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Published by Floriva · Updated 2026-04-28 · How Floriva checks its guides

Menstrual Cycle Phases: What Happens in Each Phase

A clear breakdown of the four menstrual cycle phases, the hormones driving each one, symptoms to expect, and what's worth logging for your health record.

The menstrual cycle is not just your period. It moves through four distinct phases driven by shifting hormones, each producing its own set of symptoms and body changes. Tracking what happens in each phase builds a personal baseline that makes irregularities easier to spot and clinical conversations more productive.

This guide is for educational purposes only and is not a substitute for medical advice.

The Four Phases of the Menstrual Cycle

The menstrual cycle is a recurring sequence of hormonal events that prepares the body for potential pregnancy. Most descriptions focus on the period itself, but the period is just one phase. Understanding what happens across all four phases explains the full range of symptoms you might experience throughout the month.

Phase 1: Menstrual Phase (Days 1 to 5, approximately)

The cycle officially starts on the first day of menstruation. When the previous cycle's egg was not fertilized, the corpus luteum breaks down, progesterone and estrogen levels drop, and the uterine lining sheds.

What happens hormonally: Both estrogen and progesterone are at their lowest levels. FSH begins to rise toward the end of menstruation, initiating the next round of follicle development.

Common symptoms:

  • Cramping, ranging from mild to severe

  • Lower back ache

  • Fatigue, often heavier in the first two days

  • Bloating that gradually eases as bleeding progresses

  • Headaches in some people

What to track: Flow volume (light, moderate, heavy, very heavy), number of days, clotting, pain intensity and location, any symptoms that affect daily functioning.

Heavy bleeding that soaks through a pad or tampon in an hour or less, or bleeding lasting more than 7 days, is worth reporting to a healthcare provider.

Phase 2: Follicular Phase (Days 1 to 13, approximately)

The follicular phase overlaps with menstruation at the start and continues until ovulation. FSH stimulates several follicles in the ovaries to develop; one dominant follicle emerges and grows, producing increasing amounts of estrogen.

What happens hormonally: Estrogen rises steadily. The uterine lining thickens and regenerates. Cervical mucus begins to change from absent or thick to thinner and more abundant.

Common symptoms:

  • Gradually improving energy as estrogen rises

  • Clearer skin in many people (estrogen has an anti-inflammatory effect)

  • Improved mood or focus, though this varies considerably

  • Increasing vaginal discharge as ovulation approaches

What to track: Energy levels, mood, discharge (amount and consistency), skin changes.

Phase 3: Ovulation (Around Day 14, but varies widely)

Ovulation is not a phase so much as an event. The LH surge triggers the dominant follicle to release a mature egg. The egg is viable for fertilization for roughly 12 to 24 hours, though sperm can survive in the reproductive tract for several days.

Common symptoms:

  • Mittelschmerz: one-sided lower abdominal twinge or ache (not universal)

  • Peak in cervical mucus, clear and stretchy

  • Slight increase in libido in some people

  • Possible slight dip then rise in basal body temperature

What to track: Any mid-cycle discomfort, changes in discharge, BBT if you are charting it, LH test results if you use ovulation predictor kits.

Ovulation timing is not fixed at day 14. In cycles that run 28 days, it may be around that point. In longer or shorter cycles, or under stress, ovulation shifts accordingly.

Phase 4: Luteal Phase (Days 15 to 28, approximately)

After ovulation, the ruptured follicle becomes the corpus luteum, which produces progesterone. Progesterone maintains the uterine lining in case of fertilization. If no fertilization occurs, the corpus luteum degrades around day 10 to 14 post-ovulation, progesterone and estrogen both fall, and menstruation begins again.

What happens hormonally: Progesterone dominates. A secondary estrogen rise occurs in the mid-luteal phase, then both hormones decline toward the end.

Common symptoms:

  • Bloating and water retention

  • Breast tenderness or fullness

  • Fatigue, heavier than in the follicular phase

  • Appetite changes, often with increased cravings

  • Mood changes: irritability, anxiety, or low mood in the days before menstruation

  • Mild constipation or digestive changes

What to track: Mood (daily, on a consistent scale), energy, physical symptoms, sleep quality, any symptoms that affect daily function.

For people with premenstrual dysphoric disorder (PMDD), the luteal phase is the critical window. See the PMDD tracking guide for symptom-specific logging guidance.

Why Track Across All Four Phases

Tracking only period days misses most of the cycle's information. A symptom that appears 10 days before your period is telling you something different than a symptom that starts with bleeding. Phase-aware tracking lets you:

  • Identify whether symptoms are cycle-related (by noting which phase they occur in)

  • Spot changes in cycle length or phase duration that might indicate hormonal shifts

  • Build a record that documents your personal baseline over time

What Changes Are Worth Noting to a Provider

Not every cycle variation requires attention. These patterns are worth discussing:

  • Cycles consistently shorter than 21 days or longer than 35 days

  • Luteal phases shorter than 10 days

  • Bleeding that is much heavier or lighter than your normal

  • New or worsening pain at any phase of the cycle

  • Significant changes in cycle length or regularity without an obvious cause

A Note on Tracking Privacy

Menstrual cycle data reveals a great deal about your health, fertility, reproductive history, and daily patterns. The detailed logs that make tracking medically useful are the same logs that make this data sensitive.

Period tracker apps that upload data to cloud servers expose this information to potential breaches, subpoenas, and third-party data-sharing arrangements. Flo Health, one of the most downloaded period apps, settled FTC action in 2021 for sharing user data with Facebook and Google. That settlement did not change the fundamental architecture of apps built on server-side data storage.

Apps that store data only on your device, with no cloud account required, have no data to share or subpoena. For detailed, long-term cycle tracking, the architecture of the app matters as much as its features.

Definitions

Follicular phase
The first half of the menstrual cycle, beginning on the first day of menstruation and ending at ovulation. During this phase, follicle-stimulating hormone (FSH) prompts several follicles in the ovaries to develop. Rising estrogen levels cause the uterine lining to thicken.
Ovulation
The release of a mature egg from a follicle in the ovary, triggered by a surge in luteinizing hormone (LH). Ovulation typically occurs around the midpoint of the cycle, though timing varies considerably between individuals and cycles.
Luteal phase
The second half of the cycle, from ovulation until menstruation begins. The ruptured follicle becomes the corpus luteum, which produces progesterone to maintain the uterine lining. If no fertilization occurs, the corpus luteum breaks down, progesterone drops, and menstruation begins.
Menstrual phase
The shedding of the uterine lining that occurs when progesterone and estrogen levels drop at the end of the luteal phase. It marks the first day of a new cycle and overlaps with the start of the next follicular phase.
Basal body temperature (BBT)
The body's resting temperature, measured first thing in the morning before any activity. BBT rises slightly after ovulation due to progesterone and remains elevated through the luteal phase. Tracking BBT over multiple cycles can help confirm ovulation timing.

Quick answers to the obvious questions.

How long is a normal menstrual cycle?

A typical cycle ranges from 21 to 35 days, with the average around 28 days. Cycle length is counted from the first day of one period to the first day of the next. Consistent cycles outside this range, or cycles that vary by more than a week from month to month, are worth discussing with a healthcare provider.

What cycle phase causes PMS symptoms?

PMS symptoms occur in the luteal phase, the days between ovulation and the start of menstruation. As progesterone rises and then falls late in the luteal phase, many people experience bloating, breast tenderness, mood changes, fatigue, and food cravings. Symptoms typically resolve within a day or two of the period starting.

Can I feel ovulation?

Some people notice ovulation physically. The most common sign is mittelschmerz, a one-sided lower abdominal ache or twinge that occurs around the time of egg release. Cervical mucus also changes around ovulation, becoming more abundant, clear, and stretchy, often described as similar to raw egg white. Not everyone feels ovulation distinctly.

Why does energy vary across the cycle?

Hormonal shifts affect energy, mood, and cognition throughout the cycle. Rising estrogen in the follicular phase tends to support higher energy and sharper focus. Progesterone in the luteal phase often has a more calming or fatiguing effect. These patterns vary by individual; tracking energy alongside cycle phase over several months reveals your personal pattern.

Questions people ask before they switch.

Is it normal for my cycle length to change from month to month?

Some variation is normal. Factors like stress, illness, travel, sleep disruption, significant weight change, or intense exercise can shift the timing of ovulation and alter cycle length. A variation of a few days is typical. Consistent large swings or very irregular cycles may warrant evaluation by a healthcare provider.

What is the difference between cycle length and period length?

Cycle length is the total time from the first day of one period to the first day of the next. Period length is just the duration of active bleeding, typically 2 to 7 days. The two are related but different measures. A long cycle does not mean a long period, and a short cycle does not mean a short period.

Should I be tracking my cycle if I am on hormonal birth control?

Hormonal contraceptives suppress or alter the natural cycle, so the phases described here may not apply in the same way. The bleeding on hormonal birth control is typically withdrawal bleeding rather than a true menstrual period. You can still track symptoms, mood, and physical changes, but the phase-by-phase hormone pattern will differ from a natural cycle.

Is my cycle data private if I use a period tracker app?

Not automatically. Many popular period tracker apps have server-based architectures, meaning your cycle dates, symptoms, and health data are uploaded and stored on company servers. Flo Health settled FTC action in 2021 for sharing user data with Facebook and Google. Period tracker data is not covered by HIPAA, so the legal protections are limited. Apps that store data only on your device, with no account required and no cloud sync, keep this information off servers entirely.