / STRAW+10 Collaborative Group (2012). Executive summary of the Stages of Reproductive Aging Workshop +10: addressing the unfinished agenda of staging reproductive aging. Menopause. doi:10.1097/gme.0b013e31824d8f40 ✓Defines normal cycle-length variation and the hormonal staging of the follicular and luteal phases across reproductive life.
  3. 3.MedlinePlus (National Library of Medicine) (2025). Ferritin Blood Test. MedlinePlus, U.S. National Library of Medicine (NIH). link ✓Explains that ferritin reflects the body's iron stores, supporting the link between menstrual blood loss and lowered iron.
  4. 4.Practice Committee of the American Society for Reproductive Medicine / SREI (2022). Optimizing natural fertility: a committee opinion. Fertility and Sterility. doi:10.1016/j.fertnstert.2021.10.007 ✓Describes ovulation timing and the roughly six-day fertile window, including sperm survival, from reproductive-medicine guidance.
  5. 5.Office on Women's Health (U.S. HHS) (2025). Period problems. Office on Women's Health (womenshealth.gov), U.S. HHS. link ✓Patient-facing overview of normal periods, PMS and PMDD, and when menstrual changes warrant evaluation.

5 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — every citation independently verified. Editorial policy

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