Menstrual Cycle Phases Explained

• Researched and written by: Dr Akshara CH, MBBS
• Medical inputs by: Dr Poonguzhali Liston, MBBS, MS OBG, FMAS, DRM, FRM, CIMP
• Medically reviewed by: Dr Yash Bahuguna, MBBS, MS, DNB, ISGE Certified Practitioner for PCOS

TL;DR

• The menstrual cycle is a natural, hormone-regulated process that begins on the first day of menstrual bleeding and ends the day before the next period starts.
  

• It unfolds across five phases, each shaped by shifts in hormones released by the brain and ovaries.
  

• These hormonal changes influence the whole body, affecting energy levels, mood, digestion, sleep, appetite, and physical comfort, not just the reproductive system.
  

• Cycle length, ovulation timing, and symptoms vary between individuals and can also change from one cycle to the next.
  

• Understanding the phases of the menstrual cycle helps place common symptoms in context, recognise personal patterns over time, and notice changes that persist, worsen may be useful signals to seek medical attention.[1,2]

What Is the Menstrual Cycle?

The menstrual cycle is a repeating pattern of hormonal and physical changes that prepares your body for a possible pregnancy each month. A cycle starts on the first day of menstrual bleeding and ends the day before the next period begins.[1] Many people hear that a cycle is “28 days,” but that is just an average. A normal cycle can range from 21 to 35 days in adults and from 21 to 45 days in adolescents. Small month-to-month variations are normal.[1,6]

This monthly rhythm is controlled by hormones that are chemical messengers in the body released by the brain, the pituitary gland which is a hormone-releasing gland at the base of the brain, and the ovaries. Together, these hormones coordinate ovulation, your period and changes in the uterine lining that prepare the body for pregnancy.[2] If pregnancy does not occur, hormone levels fall and the cycle starts again.

The Phases of the Menstrual Cycle

The menstrual cycle is often divided into phases based on predictable hormone patterns and changes in the brain, ovaries, and uterus. Many explanations describe four phases, but separating out a premenstrual phase helps explain why symptoms often change toward the end of the cycle. Together, these phases make up one complete menstrual cycle, with changes in the ovaries (ovarian cycle) and the uterus (uterine cycle) happening at the same time.

Menstrual phase: Your period

This is the part of the cycle when your period occurs and the body resets after the previous cycle. The menstrual phase begins when pregnancy does not occur and levels of estrogen and progesterone fall. This drop signals the uterus to shed its lining, called the endometrium, which leaves the body as menstrual blood through the vagina.[1]

Bleeding usually lasts between about three and eight days, though this varies from person to person.[1] During this time, cramping is common. These cramps are largely caused by prostaglandins, hormone-like substances released from the uterine lining, which make the uterus contract so the lining can be shed. 

Higher prostaglandin levels can also irritate nearby nerves and tissues. This helps explain why period pain can spread beyond the uterus and be felt in the lower back, inner thighs, or legs. Prostaglandins can also affect the gut, which helps explain symptoms like nausea or loose stools during periods.[3]

Follicular phase: Egg development

As bleeding ends, hormone levels begin to rise and the body starts preparing for ovulation. The follicular phase starts on day one of the cycle and overlaps with menstruation, but it becomes more noticeable once bleeding ends. In an average cycle, it often lasts about a week after the period finishes, though the length can vary.[1]

During this time, the pituitary gland in the brain releases follicle stimulating hormone (FSH), which helps the ovaries prepare an egg for ovulation. FSH tells the ovaries to mature follicles which are small fluid-filled structures that each contain an egg.[2]

As one follicle continues to grow, it releases estrogen. Estrogen helps rebuild and thicken the uterine lining after a period, preparing it to support a pregnancy if fertilisation happens.[1]

Ovulatory phase: Fertile window

This is the brief window when an egg is released and conception is most likely. Ovulation usually happens around the middle of the cycle, but the exact timing can shift from month to month. In a 28-day cycle, ovulation often occurs around day 14. As one follicle becomes dominant and gets ready to release an egg, it produces more estrogen. Estrogen levels rise and peak just before ovulation. This high estrogen level signals the brain to release a sudden surge of luteinising hormone (LH), known as the LH surge, which triggers egg release (ovulation). After the LH surge, estrogen levels briefly fall, which may help explain why some people notice light mid cycle spotting around ovulation.[1]

Once released, the egg survives for about 12 to 24 hours. Sperm can survive inside the reproductive tract for several days, which is why the fertile window includes the days before ovulation as well as the day ovulation occurs.[4] Around this time, cervical mucus becomes clearer and more slippery, helping sperm move and survive more easily.[7]

Luteal phase: Post-ovulation

After ovulation, the body shifts towards the luteal phase, which usually lasts about 14 days. It is one of the more consistent phases of the cycle for many women.[1] After the egg is released, the ovary forms a temporary structure called the corpus luteum, which releases progesterone. This hormone supports the uterine lining and prepares the body in case pregnancy occurs.[2]

Progesterone also affects the rest of the body. It causes a small rise in resting body temperature, slows digestion, and increases overall energy needs.[1] These changes help explain why appetite, sleep needs, or feelings of heaviness may increase. If pregnancy does not occur, the corpus luteum breaks down, progesterone levels fall, and the body begins shifting toward the next period.[1]

Premenstrual phase: Before the next period

In the final days of the cycle, around a week before your period, hormone levels drop and symptoms may become more noticeable. The premenstrual phase refers to the last part of the luteal phase, just before menstruation starts. During this time, estrogen and progesterone levels fall more sharply. This hormone drop can influence serotonin, a brain chemical involved in mood, sleep, and emotional regulation.[5]

As serotonin levels shift, some women notice bloating, fatigue, irritability, low mood, cravings, or changes in sleep.[5] These symptoms are together termed as premenstrual syndrome (PMS). Everyone’s experiences vary widely. Some may notice a change in the intensity of their symptoms every cycle, while others may not have any symptoms. 

Berry’s Insight: Your Hormone Timeline and Why Every Cycle Can Feel Different

Across your menstrual cycle, estrogen and progesterone follow a predictable pattern. Estrogen gradually rises during the follicular phase, peaks around ovulation, and falls in the days leading up to your period. Progesterone follows a different rhythm, increasing after ovulation and dropping sharply before the next cycle begins.[1,2] 

While these hormonal shifts are consistent, how a cycle feels can vary from month to month. Symptoms are shaped not only by hormone levels, but also by factors such as:

• Lifestyle factors: Stress, poor sleep, illness, travel, changes in routine, and irregular meals.

• Hormonal sensitivity: Some people are more sensitive to normal hormone changes across the menstrual cycle, especially in the days leading up to a period. In conditions like premenstrual syndrome or premenstrual dysphoric disorder, this increased sensitivity, rather than abnormal hormone levels, can influence how changes are experienced, and it varies widely between individuals.[3]

• Underlying medical conditions: Thyroid disorders, or anemia may amplify symptoms or make them feel less predictable across cycles.

Tracking Your Cycle: What to Notice in Each Phase

Tracking your cycle is a way to understand how your mood, energy, and physical symptoms tend to shift across different phases, and to notice when something feels different.[1,2]

Menstrual phase

• What happens in your body: Estrogen and progesterone levels are low, and your uterine lining sheds as menstrual bleeding begins.[1,2]

• Mood: You may feel more inward focused or emotionally sensitive during bleeding. Some women notice low mood or reduced motivation at this time, while others feel emotionally neutral.[1,6]

• Energy: Energy levels are often lower, especially in the first few days of your period.[1,2]

• Physical symptoms: You may experience menstrual bleeding, lower abdominal cramps caused by uterine contractions, back pain or headaches that occur along with cramps, and digestive symptoms such as nausea or loose stools in some people.[3]

Follicular phase

• What happens in your body: Bleeding ends, estrogen begins to rise, and the uterine lining starts rebuilding. Eggs in the ovaries begin developing for the next ovulation.[1,2]

• Mood: As estrogen rises, you may notice clearer thinking or a gradual lift in mood. Emotional steadiness often improves during this phase, though this varies from person to person.[1,2]

• Energy: Energy and focus often begin to improve after your period ends.[1]

• Physical symptoms: Pain and heaviness usually ease, and vaginal discharge may feel lighter or drier early in this phase.[1]

Ovulation

• What happens in your body: An egg is released from the ovary as estrogen reaches its highest level.[1,2]

• Mood: Some women feel more socially comfortable or mentally alert around ovulation, though this is not universal and may be subtle.[2]

• Energy: You may notice a short window of more stable or higher energy around this time.

• Physical symptoms: Vaginal discharge may become clearer, wetter, or more slippery.[4,7] Some women feel a brief, mild ache on one side of the lower abdomen, known as ovulation pain or mittelschmerz.[1] (can link ovulation cramps article)

In cycles with a regular luteal phase, ovulation typically occurs about 12–16 days before the next period.[1,6]

Fertility awareness cues: Changes in cervical mucus can help identify the fertile window. A rise in basal body temperature refers to a small increase in your resting body temperature that happens after ovulation, confirming that ovulation has already occurred rather than predicting it.[7]

Luteal phase

• What happens in your body: After ovulation, progesterone rises to support the uterine lining.[2]

• Mood: Early in this phase, you may feel calmer or more emotionally settled. As progesterone remains high, some women notice increased emotional sensitivity, especially if they are prone to premenstrual symptoms.[5]

• Energy: Energy may feel steady at first and then gradually decline as the phase progresses.[1]

• Physical symptoms: Resting body temperature stays slightly higher than earlier in the cycle. Digestion may slow in some people, leading to a fuller or heavier feeling.[1,2]

Premenstrual phase

• What happens in your body: Estrogen and progesterone levels fall in the days before menstruation begins.[1,2]

• Mood: You may notice irritability, low mood, or emotional reactivity if you are sensitive to hormonal changes. These mood shifts are commonly reported in premenstrual syndrome and related conditions, but they are not experienced by everyone.[5,6]

• Energy: Fatigue, poor sleep, or reduced stamina are commonly reported during the premenstrual days.[5]

• Physical symptoms: Bloating, breast tenderness, fluid retention, headaches, or body aches may occur in some women.[1,5]

Tip: Ovulation pain and cycle-related symptoms are common and usually mild, short-lived, and variable from cycle to cycle. Not everyone experiences the same signs, and no single symptom is required to confirm where you are in your cycle. Patterns that are severe, persistent, or clearly different from what is usual for you are worth discussing with your healthcare provider.[1]

When to Reach Out to a Doctor

Your cycle is an important health signal. When changes are persistent or clearly different from what is usual for you, a medical review can help clarify whether anything needs attention.

You may consider speaking to a doctor if you notice:

• Cycles that consistently fall outside the typical 21–35 day range in adulthood or become persistently unpredictable after previously being regular. It can suggest irregular ovulation and may be linked to hormonal imbalance, thyroid-related conditions, polycystic ovary syndrome (PCOS), or ongoing stress.
  

• Absent periods for three or more months when you are not pregnant, especially if cycles were previously regular.
  

• Heavy bleeding that lasts much longer than usual or becomes progressively heavier over time, even if it still occurs monthly.
  

• Bleeding between periods or after sex, which is not considered part of a normal menstrual cycle pattern.
  

• Period pain that is severe, worsening, or interferes with daily activities, particularly if it is new or different from your usual experience. 

These patterns are especially worth checking if they persist across multiple cycles rather than settling on their own.[1,2]

Reaching out does not automatically mean something is wrong. In many cases, it helps rule out concerns and gives you a clearer understanding of how your body is responding to factors like stress, health changes, or hormonal shifts.

What you can expect at the visit

Your doctor will usually start by looking at your cycle pattern over time. This often includes asking about the first day of bleeding across recent months, whether your cycles have shortened or lengthened, and whether changes coincided with stress, illness, weight changes, or lifestyle shifts. Depending on the pattern, they may recommend observation, cycle tracking, follow-up visits, or targeted tests to better understand how your hormones and ovulation are functioning.

The Bottom Line

The menstrual cycle is a natural, hormone-driven process that influences many systems in the body, not just the reproductive organs. Across the cycle, changes in hormones shape energy levels, mood, digestion, sleep, and physical comfort. Each phase is associated with predictable physiological shifts, which means the body’s needs can change from one part of the cycle to another.

Understanding these phases helps place common symptoms in context rather than viewing them as random or abnormal, which may be a useful cue to seek medical input that can help clarify whether the changes are related to normal hormonal variation or to something that may need further evaluation, such as hormonal imbalance or an underlying condition.

FAQs on Menstrual Cycle

What is considered a normal menstrual cycle length?

A normal menstrual cycle length for adults typically ranges from 21 to 35 days. What matters most is whether your cycle is fairly consistent for you.

Can menstrual cycles change over time?

Yes. Menstrual cycles may change with age, stress, illness, travel, pregnancy, contraception use, or as you approach perimenopause.

Is it normal for symptoms to vary from cycle to cycle?

Yes. Even with a regular cycle length, symptoms can differ from one cycle to the next depending on hormonal sensitivity and lifestyle factors.

When does ovulation usually happen?

Ovulation often occurs around the middle of the cycle. In a 28-day cycle, this is commonly around day 14, but timing can vary.

When should I speak to a doctor about my cycle?

You may consider speaking to a doctor if symptoms interfere with daily life, cycles become very irregular, or bleeding patterns change unexpectedly.

References

1. Thiyagarajan DK, Basit H, Jeanmonod R. Physiology, menstrual cycle. StatPearls. 2025 Jan. Accessed December 17, 2025.

2. National Institute of Child Health and Human Development. Menstrual cycle: overview. Accessed December 17, 2025.

3. Dawood MY. Primary dysmenorrhea: advances in pathogenesis and management. Lancet. 2006 May 13;367(9524):1613–1622.

4. Wilcox AJ, Dunson DB, Weinberg CR, Trussell J, Baird DD. Likelihood of conception with a single act of intercourse: providing benchmark rates for assessment of post-coital contraceptives. Hum Reprod. 2001 Jul;16(7):1399–1405.

5. Rapkin AJ, Mikacich JA. Premenstrual syndrome and premenstrual dysphoric disorder in adolescents. J Clin Endocrinol Metab. 2013 Apr;98(4):1223–1232.

6. American College of Obstetricians and Gynecologists. Menstruation in girls and adolescents: using the menstrual cycle as a vital sign. Accessed December 17, 2025.

7. American College of Obstetricians and Gynecologists. Fertility awareness–based methods of family planning. Accessed December 17, 2025.